tomcat(11)org.apache.catalina.core.StandardWrapper源码剖析
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tomcat(11)org.apache.catalina.core.StandardWrapper源码剖析
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【0】README
0.0）本文部分文字描述轉(zhuǎn)自 “how tomcat works”，旨在學(xué)習(xí)?“tomcat(11)StandardWrapper源碼剖析” 的基礎(chǔ)知識；
0.1）StandardWrapper 是 Catalina中對Wrapper接口的標(biāo)準(zhǔn)實(shí)現(xiàn)；要知道，tomcat 中有4種類型的容器：Engine，Host，Context 和 Wrapper；（干貨——review ?tomcat 中有4種類型的容器：Engine，Host，Context 和 Wrapper）
【1】方法調(diào)用序列 1）對于每個(gè)引入的http 請求，連接器都會調(diào)用與其關(guān)聯(lián)的servlet容器的 invoke() 方法。然后，servlet容器會調(diào)用其所有子容器的invoke() 方法； 2）下圖展示了連接器接收到http 請求后的方法調(diào)用的協(xié)作圖；
3）上圖的具體steps 如下： step1）連接器創(chuàng)建 request 和 response對象； step2）連接器調(diào)用StandardContext.invoke()方法； step3）StandardContext.invoke()方法調(diào)用其管道的invoke() 方法。StandardContext的管道對象的基礎(chǔ)閥是 StandardCoantextValve類的實(shí)例，因此， StandardContext 的管道會調(diào)用 StandardContextValve.invoke()方法； step4）StandardContextValve.invoke()方法 獲取相應(yīng)的Wrapper 實(shí)例處理 http請求，調(diào)用Wrapper實(shí)例的invoke()方法； step5）StandardWrapper類是Wrapper接口的標(biāo)準(zhǔn)實(shí)現(xiàn)，StandardWrapper.invoke()方法 會調(diào)用其管道對象的invoke()方法； step6）StandardWrapper的管道對象中的基礎(chǔ)閥是 StandardWrapperValve 類的實(shí)例，因此，會調(diào)用StandardWrapperValve.invoke()方法，StandardWrapperValve.invoke()方法會調(diào)用Wrapper實(shí)例的 allocate() 方法獲取servlet實(shí)例； step7）allocate()方法調(diào)用load() 方法載入相應(yīng)的servlet類，若已經(jīng)載入，則無需重復(fù)載入； step8）load()方法調(diào)用servlet實(shí)例的init()方法； step9）StandardWrapperValve調(diào)用servlet.service()方法； // Call the filter chain for this request// NOTE: This also calls the servlet's service() methodtry { // org.apache.catalina.core.StandardWrapperValve.invoke()String jspFile = wrapper.getJspFile();if (jspFile != null)sreq.setAttribute(Globals.JSP_FILE_ATTR, jspFile);elsesreq.removeAttribute(Globals.JSP_FILE_ATTR);if ((servlet != null) && (filterChain != null)) {filterChain.doFilter(sreq, sres); // highlight line. doFilter() calls servlet.service()}sreq.removeAttribute(Globals.JSP_FILE_ATTR);} Attention）StandardContext類的構(gòu)造函數(shù)會設(shè)置StandardContextValve類的一個(gè)實(shí)例作為其基礎(chǔ)閥；? public StandardContext() { // org.apache.catalina.core.StardardContextsuper();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this); } Attention）StandardWrapper類的構(gòu)造函數(shù)也會設(shè)置一個(gè) StandardWrapperValve實(shí)例作為其基礎(chǔ)閥： public StandardWrapper() { // org.apache.catalina.core.StardardWrappersuper();swValve=new StandardWrapperValve();pipeline.setBasic(swValve); } 4）依據(jù)上述（3）小節(jié)中的 “處理http 請求的方法調(diào)用協(xié)作圖”，本文按照慣例給出了具體的調(diào)用過程，如下：
4.1）本文第一張是借用了 “tomcat(10)安全性中章節(jié)【6.4】中Supplement-補(bǔ)充模塊”的第2張圖；（for spec info，please visit tomcat(10)安全性），這旨在說明從HttpConnector -> StandardContext.invoke() -> StandardPipeline.invoke()的調(diào)用過程；
4.2）本文接著上面的調(diào)用過程繼續(xù)分析，調(diào)用過程如下圖；旨在說明? StandardPipeline.invoke() -> StandardContextValve.invoke() -> StandardWrapper.invoke() -> StandardPipeline.invoke() -> StandardWrapperValve.invoke() -> ApplicationFilterChain().doFilter()? ->?ApplicationFilterChain().internalDoFilter() -> HttpServlet(ModernServlet).service() -> ModernServlet->doGet() 的調(diào)用過程.（Bingo）
對上述協(xié)作圖和詳細(xì)調(diào)用過程圖的分析（Analysis）： A0）要知道Tomcat中有4種容器：Engine，Host，Context 和 Wrapper；（干貨——本文一直強(qiáng)調(diào)這一點(diǎn)，理解容器的層次結(jié)構(gòu)對于理解tomcat非常重要） A1）StandardContext 和 StandardWrapper 都是容器：他們都繼承自 ContainerBase，只不過StandardWrapper是StandardContext的子容器，而StandardWrapper是最小的容器，即它沒有子容器； A2）下面分別看StandardWrapper，StandardContext的構(gòu)造函數(shù)?和 ContainerBase 的變量定義； public final class StandardWrapper extends ContainerBase implements ServletConfig, Wrapper {public StandardWrapper() {super();swValve=new StandardWrapperValve();pipeline.setBasic(swValve);} } public class StandardContext extends ContainerBase implements Context {public StandardContext() { super();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this);} } public abstract class ContainerBase implements Container, Lifecycle, Pipeline {protected Pipeline pipeline = new StandardPipeline(this); // highlight line.protected HashMap children = new HashMap();protected int debug = 0; protected LifecycleSupport lifecycle = new LifecycleSupport(this); protected ArrayList listeners = new ArrayList(); protected Loader loader = null; protected Logger logger = null; protected Manager manager = null; protected Cluster cluster = null; protected Mapper mapper = null; protected HashMap mappers = new HashMap(); protected String mapperClass = null; protected String name = null; protected Container parent = null; protected ClassLoader parentClassLoader = null; protected Pipeline pipeline = new StandardPipeline(this); protected Realm realm = null; protected DirContext resources = null; protected static StringManager sm = StringManager.getManager(Constants.Package); protected boolean started = false; protected PropertyChangeSupport support = new PropertyChangeSupport(this); } A3）可以看到 父容器ContainerBase定義了管道StandardPipeline，而子容器StandardContext 設(shè)置StandardContextValve為基礎(chǔ)閥；而最小的容器StandardWrapper設(shè)置StandardWrapperValve為基礎(chǔ)閥； A4）也即 StandardContext 和?StandardWrapper 共用同一個(gè)管道，分別設(shè)置不同的基礎(chǔ)閥；（當(dāng)然，可以分別設(shè)置非基礎(chǔ)閥，非基礎(chǔ)閥在基礎(chǔ)閥被調(diào)用之前調(diào)用）；
【2】SingleThreadModel（已經(jīng)被棄用了） 1）intro：servlet類可以實(shí)現(xiàn) javax.servlet.SingleThreadModel 接口，這樣的servlet類也稱為 SingleThreadModel（STM）servlet類。根據(jù)servlet規(guī)范，實(shí)現(xiàn)此接口的目的是保證 servlet實(shí)例一次只處理一個(gè)請求； Attention）若 servlet類實(shí)現(xiàn) SingleThreadModel接口，則可以保證絕不會有兩個(gè)線程同時(shí)執(zhí)行該servlet.service()方法。這一點(diǎn)由 servlet容器通過控制對單一 servlet實(shí)例的同步訪問實(shí)現(xiàn)，或者維護(hù)一個(gè) servlet實(shí)例池，然后將每個(gè)新請求分派給一個(gè)空閑的servlet實(shí)例。該接口并不能防止servlet訪問共享資源造成的同步問題，例如訪問類的靜態(tài)變量或訪問servlet作用域之外的類； （干貨——有很多程序員哥哥沒有讀懂這段話，想當(dāng)然的認(rèn)為，實(shí)現(xiàn)了該接口的servlet就是線程安全的。這種想法是錯誤的，請?jiān)俣纫槐樯厦娴囊膬?nèi)容（原文作者說的，哈哈））
2）事實(shí)上，實(shí)現(xiàn)了 SingleThreadModel 接口的servlet類只能保證在同一時(shí)刻，只有一個(gè)線程在執(zhí)行該 servlet實(shí)例的service()方法。但，為了提高執(zhí)行 性能，servlet容器會創(chuàng)建多個(gè)STM servlet實(shí)例。也就是說，STM servlet.service()方法 會在多個(gè)STM?servlet實(shí)例中并發(fā)執(zhí)行。如果servlet實(shí)例需要靜態(tài)類變量或類外的某些資源的話，就有可能引起同步問題； Atttention）在servlet 2.4中，SingleThreadModel接口已經(jīng)被棄用了，因?yàn)樗鼤?servlet程序員誤以為該接口的servlet類就是多線程安全的；
【3】StandardWrapper 1）intro to?StandardWrapper：其主要任務(wù)是 載入它所代表的servlet類，并進(jìn)行實(shí)例化； 2）StandardWrapper并不調(diào)用servlet的service方法，該任務(wù)由 StandardWrapperValve對象（StandardWrapper實(shí)例的管道對象中的基礎(chǔ)閥）完成； 3）StandardWrapperValve對象通過調(diào)用allocate()方法從 StandardWrapper實(shí)例中獲取servlet實(shí)例，在獲得servlet實(shí)例后，StandardWrapperValve實(shí)例就會調(diào)用servlet實(shí)例的service()方法； 【3.1】分配servlet實(shí)例? 1）分配servlet實(shí)例是由 StandardWrapper.allocate()方法來完成的（allocate方法返回請求的servelt實(shí)例）； 2）allocate()方法分為兩部分（parts）： p1）第一部分：?allocate()首先檢查 instance是否為null，若是， 則allocate()方法調(diào)用 loadServlet()方法載入相關(guān)的servlet類，然后 整型變量countAllocated加1，返回instance的值； p2）第二部分： p2.1）若StandardWrapper表示的servlet是一個(gè)STM servlet類，則allocate()會試圖從對象池中返回一個(gè)servlet實(shí)例。變量 instancePool 是一個(gè) java.util.Stack類型的棧，其中保存了所有的STM servlet實(shí)例： private Stack instancePool = null; p2.2）只要STM servlet實(shí)例數(shù)不超過指定的最大值，allocate()方法會返回一個(gè) STM servlet實(shí)例。整型變量maxInstances 保存了在棧中存儲的 STM servlet實(shí)例的最大值，default value = 20； private int maxInstances = 20; p2.3）而 nInstances 保存了當(dāng)前 STM servlet實(shí)例的數(shù)量（初始為0）；
step1）檢查當(dāng)前的StandardWrapper類是否表示的是一個(gè) STM servlet類，若不是，且變量instance不為null（表示以前已經(jīng)載入過這個(gè)servlet），它就直接返回該實(shí)例； // Nothing to do if we already have an instance or an instance poolif (!singleThreadModel && (instance != null))return instance; step2）獲得 System.out 和 System.err 的輸出，便于它使用 javax.servlet.ServletConfig.log() 方法記錄日志消息： PrintStream out = System.out;if (swallowOutput) {SystemLogHandler.startCapture();} step3）定義類型為javax.servlet.Servlet 名為servlet 的變量，其表示已載入的servlet實(shí)例，會由 loadServlet()方法返回； Servlet servlet = null; step4）由于Catalina是一個(gè)JSP容器，故loadServlet()方法必須檢查請求的servlet是不是一個(gè)jsp 頁面。若是，則loadServlet() 方法需要獲取代表該jsp 頁面的實(shí)際servlet類； String actualClass = servletClass;if ((actualClass == null) && (jspFile != null)) {Wrapper jspWrapper = (Wrapper)((Context) getParent()).findChild(Constants.JSP_SERVLET_NAME);if (jspWrapper != null)actualClass = jspWrapper.getServletClass(); } // public static final String JSP_SERVLET_NAME = "jsp";<span style="font-family: SimSun; line-height: 1.5; background-color: inherit;">? ? ? ? ? ?</span> step5）如果找不到該jsp 頁面的servlet類，則會使用變量 servletClass（actualClass）的值。若沒有調(diào)用StandardWrapper.serServletClass() 方法設(shè)置servletClass的值，則會拋出異常，并停止執(zhí)行后續(xù)方法； // Complain if no servlet class has been specifiedif (actualClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.notClass", getName()));}<span style="font-family: SimSun; background-color: rgb(255, 255, 255);">? ? ? ? ? ?</span> step6）這時(shí)，要載入的servlet類名已經(jīng)解析完了，loadServlet()方法會獲取載入器 Loader loader = getLoader();public Loader getLoader() { // org.apache.catalina.core.ContainerBase.getLoader();if (loader != null)return (loader);if (parent != null)return (parent.getLoader());return (null);} step7）若找到載入器（loader），則loadServlet()方法調(diào)用getClassLoader()方法獲取一個(gè)ClassLoader； ClassLoader classLoader = loader.getClassLoader(); step8）Catalina提供了一些用于訪問servlet容器內(nèi)部數(shù)據(jù)的專用servlet類。如果某個(gè)servlet類是這種專用的servlet，即若isContainerProvidedServlet()方法返回true，則變量 classLoader被賦值為另一種ClassLoader實(shí)例，如此一來，這個(gè)servlet實(shí)例就可以訪問Catalina的內(nèi)部數(shù)據(jù)了； // Special case class loader for a container provided servletif (isContainerProvidedServlet(actualClass)) {classLoader = this.getClass().getClassLoader();log(sm.getString("standardWrapper.containerServlet", getName()));} step9）準(zhǔn)備好類載入器和準(zhǔn)備載入的servlet類名后，loadServlet()方法就可以載入servlet類了； // Load the specified servlet class from the appropriate class loaderClass classClass = null;try {if (classLoader != null) {classClass = classLoader.loadClass(actualClass);} else {classClass = Class.forName(actualClass);}} catch (ClassNotFoundException e) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass),e);} if (classClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass));} step10）實(shí)例化該servlet ? ? ? // Instantiate and initialize an instance of the servlet class itselftry {servlet = (Servlet) classClass.newInstance();} catch (ClassCastException e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.notServlet", actualClass), e);} catch (Throwable e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.instantiate", actualClass), e);}
step11）在loadServlet()方法實(shí)例化這個(gè)servlet之前，它會調(diào)用 isServletAllowed()方法檢查該servlet 類是否允許載入：? ? ? // Check if loading the servlet in this web application should be// allowedif (!isServletAllowed(servlet)) {throw new SecurityException(sm.getString("standardWrapper.privilegedServlet",actualClass));}
step12）若通過了安全檢查，它還會繼續(xù)檢查該servlet類是否是一個(gè) ContainerServlet類型的servlet（實(shí)現(xiàn)了 org.apache.catalina.ContainerServlet接口的 servlet可以訪問Catalina的內(nèi)部功能）。若該servlet類是一個(gè) ContainerServlet，loadServlet()方法會調(diào)用 ContainerServlet.setWrapper()，傳入StandardWrapper實(shí)例；? // Special handling for ContainerServlet instancesif ((servlet instanceof ContainerServlet) &&isContainerProvidedServlet(actualClass)) {((ContainerServlet) servlet).setWrapper(this);} step13）觸發(fā)BEFORE_INIT_EVENT事件，調(diào)用servlet實(shí)例的 init()方法（init()方法傳入了javax.servlet.ServletConfig外觀對象）：? // Call the initialization method of this servlettry {instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_INIT_EVENT,servlet);servlet.init(facade); // highlight line. step14）若變量 loadOnStartup 大于0， 且被請求的servlet類實(shí)際上是一個(gè)jsp 頁面，則servlet實(shí)例的service()方法；? if ((loadOnStartup >= 0) && (jspFile != null)) {// Invoking jspInitHttpRequestBase req = new HttpRequestBase();HttpResponseBase res = new HttpResponseBase();req.setServletPath(jspFile);req.setQueryString("jsp_precompile=true");servlet.service(req, res); // highlight line.}instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet); step15）觸發(fā)AFTER_INIT_EVENT事件 instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT, step16）若StandardWrapper對象表示的servlet類是一個(gè)STM servlet，則將該servlet實(shí)例添加到servlet實(shí)例池中。因此會判斷 instancePool 是否為null，若是，則要給他賦值一個(gè)Stack 對象；? // Register our newly initialized instancesingleThreadModel = servlet instanceof SingleThreadModel;if (singleThreadModel) {if (instancePool == null)instancePool = new Stack(); // highlight line. } step17）在finally代碼塊中，loadServlet()方法停止捕獲System.out 和 System.err 對象，記錄在載入 ServletContext.log()方法的過程中產(chǎn)生的日志消息； finally {if (swallowOutput) {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {if (getServletContext() != null) {getServletContext().log(log); // highlight line.} else {out.println(log);}}}} public ServletContext getServletContext() { org.apache.catalina.core.StandardWrapper.getServletContext()if (parent == null)return (null);else if (!(parent instanceof Context))return (null);elsereturn (((Context) parent).getServletContext());} step18）最后返回已載入的servlet實(shí)例； return servlet; 【3.3】ServletConfig對象 1）intro：在上述step13）中提到了 servlet.init(facade)，而facade 是 javax.servlet.ServletConfig對象的一個(gè)外觀變量； 2）StandardWrapper對象是如何獲取 servletConfig 對象的？答案就在 StandardWrapper中，該類不僅實(shí)現(xiàn)了 Wrapper接口，還實(shí)現(xiàn)了 javax.servlet.ServletConfig 接口； public final class StandardWrapper extends ContainerBase implements ServletConfig, Wrapper { // org.apache.catalina.core.StandardWrapper // ...... } public interface ServletConfig { // javax.servlet.ServletConfig public String getServletName();public ServletContext getServletContext(); public String getInitParameter(String name);public Enumeration getInitParameterNames(); } 3）javax.servlet.ServletConfig 接口有4個(gè)方法：getServletContext() , getServletName(), ?getInitParameter()， ?getInitParameterNames()方法；下面對這4個(gè)方法進(jìn)行說明； method1）getServletConfig()方法： public ServletContext getServletContext() { // org.apache.catalina.core.StandardWrapper.getServletContext()if (parent == null)return (null);else if (!(parent instanceof Context))return (null);elsereturn (((Context) parent).getServletContext());}/*** Return the servlet context for which this Context is a facade.*/public ServletContext getServletContext() { // org.apache.catalina.core.StandardContext.getServletContext()if (context == null)context = new ApplicationContext(getBasePath(), this);return (context);} Attention）正如以上代碼所展示的那樣，無法單獨(dú)使用一個(gè)Wrapper實(shí)例來表示一個(gè) servlet 類的定義。Wrapper 實(shí)例必須駐留在某個(gè) Context 容器中，這樣，當(dāng)調(diào)用其父容器的getServletConfig()方法時(shí)，才能返回ServletContext類的一個(gè)實(shí)例； method2）getServletName()方法：該方法返回 servlet類的名字，該方法的簽名如下： ?public String getServletName() { // org.apache.catalina.core.StandardWrapper.getServletName()return (getName());} public String getName() { // org.apache.catalina.core.ContainerBase.getName(). // 因?yàn)?public final class StandardWrapper extends ContainerBasereturn (name);} method3）getInitParameter()方法：該方法返回指定初始參數(shù)的值 public String getInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.getInitParameter()return (findInitParameter(name));} public String findInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.findInitParameter()synchronized (parameters) {return ((String) parameters.get(name));}} 對getInitParameter（）方法的分析（Analysis）： A1）在StandardWrapper類中，初始化參數(shù) parameters 存儲在一個(gè) HashMap類型中； private HashMap parameters = new HashMap(); A2）通過addInitParameter()方法，傳入?yún)?shù)的名字 和 對應(yīng)的值 來填充變量 parameters 的值： public void addInitParameter(String name, String value) { // org.apache.catalina.core.StandardWrapper.addInitParameter().synchronized (parameters) {parameters.put(name, value);}fireContainerEvent("addInitParameter", name); // highlight line.} public void fireContainerEvent(String type, Object data) {// org.apache.catalina.core.ContainerBase.fireContainerEvent().if (listeners.size() < 1)return;ContainerEvent event = new ContainerEvent(this, type, data);ContainerListener list[] = new ContainerListener[0];synchronized (listeners) {list = (ContainerListener[]) listeners.toArray(list);}for (int i = 0; i < list.length; i++)((ContainerListener) list[i]).containerEvent(event);} A3）StandardWrapper.getInitParameter()方法的實(shí)現(xiàn)如下：? public String getInitParameter(String name) {return (findInitParameter(name));} A4）findInitParameter()方法接收一個(gè)指定的初始化參數(shù)名的字符串變量，調(diào)用HashMap 變量 parameters的get()方法獲取初始化參數(shù)的值； public String findInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.findInitParameter()synchronized (parameters) {return ((String) parameters.get(name)); // highlight line.}} method4）getInitParameterNames()方法： 該方法返回所有初始化參數(shù)的名字的集合，實(shí)際上是 java.util.Enumeration的實(shí)例；? public Enumeration getInitParameterNames() {synchronized (parameters) {return (new Enumerator(parameters.keySet()));}} 【3.4】servlet容器的父子關(guān)系 1）intro to StandardWrapper：Wrapper實(shí)例代表一個(gè)servlet實(shí)例，是最低級的容器，故Wrapper不能再有子容器，不應(yīng)該調(diào)用addChild()方法添加子容器，否則拋出 java.lang.IllegalStateException 異常；（干貨review——Wrapper實(shí)例代表一個(gè)servlet實(shí)例，是最低級的容器，故Wrapper不能再有子容器） 2）org.apache.catalina.core.StandardWrapper.addChild()方法實(shí)現(xiàn)如下： public void addChild(Container child) {throw new IllegalStateException (sm.getString("standardWrapper.notChild"));} Attention）Wrapper容器的父容器只能是 Context 容器；若我們在設(shè)置父容器的時(shí)候，傳入了非Context容器，則拋出 java.lang.IllegalArgumentException 異常； public void setParent(Container container) { // org.apache.catalina.core.StandardWrapper.setParent().if ((container != null) && !(container instanceof Context)) throw new IllegalArgumentException(sm.getString("standardWrapper.notContext"));if (container instanceof StandardContext) {swallowOutput = ((StandardContext)container).getSwallowOutput();}super.setParent(container); // highlight line.} public void setParent(Container container) { // org.apache.catalina.core.ContainerBase.setParent().Container oldParent = this.parent;this.parent = container;support.firePropertyChange("parent", oldParent, this.parent);}
【4】 StandardWrapperFacade類?（干貨——應(yīng)用了設(shè)計(jì)模式中的外觀模式） 1）problem+solution： 1.1）problem：StandardWrapper實(shí)例會調(diào)用它所載入的servlet類的實(shí)例的init()方法。init()方法需要一個(gè)javax.servlet.ServletConfig 實(shí)例，而StandardWrapper了本身也實(shí)現(xiàn)了 javax.servlet.ServletConfig 接口，所以，理論上 StandardWrapper需要將其中大部分公共方法對servlet程序員隱藏起來； 1.2）solution：為了實(shí)現(xiàn)這個(gè)目的，StandardWrapper類將自身實(shí)例包裝成 StandardWrapperFacade類的一個(gè)實(shí)例；
2）StandardWrapper類創(chuàng)建StandardWrapperFacade對象，并將自身作為參數(shù)傳入StandardWrapperFacade的構(gòu)造器； private StandardWrapperFacade facade = new StandardWrapperFacade(this); // defined in StandardWrapper.java 3）StandardWrapperFacade的構(gòu)造函數(shù)； public StandardWrapperFacade(StandardWrapper config) {super();this.config = (ServletConfig) config; // private ServletConfig config = null;} 4）因此當(dāng)創(chuàng)建StandardWrapper對象調(diào)用servlet實(shí)例的 init()方法時(shí)，它會傳入StandardWrapperFacade類的一個(gè)實(shí)例。這樣，在servlet實(shí)例內(nèi)調(diào)用 ServletConfig.getServletName(),ServletConfig.getInitParameter(), getInitParameterNames() ，getServletContext()方法會直接傳遞給 StandardWrapper類的相應(yīng)方法； 5）org.apache.catalina.core.StandardWrapperFacade 的定義如下： public final class StandardWrapperFacade implements ServletConfig {public StandardWrapperFacade(StandardWrapper config) {super();this.config = (ServletConfig) config;}public String getServletName() {return config.getServletName();}public ServletContext getServletContext() {ServletContext theContext = config.getServletContext();if ((theContext != null) &&(theContext instanceof ApplicationContext))theContext = ((ApplicationContext) theContext).getFacade();return (theContext);}public String getInitParameter(String name) {return config.getInitParameter(name);}public Enumeration getInitParameterNames() {return config.getInitParameterNames();} }
【5】StandardWrapperValve類 1）StandardWrapperValve類是 StandardWrapper實(shí)例中的基礎(chǔ)閥，要完成兩個(gè)操作（Operations）： public StandardWrapper() { // StandardWrapper的構(gòu)造函數(shù)；super();swValve=new StandardWrapperValve();pipeline.setBasic(swValve);} O1）執(zhí)行與該servlet實(shí)例關(guān)聯(lián)的全部過濾器；（干貨——這里引入了過濾器） O2）調(diào)用servlet實(shí)例的service()方法； 2）完成上述任務(wù)后，在 StandardWrapperValve.invoke()方法實(shí)現(xiàn)中會執(zhí)行以下操作（Operations）： O1）調(diào)用StandardWrapper.allocate()方法獲取該StandardWrapper實(shí)例所表示的 servlet實(shí)例； public void invoke(Request request, Response response,ValveContext valveContext)throws IOException, ServletException {long t1=System.currentTimeMillis();requestCount++;// Initialize local variables we may needboolean unavailable = false;Throwable throwable = null;StandardWrapper wrapper = (StandardWrapper) getContainer();ServletRequest sreq = request.getRequest();ServletResponse sres = response.getResponse();Servlet servlet = null;HttpServletRequest hreq = null;if (sreq instanceof HttpServletRequest)hreq = (HttpServletRequest) sreq;HttpServletResponse hres = null;if (sres instanceof HttpServletResponse)hres = (HttpServletResponse) sres;// Check for the application being marked unavailableif (!((Context) wrapper.getParent()).getAvailable()) {hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,sm.getString("standardContext.isUnavailable"));unavailable = true;}// Check for the servlet being marked unavailableif (!unavailable && wrapper.isUnavailable()) {log(sm.getString("standardWrapper.isUnavailable",wrapper.getName()));if (hres == null) {; // NOTE - Not much we can do generically} else {long available = wrapper.getAvailable();if ((available > 0L) && (available < Long.MAX_VALUE))hres.setDateHeader("Retry-After", available);hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,sm.getString("standardWrapper.isUnavailable",wrapper.getName()));}unavailable = true;}// Allocate a servlet instance to process this requesttry {if (!unavailable) {servlet = wrapper.allocate(); // highlight line.} // ...... O2）調(diào)用私有方法 createFilterChain()，創(chuàng)建過濾器鏈； // Create the filter chain for this request ApplicationFilterChain filterChain = createFilterChain(request, servlet); // for create FilterChain方法，本章節(jié)末尾； private ApplicationFilterChain createFilterChain(Request request, Servlet servlet) { if (servlet == null)return (null);ApplicationFilterChain filterChain = new ApplicationFilterChain(); filterChain.setServlet(servlet);StandardWrapper wrapper = (StandardWrapper) getContainer();filterChain.setSupport(wrapper.getInstanceSupport());// Acquire the filter mappings for this ContextStandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();// If there are no filter mappings, we are doneif ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// Acquire the information we will need to match filter mappingsString requestPath = null;if (request instanceof HttpRequest) {HttpServletRequest hreq =(HttpServletRequest) request.getRequest();String contextPath = hreq.getContextPath();if (contextPath == null)contextPath = "";String requestURI = ((HttpRequest) request).getDecodedRequestURI();if (requestURI.length() >= contextPath.length())requestPath = requestURI.substring(contextPath.length());}String servletName = wrapper.getName();int n = 0;// Add the relevant path-mapped filters to this filter chainfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersURL(filterMaps[i], requestPath))continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}// Add filters that match on servlet name secondfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersServlet(filterMaps[i], servletName))continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}return (filterChain);} O3）調(diào)用過濾器鏈的 doFilter()方法，其中包括調(diào)用servlet實(shí)例的service()方法； try {String jspFile = wrapper.getJspFile();if (jspFile != null)sreq.setAttribute(Globals.JSP_FILE_ATTR, jspFile);elsesreq.removeAttribute(Globals.JSP_FILE_ATTR);if ((servlet != null) && (filterChain != null)) {filterChain.doFilter(sreq, sres); // hightlight line.}sreq.removeAttribute(Globals.JSP_FILE_ATTR); // ......public void doFilter(ServletRequest request, ServletResponse response) //org.apache.catlina.core.ApplicationFilterChain.doFileter()throws IOException, ServletException {if( System.getSecurityManager() != null ) {final ServletRequest req = request;final ServletResponse res = response;try {java.security.AccessController.doPrivileged(new java.security.PrivilegedExceptionAction(){public Object run() throws ServletException, IOException {internalDoFilter(req,res); // highlight line. internalDoFilter() 參見文末.return null;}});} catch( PrivilegedActionException pe) {Exception e = pe.getException();if (e instanceof ServletException)throw (ServletException) e;else if (e instanceof IOException)throw (IOException) e;else if (e instanceof RuntimeException)throw (RuntimeException) e;elsethrow new ServletException(e.getMessage(), e);}} else {internalDoFilter(request,response);}} private void internalDoFilter(ServletRequest request, ServletResponse response)throws IOException, ServletException { //org.apache.catalina.core.ApplicationFilterChain.internalDoFilter().// Construct an iterator the first time this method is calledif (this.iterator == null)this.iterator = filters.iterator();// Call the next filter if there is oneif (this.iterator.hasNext()) {ApplicationFilterConfig filterConfig =(ApplicationFilterConfig) iterator.next();Filter filter = null;try {filter = filterConfig.getFilter();support.fireInstanceEvent(InstanceEvent.BEFORE_FILTER_EVENT,filter, request, response);filter.doFilter(request, response, this);support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,filter, request, response);} //......return;}// We fell off the end of the chain -- call the servlet instancetry {support.fireInstanceEvent(InstanceEvent.BEFORE_SERVICE_EVENT,servlet, request, response);if ((request instanceof HttpServletRequest) &&(response instanceof HttpServletResponse)) { servlet.service((HttpServletRequest) request, (HttpServletResponse) response); // 這不就是你夢寐以求的service()方法嗎？哈哈。} else {servlet.service(request, response); // and this highlight line.}support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,servlet, request, response);} //......} O4）釋放過濾器鏈； try {if (filterChain != null)filterChain.release(); // highlight line.} catch (Throwable e) {log(sm.getString("standardWrapper.releaseFilters",wrapper.getName()), e);if (throwable == null) {throwable = e;exception(request, response, e);}} void release() { //org.apache.catalina.core.ApplicationFilterChain.release()this.filters.clear();this.iterator = iterator;this.servlet = null;} O5）調(diào)用Wrapper實(shí)例的 deallocate()方法； // Deallocate the allocated servlet instancetry {if (servlet != null) {wrapper.deallocate(servlet); // highlight line.}} catch (Throwable e) {log(sm.getString("standardWrapper.deallocateException",wrapper.getName()), e);if (throwable == null) {throwable = e;exception(request, response, e);}}public void deallocate(Servlet servlet) throws ServletException { //org.apache.catalina.core.StandardWrapper.deallocate()// If not SingleThreadModel, no action is requiredif (!singleThreadModel) {countAllocated--;return;}synchronized (instancePool) {countAllocated--;instancePool.push(servlet);instancePool.notify();}} O6）若該servlet類再也不會被使用到，調(diào)用Wrapper實(shí)例的unload()方法； // If this servlet has been marked permanently unavailable,// unload it and release this instancetry {if ((servlet != null) &&(wrapper.getAvailable() == Long.MAX_VALUE)) {wrapper.unload(); // highlight line.}} // ......long t2=System.currentTimeMillis();long time=t2-t1;processingTime+=time;if( time > maxTime ) maxTime=time;} Attention）以上調(diào)用過程中，最重要的是對 createFilterChain()方法和過濾器鏈的 doFilter()方法的調(diào)用。createFilterChain()方法創(chuàng)建一個(gè) ApplicationFilterChain實(shí)例，并將所有需要應(yīng)用到該Wrapper實(shí)例所代表的servlet實(shí)例的過濾器添加到其中； private ApplicationFilterChain createFilterChain(Request request,Servlet servlet) {if (servlet == null)return (null);ApplicationFilterChain filterChain =new ApplicationFilterChain();filterChain.setServlet(servlet);StandardWrapper wrapper = (StandardWrapper) getContainer();filterChain.setSupport(wrapper.getInstanceSupport());StandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();if ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// Acquire the information we will need to match filter mappingsString requestPath = null;if (request instanceof HttpRequest) {HttpServletRequest hreq =(HttpServletRequest) request.getRequest();String contextPath = hreq.getContextPath();if (contextPath == null)contextPath = "";String requestURI = ((HttpRequest) request).getDecodedRequestURI();if (requestURI.length() >= contextPath.length())requestPath = requestURI.substring(contextPath.length());}String servletName = wrapper.getName();int n = 0; // Add the relevant path-mapped filters to this filter chainfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersURL(filterMaps[i], requestPath)) continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue; }filterChain.addFilter(filterConfig); n++;}// Add filters that match on servlet name secondfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersServlet(filterMaps[i], servletName)) continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}return (filterChain); } public synchronized void unload() throws ServletException {if (!singleThreadModel && (instance == null))return;unloading = true;if (countAllocated > 0) {int nRetries = 0;while (nRetries < 10) {if (nRetries == 0) {log("Waiting for " + countAllocated +" instance(s) to be deallocated");}try {Thread.sleep(50);} catch (InterruptedException e) {;}nRetries++;}}ClassLoader oldCtxClassLoader =Thread.currentThread().getContextClassLoader();ClassLoader classLoader = instance.getClass().getClassLoader();PrintStream out = System.out;if (swallowOutput) {SystemLogHandler.startCapture();}try {instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_DESTROY_EVENT, instance);Thread.currentThread().setContextClassLoader(classLoader);instance.destroy();instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_DESTROY_EVENT, instance);} catch (Throwable t) {instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_DESTROY_EVENT, instance, t);instance = null;instancePool = null;nInstances = 0;fireContainerEvent("unload", this);unloading = false;throw new ServletException(sm.getString("standardWrapper.destroyException", getName()),t);} finally {Thread.currentThread().setContextClassLoader(oldCtxClassLoader);if (swallowOutput) {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {if (getServletContext() != null) {getServletContext().log(log);} else {out.println(log);}}}}instance = null;if (singleThreadModel && (instancePool != null)) {try {Thread.currentThread().setContextClassLoader(classLoader);while (!instancePool.isEmpty()) {((Servlet) instancePool.pop()).destroy();}} catch (Throwable t) {instancePool = null;nInstances = 0;unloading = false;fireContainerEvent("unload", this);throw new ServletException(sm.getString("standardWrapper.destroyException",getName()), t);} finally {Thread.currentThread().setContextClassLoader(oldCtxClassLoader);}instancePool = null;nInstances = 0;}singleThreadModel = false;unloading = false;fireContainerEvent("unload", this); }
【6】 FilterDef類（org.apache.catalina.deploy.FilterDef） 1）intro：FilterDef 是一個(gè)過濾器的定義； 2）FilterDef類中的每個(gè)屬性表示在定義filter元素時(shí)聲明的子元素。其中Map 類型的變量parameters 存儲了初始化過濾器時(shí)所需要的所有參數(shù)。addInitParameter()方法用于向parameters 中添加新的 name/value 形式的參數(shù)名和對應(yīng)的值； 3）其定義源碼如下： public final class FilterDef { // org.apache.catalina.deploy.FilterDef private String description = null;public String getDescription() {return (this.description);}public void setDescription(String description) {this.description = description;} private String displayName = null;public String getDisplayName() {return (this.displayName);}public void setDisplayName(String displayName) {this.displayName = displayName;}private String filterClass = null;public String getFilterClass() {return (this.filterClass);}public void setFilterClass(String filterClass) {this.filterClass = filterClass;} private String filterName = null;public String getFilterName() {return (this.filterName);}public void setFilterName(String filterName) {this.filterName = filterName;} private String largeIcon = null;public String getLargeIcon() {return (this.largeIcon);}public void setLargeIcon(String largeIcon) {this.largeIcon = largeIcon;} private Map parameters = new HashMap();public Map getParameterMap() {return (this.parameters);}private String smallIcon = null;public String getSmallIcon() {return (this.smallIcon);}public void setSmallIcon(String smallIcon) {this.smallIcon = smallIcon;} public void addInitParameter(String name, String value) {parameters.put(name, value);}public String toString() {StringBuffer sb = new StringBuffer("FilterDef[");sb.append("filterName=");sb.append(this.filterName);sb.append(", filterClass=");sb.append(this.filterClass);sb.append("]");return (sb.toString());} }
【7】ApplicationFilterConfig類（org.apache.catalina.core.ApplicationFilterConfig-應(yīng)用過濾器配置類） 1）intro：ApplicationFilterConfig類實(shí)現(xiàn)了 javax.servlet.FilterConfig接口，該類用于管理web 應(yīng)用程序第1次啟動時(shí)創(chuàng)建的所有過濾器實(shí)例； 2）類簽名：final class ApplicationFilterConfig implements FilterConfig? 3）可以通過把一個(gè) org.apache.catalina.Context對象和 一個(gè) FilterDef對象傳遞給 ApplicationFilterConfig類的構(gòu)造函數(shù)來創(chuàng)建一個(gè) ApplicationFilterConfig對象：? public ApplicationFilterConfig(Context context, FilterDef filterDef)throws ClassCastException, ClassNotFoundException,IllegalAccessException, InstantiationException,ServletException {super();this.context = context;setFilterDef(filterDef);} 對以上代碼的分析（Analysis）： A1）Context對象表示一個(gè)web 應(yīng)用程序； A2）FilterDef對象表示一個(gè)過濾器的定義； 4）ApplicationFilterConfig.getFilter()方法：會返回一個(gè) javax.servlet.Filter對象，該方法負(fù)責(zé)載入并實(shí)例化一個(gè)過濾器類；? public String getFilterName() { // org.apache.catalina.core.ApplicationFilterConfig.getFilterName().return (filterDef.getFilterName()); }
【8】ApplicationFilterChain類（org.apache.catalina.core.ApplicationFilterChain） 1）intro：?ApplicationFilterChain類實(shí)現(xiàn)了 javax.servlet.FilterChain接口，StandardWrapperValve.invoke() 方法會創(chuàng)建 ApplicationFilterChain類的一個(gè)實(shí)例，并調(diào)用其 doFilter()方法； 2）Filter接口的doFilter()方法的簽名如下： public interface Filter { // javax.servlet.Filterpublic void init(FilterConfig filterConfig) throws ServletException; public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException; public void destroy(); }3）ApplicationFilterChain.doFilter()方法會將?ApplicationFilterChain 類自身作為第3個(gè)參數(shù)傳遞給過濾器的 doFilter()方法； public void doFilter(ServletRequest request, ServletResponse response) //org.apache.catalina.ApplicationFilterChain.doFileter().throws IOException, ServletException {if( System.getSecurityManager() != null ) {final ServletRequest req = request;final ServletResponse res = response;try {java.security.AccessController.doPrivileged(new java.security.PrivilegedExceptionAction(){public Object run() throws ServletException, IOException {internalDoFilter(req,res);return null;}});} catch( PrivilegedActionException pe) {Exception e = pe.getException();if (e instanceof ServletException)throw (ServletException) e;else if (e instanceof IOException)throw (IOException) e;else if (e instanceof RuntimeException)throw (RuntimeException) e;elsethrow new ServletException(e.getMessage(), e);}} else {internalDoFilter(request,response);}} 4）在Filter.doFilter()方法中， 可以通過顯示地調(diào)用 FileterChain.doFilter()方法來調(diào)用另一個(gè)過濾器。
對以上代碼的分析（Analysis）： A1）正如你所看到的，在doFilter()方法的最后一行會調(diào)用FilterChain.doFilter()方法； A2)如果某個(gè)過濾器時(shí)過濾器鏈中的最后一個(gè)過濾器，則會調(diào)用被請求的 servlet類的 service()方法。如果過濾器沒有調(diào)用chain.doFilter()方法，則不會調(diào)用后面的過濾器；
【9】應(yīng)用程序 0）servlet文件目錄
1）程序源代碼 public final class Bootstrap {public static void main(String[] args) {//invoke: http://localhost:8080/Modern or http://localhost:8080/PrimitiveSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new StandardWrapper();wrapper1.setName("Primitive");wrapper1.setServletClass("servlet.PrimitiveServlet"); // attention for servlet class，要與你的servlet目錄相對應(yīng)；Wrapper wrapper2 = new StandardWrapper();wrapper2.setName("Modern");wrapper2.setServletClass("servlet.ModernServlet"); // attention for servlet class，要與你的servlet目錄相對應(yīng)；Context context = new StandardContext();// StandardContext's start method adds a default mappercontext.setPath("/myApp");context.setDocBase("myApp");LifecycleListener listener = new SimpleContextConfig();((Lifecycle) context).addLifecycleListener(listener);context.addChild(wrapper1);context.addChild(wrapper2);// for simplicity, we don't add a valve, but you can add// valves to context or wrapper just as you did in Chapter 6Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");// add ContextConfig. This listener is important because it configures// StandardContext (sets configured to true), otherwise StandardContext// won't startconnector.setContainer(context);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) context).start();// make the application wait until we press a key.System.in.read();((Lifecycle) context).stop();}catch (Exception e) {e.printStackTrace();}} } 2）打印結(jié)果 E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common. jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/;lib/catalina.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot com.tomca t.chapter11.startup.Bootstrap HttpConnector Opening server socket on all host IP addresses HttpConnector[8080] Starting background thread WebappLoader[/myApp]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\_\myApp StandardManager[/myApp]: Seeding random number generator class java.security.SecureRandom StandardManager[/myApp]: Seeding of random number generator has been completed StandardManager[/myApp]: IOException while loading persisted sessions: java.io.EOFException // // 這是從文件中加載 session對象到內(nèi)存，由于沒有相關(guān)文件，所以加載失敗，拋出異常，但這不會影響我們訪問servlet，大家不要驚慌； java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter11.startup.Bootstrap.main(Bootstrap.java:55) StandardManager[/myApp]: Exception loading sessions from persistent storage java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter11.startup.Bootstrap.main(Bootstrap.java:55) ModernServlet -- init
【1】方法調(diào)用序列 1）對于每個(gè)引入的http 請求，連接器都會調(diào)用與其關(guān)聯(lián)的servlet容器的 invoke() 方法。然后，servlet容器會調(diào)用其所有子容器的invoke() 方法； 2）下圖展示了連接器接收到http 請求后的方法調(diào)用的協(xié)作圖；
3）上圖的具體steps 如下： step1）連接器創(chuàng)建 request 和 response對象； step2）連接器調(diào)用StandardContext.invoke()方法； step3）StandardContext.invoke()方法調(diào)用其管道的invoke() 方法。StandardContext的管道對象的基礎(chǔ)閥是 StandardCoantextValve類的實(shí)例，因此， StandardContext 的管道會調(diào)用 StandardContextValve.invoke()方法； step4）StandardContextValve.invoke()方法 獲取相應(yīng)的Wrapper 實(shí)例處理 http請求，調(diào)用Wrapper實(shí)例的invoke()方法； step5）StandardWrapper類是Wrapper接口的標(biāo)準(zhǔn)實(shí)現(xiàn)，StandardWrapper.invoke()方法 會調(diào)用其管道對象的invoke()方法； step6）StandardWrapper的管道對象中的基礎(chǔ)閥是 StandardWrapperValve 類的實(shí)例，因此，會調(diào)用StandardWrapperValve.invoke()方法，StandardWrapperValve.invoke()方法會調(diào)用Wrapper實(shí)例的 allocate() 方法獲取servlet實(shí)例； step7）allocate()方法調(diào)用load() 方法載入相應(yīng)的servlet類，若已經(jīng)載入，則無需重復(fù)載入； step8）load()方法調(diào)用servlet實(shí)例的init()方法； step9）StandardWrapperValve調(diào)用servlet.service()方法； // Call the filter chain for this request// NOTE: This also calls the servlet's service() methodtry { // org.apache.catalina.core.StandardWrapperValve.invoke()String jspFile = wrapper.getJspFile();if (jspFile != null)sreq.setAttribute(Globals.JSP_FILE_ATTR, jspFile);elsesreq.removeAttribute(Globals.JSP_FILE_ATTR);if ((servlet != null) && (filterChain != null)) {filterChain.doFilter(sreq, sres); // highlight line. doFilter() calls servlet.service()}sreq.removeAttribute(Globals.JSP_FILE_ATTR);} Attention）StandardContext類的構(gòu)造函數(shù)會設(shè)置StandardContextValve類的一個(gè)實(shí)例作為其基礎(chǔ)閥；? public StandardContext() { // org.apache.catalina.core.StardardContextsuper();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this); } Attention）StandardWrapper類的構(gòu)造函數(shù)也會設(shè)置一個(gè) StandardWrapperValve實(shí)例作為其基礎(chǔ)閥： public StandardWrapper() { // org.apache.catalina.core.StardardWrappersuper();swValve=new StandardWrapperValve();pipeline.setBasic(swValve); } 4）依據(jù)上述（3）小節(jié)中的 “處理http 請求的方法調(diào)用協(xié)作圖”，本文按照慣例給出了具體的調(diào)用過程，如下：
4.1）本文第一張是借用了 “tomcat(10)安全性中章節(jié)【6.4】中Supplement-補(bǔ)充模塊”的第2張圖；（for spec info，please visit tomcat(10)安全性），這旨在說明從HttpConnector -> StandardContext.invoke() -> StandardPipeline.invoke()的調(diào)用過程；
4.2）本文接著上面的調(diào)用過程繼續(xù)分析，調(diào)用過程如下圖；旨在說明? StandardPipeline.invoke() -> StandardContextValve.invoke() -> StandardWrapper.invoke() -> StandardPipeline.invoke() -> StandardWrapperValve.invoke() -> ApplicationFilterChain().doFilter()? ->?ApplicationFilterChain().internalDoFilter() -> HttpServlet(ModernServlet).service() -> ModernServlet->doGet() 的調(diào)用過程.（Bingo）
對上述協(xié)作圖和詳細(xì)調(diào)用過程圖的分析（Analysis）： A0）要知道Tomcat中有4種容器：Engine，Host，Context 和 Wrapper；（干貨——本文一直強(qiáng)調(diào)這一點(diǎn)，理解容器的層次結(jié)構(gòu)對于理解tomcat非常重要） A1）StandardContext 和 StandardWrapper 都是容器：他們都繼承自 ContainerBase，只不過StandardWrapper是StandardContext的子容器，而StandardWrapper是最小的容器，即它沒有子容器； A2）下面分別看StandardWrapper，StandardContext的構(gòu)造函數(shù)?和 ContainerBase 的變量定義； public final class StandardWrapper extends ContainerBase implements ServletConfig, Wrapper {public StandardWrapper() {super();swValve=new StandardWrapperValve();pipeline.setBasic(swValve);} } public class StandardContext extends ContainerBase implements Context {public StandardContext() { super();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this);} } public abstract class ContainerBase implements Container, Lifecycle, Pipeline {protected Pipeline pipeline = new StandardPipeline(this); // highlight line.protected HashMap children = new HashMap();protected int debug = 0; protected LifecycleSupport lifecycle = new LifecycleSupport(this); protected ArrayList listeners = new ArrayList(); protected Loader loader = null; protected Logger logger = null; protected Manager manager = null; protected Cluster cluster = null; protected Mapper mapper = null; protected HashMap mappers = new HashMap(); protected String mapperClass = null; protected String name = null; protected Container parent = null; protected ClassLoader parentClassLoader = null; protected Pipeline pipeline = new StandardPipeline(this); protected Realm realm = null; protected DirContext resources = null; protected static StringManager sm = StringManager.getManager(Constants.Package); protected boolean started = false; protected PropertyChangeSupport support = new PropertyChangeSupport(this); } A3）可以看到 父容器ContainerBase定義了管道StandardPipeline，而子容器StandardContext 設(shè)置StandardContextValve為基礎(chǔ)閥；而最小的容器StandardWrapper設(shè)置StandardWrapperValve為基礎(chǔ)閥； A4）也即 StandardContext 和?StandardWrapper 共用同一個(gè)管道，分別設(shè)置不同的基礎(chǔ)閥；（當(dāng)然，可以分別設(shè)置非基礎(chǔ)閥，非基礎(chǔ)閥在基礎(chǔ)閥被調(diào)用之前調(diào)用）；
【2】SingleThreadModel（已經(jīng)被棄用了） 1）intro：servlet類可以實(shí)現(xiàn) javax.servlet.SingleThreadModel 接口，這樣的servlet類也稱為 SingleThreadModel（STM）servlet類。根據(jù)servlet規(guī)范，實(shí)現(xiàn)此接口的目的是保證 servlet實(shí)例一次只處理一個(gè)請求； Attention）若 servlet類實(shí)現(xiàn) SingleThreadModel接口，則可以保證絕不會有兩個(gè)線程同時(shí)執(zhí)行該servlet.service()方法。這一點(diǎn)由 servlet容器通過控制對單一 servlet實(shí)例的同步訪問實(shí)現(xiàn)，或者維護(hù)一個(gè) servlet實(shí)例池，然后將每個(gè)新請求分派給一個(gè)空閑的servlet實(shí)例。該接口并不能防止servlet訪問共享資源造成的同步問題，例如訪問類的靜態(tài)變量或訪問servlet作用域之外的類； （干貨——有很多程序員哥哥沒有讀懂這段話，想當(dāng)然的認(rèn)為，實(shí)現(xiàn)了該接口的servlet就是線程安全的。這種想法是錯誤的，請?jiān)俣纫槐樯厦娴囊膬?nèi)容（原文作者說的，哈哈））
2）事實(shí)上，實(shí)現(xiàn)了 SingleThreadModel 接口的servlet類只能保證在同一時(shí)刻，只有一個(gè)線程在執(zhí)行該 servlet實(shí)例的service()方法。但，為了提高執(zhí)行 性能，servlet容器會創(chuàng)建多個(gè)STM servlet實(shí)例。也就是說，STM servlet.service()方法 會在多個(gè)STM?servlet實(shí)例中并發(fā)執(zhí)行。如果servlet實(shí)例需要靜態(tài)類變量或類外的某些資源的話，就有可能引起同步問題； Atttention）在servlet 2.4中，SingleThreadModel接口已經(jīng)被棄用了，因?yàn)樗鼤?servlet程序員誤以為該接口的servlet類就是多線程安全的；
【3】StandardWrapper 1）intro to?StandardWrapper：其主要任務(wù)是 載入它所代表的servlet類，并進(jìn)行實(shí)例化； 2）StandardWrapper并不調(diào)用servlet的service方法，該任務(wù)由 StandardWrapperValve對象（StandardWrapper實(shí)例的管道對象中的基礎(chǔ)閥）完成； 3）StandardWrapperValve對象通過調(diào)用allocate()方法從 StandardWrapper實(shí)例中獲取servlet實(shí)例，在獲得servlet實(shí)例后，StandardWrapperValve實(shí)例就會調(diào)用servlet實(shí)例的service()方法； 【3.1】分配servlet實(shí)例? 1）分配servlet實(shí)例是由 StandardWrapper.allocate()方法來完成的（allocate方法返回請求的servelt實(shí)例）； 2）allocate()方法分為兩部分（parts）： p1）第一部分：?allocate()首先檢查 instance是否為null，若是， 則allocate()方法調(diào)用 loadServlet()方法載入相關(guān)的servlet類，然后 整型變量countAllocated加1，返回instance的值； p2）第二部分： p2.1）若StandardWrapper表示的servlet是一個(gè)STM servlet類，則allocate()會試圖從對象池中返回一個(gè)servlet實(shí)例。變量 instancePool 是一個(gè) java.util.Stack類型的棧，其中保存了所有的STM servlet實(shí)例： private Stack instancePool = null; p2.2）只要STM servlet實(shí)例數(shù)不超過指定的最大值，allocate()方法會返回一個(gè) STM servlet實(shí)例。整型變量maxInstances 保存了在棧中存儲的 STM servlet實(shí)例的最大值，default value = 20； private int maxInstances = 20; p2.3）而 nInstances 保存了當(dāng)前 STM servlet實(shí)例的數(shù)量（初始為0）；
3）源碼如下
public Servlet allocate() throws ServletException { //org.apache.catalina.core.StandardWrapper.allocate() // part 1 begins.if (debug >= 1) log("Allocating an instance");// If we are currently unloading this servlet, throw an exceptionif (unloading)throw new ServletException(sm.getString("standardWrapper.unloading", getName()));// If not SingleThreadedModel, return the same instance every timeif (!singleThreadModel) {// Load and initialize our instance if necessaryif (instance == null) {synchronized (this) {if (instance == null) {try {instance = loadServlet();} catch (ServletException e) {throw e;} catch (Throwable e) {throw new ServletException(sm.getString("standardWrapper.allocate"), e);}}}}if (!singleThreadModel) {if (debug >= 2)log(" Returning non-STM instance");countAllocated++;return (instance);}} // part1 ends. // part2 starts.synchronized (instancePool) {while (countAllocated >= nInstances) {// Allocate a new instance if possible, or else waitif (nInstances < maxInstances) {try {instancePool.push(loadServlet());nInstances++;} catch (ServletException e) {throw e;} catch (Throwable e) {throw new ServletException(sm.getString("standardWrapper.allocate"), e);}} else {try {instancePool.wait();} catch (InterruptedException e) {;}}}if (debug >= 2)log(" Returning allocated STM instance");countAllocated++;return (Servlet) instancePool.pop();}}// part2 ends. 【3.2】載入servlet類 1）StandardWrapper類實(shí)現(xiàn)了Wrapper接口的 load() 方法，load() 方法調(diào)用loadServlet()方法載入某個(gè)servlet類，并調(diào)用其 init() 方法，此時(shí)要傳入一個(gè) javax.servlet.ServletConfig實(shí)例作為參數(shù)； 2）loadServlet() 方法是如何工作的 public synchronized void load() throws ServletException { // org.apache.catalina.core.StandardWrapper.load()instance = loadServlet(); }public synchronized Servlet loadServlet() throws ServletException { // org.apache.catalina.core.StandardWrapper.loadServlet()// Nothing to do if we already have an instance or an instance poolif (!singleThreadModel && (instance != null))return instance;PrintStream out = System.out;if (swallowOutput) {SystemLogHandler.startCapture();}Servlet servlet = null;try {// If this "servlet" is really a JSP file, get the right class.// HOLD YOUR NOSE - this is a kludge that avoids having to do special// case Catalina-specific code in Jasper - it also requires that the// servlet path be replaced by the <jsp-file> element content in// order to be completely effectiveString actualClass = servletClass;if ((actualClass == null) && (jspFile != null)) {Wrapper jspWrapper = (Wrapper)((Context) getParent()).findChild(Constants.JSP_SERVLET_NAME);if (jspWrapper != null)actualClass = jspWrapper.getServletClass();}// Complain if no servlet class has been specifiedif (actualClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.notClass", getName()));} // Acquire an instance of the class loader to be usedLoader loader = getLoader();if (loader == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingLoader", getName()));} ClassLoader classLoader = loader.getClassLoader(); // Special case class loader for a container provided servletif (isContainerProvidedServlet(actualClass)) {classLoader = this.getClass().getClassLoader();log(sm.getString("standardWrapper.containerServlet", getName()));} // Load the specified servlet class from the appropriate class loaderClass classClass = null;try {if (classLoader != null) {classClass = classLoader.loadClass(actualClass);} else {classClass = Class.forName(actualClass);}} catch (ClassNotFoundException e) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass),e);}if (classClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass));} // Instantiate and initialize an instance of the servlet class itselftry {servlet = (Servlet) classClass.newInstance();} catch (ClassCastException e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.notServlet", actualClass), e);} catch (Throwable e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.instantiate", actualClass), e);} // Check if loading the servlet in this web application should be// allowedif (!isServletAllowed(servlet)) {throw new SecurityException(sm.getString("standardWrapper.privilegedServlet",actualClass));} // Special handling for ContainerServlet instancesif ((servlet instanceof ContainerServlet) &&isContainerProvidedServlet(actualClass)) {((ContainerServlet) servlet).setWrapper(this);} // Call the initialization method of this servlettry {instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_INIT_EVENT,servlet);servlet.init(facade);// Invoke jspInit on JSP pagesif ((loadOnStartup >= 0) && (jspFile != null)) {// Invoking jspInitHttpRequestBase req = new HttpRequestBase();HttpResponseBase res = new HttpResponseBase();req.setServletPath(jspFile);req.setQueryString("jsp_precompile=true");servlet.service(req, res);}instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet);} catch (UnavailableException f) {instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet, f);unavailable(f);throw f;} catch (ServletException f) {instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet, f);// If the servlet wanted to be unavailable it would have// said so, so do not call unavailable(null).throw f;} catch (Throwable f) {instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet, f);// If the servlet wanted to be unavailable it would have// said so, so do not call unavailable(null).throw new ServletException(sm.getString("standardWrapper.initException", getName()), f);} // Register our newly initialized instancesingleThreadModel = servlet instanceof SingleThreadModel;if (singleThreadModel) {if (instancePool == null)instancePool = new Stack();}fireContainerEvent("load", this);} finally {if (swallowOutput) {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {if (getServletContext() != null) {getServletContext().log(log);} else {out.println(log);}}}}return servlet;}
step1）檢查當(dāng)前的StandardWrapper類是否表示的是一個(gè) STM servlet類，若不是，且變量instance不為null（表示以前已經(jīng)載入過這個(gè)servlet），它就直接返回該實(shí)例； // Nothing to do if we already have an instance or an instance poolif (!singleThreadModel && (instance != null))return instance; step2）獲得 System.out 和 System.err 的輸出，便于它使用 javax.servlet.ServletConfig.log() 方法記錄日志消息： PrintStream out = System.out;if (swallowOutput) {SystemLogHandler.startCapture();} step3）定義類型為javax.servlet.Servlet 名為servlet 的變量，其表示已載入的servlet實(shí)例，會由 loadServlet()方法返回； Servlet servlet = null; step4）由于Catalina是一個(gè)JSP容器，故loadServlet()方法必須檢查請求的servlet是不是一個(gè)jsp 頁面。若是，則loadServlet() 方法需要獲取代表該jsp 頁面的實(shí)際servlet類； String actualClass = servletClass;if ((actualClass == null) && (jspFile != null)) {Wrapper jspWrapper = (Wrapper)((Context) getParent()).findChild(Constants.JSP_SERVLET_NAME);if (jspWrapper != null)actualClass = jspWrapper.getServletClass(); } // public static final String JSP_SERVLET_NAME = "jsp";<span style="font-family: SimSun; line-height: 1.5; background-color: inherit;">? ? ? ? ? ?</span> step5）如果找不到該jsp 頁面的servlet類，則會使用變量 servletClass（actualClass）的值。若沒有調(diào)用StandardWrapper.serServletClass() 方法設(shè)置servletClass的值，則會拋出異常，并停止執(zhí)行后續(xù)方法； // Complain if no servlet class has been specifiedif (actualClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.notClass", getName()));}<span style="font-family: SimSun; background-color: rgb(255, 255, 255);">? ? ? ? ? ?</span> step6）這時(shí)，要載入的servlet類名已經(jīng)解析完了，loadServlet()方法會獲取載入器 Loader loader = getLoader();public Loader getLoader() { // org.apache.catalina.core.ContainerBase.getLoader();if (loader != null)return (loader);if (parent != null)return (parent.getLoader());return (null);} step7）若找到載入器（loader），則loadServlet()方法調(diào)用getClassLoader()方法獲取一個(gè)ClassLoader； ClassLoader classLoader = loader.getClassLoader(); step8）Catalina提供了一些用于訪問servlet容器內(nèi)部數(shù)據(jù)的專用servlet類。如果某個(gè)servlet類是這種專用的servlet，即若isContainerProvidedServlet()方法返回true，則變量 classLoader被賦值為另一種ClassLoader實(shí)例，如此一來，這個(gè)servlet實(shí)例就可以訪問Catalina的內(nèi)部數(shù)據(jù)了； // Special case class loader for a container provided servletif (isContainerProvidedServlet(actualClass)) {classLoader = this.getClass().getClassLoader();log(sm.getString("standardWrapper.containerServlet", getName()));} step9）準(zhǔn)備好類載入器和準(zhǔn)備載入的servlet類名后，loadServlet()方法就可以載入servlet類了； // Load the specified servlet class from the appropriate class loaderClass classClass = null;try {if (classLoader != null) {classClass = classLoader.loadClass(actualClass);} else {classClass = Class.forName(actualClass);}} catch (ClassNotFoundException e) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass),e);} if (classClass == null) {unavailable(null);throw new ServletException(sm.getString("standardWrapper.missingClass", actualClass));} step10）實(shí)例化該servlet ? ? ? // Instantiate and initialize an instance of the servlet class itselftry {servlet = (Servlet) classClass.newInstance();} catch (ClassCastException e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.notServlet", actualClass), e);} catch (Throwable e) {unavailable(null);// Restore the context ClassLoaderthrow new ServletException(sm.getString("standardWrapper.instantiate", actualClass), e);}
step11）在loadServlet()方法實(shí)例化這個(gè)servlet之前，它會調(diào)用 isServletAllowed()方法檢查該servlet 類是否允許載入：? ? ? // Check if loading the servlet in this web application should be// allowedif (!isServletAllowed(servlet)) {throw new SecurityException(sm.getString("standardWrapper.privilegedServlet",actualClass));}
step12）若通過了安全檢查，它還會繼續(xù)檢查該servlet類是否是一個(gè) ContainerServlet類型的servlet（實(shí)現(xiàn)了 org.apache.catalina.ContainerServlet接口的 servlet可以訪問Catalina的內(nèi)部功能）。若該servlet類是一個(gè) ContainerServlet，loadServlet()方法會調(diào)用 ContainerServlet.setWrapper()，傳入StandardWrapper實(shí)例；? // Special handling for ContainerServlet instancesif ((servlet instanceof ContainerServlet) &&isContainerProvidedServlet(actualClass)) {((ContainerServlet) servlet).setWrapper(this);} step13）觸發(fā)BEFORE_INIT_EVENT事件，調(diào)用servlet實(shí)例的 init()方法（init()方法傳入了javax.servlet.ServletConfig外觀對象）：? // Call the initialization method of this servlettry {instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_INIT_EVENT,servlet);servlet.init(facade); // highlight line. step14）若變量 loadOnStartup 大于0， 且被請求的servlet類實(shí)際上是一個(gè)jsp 頁面，則servlet實(shí)例的service()方法；? if ((loadOnStartup >= 0) && (jspFile != null)) {// Invoking jspInitHttpRequestBase req = new HttpRequestBase();HttpResponseBase res = new HttpResponseBase();req.setServletPath(jspFile);req.setQueryString("jsp_precompile=true");servlet.service(req, res); // highlight line.}instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT,servlet); step15）觸發(fā)AFTER_INIT_EVENT事件 instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT, step16）若StandardWrapper對象表示的servlet類是一個(gè)STM servlet，則將該servlet實(shí)例添加到servlet實(shí)例池中。因此會判斷 instancePool 是否為null，若是，則要給他賦值一個(gè)Stack 對象；? // Register our newly initialized instancesingleThreadModel = servlet instanceof SingleThreadModel;if (singleThreadModel) {if (instancePool == null)instancePool = new Stack(); // highlight line. } step17）在finally代碼塊中，loadServlet()方法停止捕獲System.out 和 System.err 對象，記錄在載入 ServletContext.log()方法的過程中產(chǎn)生的日志消息； finally {if (swallowOutput) {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {if (getServletContext() != null) {getServletContext().log(log); // highlight line.} else {out.println(log);}}}} public ServletContext getServletContext() { org.apache.catalina.core.StandardWrapper.getServletContext()if (parent == null)return (null);else if (!(parent instanceof Context))return (null);elsereturn (((Context) parent).getServletContext());} step18）最后返回已載入的servlet實(shí)例； return servlet; 【3.3】ServletConfig對象 1）intro：在上述step13）中提到了 servlet.init(facade)，而facade 是 javax.servlet.ServletConfig對象的一個(gè)外觀變量； 2）StandardWrapper對象是如何獲取 servletConfig 對象的？答案就在 StandardWrapper中，該類不僅實(shí)現(xiàn)了 Wrapper接口，還實(shí)現(xiàn)了 javax.servlet.ServletConfig 接口； public final class StandardWrapper extends ContainerBase implements ServletConfig, Wrapper { // org.apache.catalina.core.StandardWrapper // ...... } public interface ServletConfig { // javax.servlet.ServletConfig public String getServletName();public ServletContext getServletContext(); public String getInitParameter(String name);public Enumeration getInitParameterNames(); } 3）javax.servlet.ServletConfig 接口有4個(gè)方法：getServletContext() , getServletName(), ?getInitParameter()， ?getInitParameterNames()方法；下面對這4個(gè)方法進(jìn)行說明； method1）getServletConfig()方法： public ServletContext getServletContext() { // org.apache.catalina.core.StandardWrapper.getServletContext()if (parent == null)return (null);else if (!(parent instanceof Context))return (null);elsereturn (((Context) parent).getServletContext());}/*** Return the servlet context for which this Context is a facade.*/public ServletContext getServletContext() { // org.apache.catalina.core.StandardContext.getServletContext()if (context == null)context = new ApplicationContext(getBasePath(), this);return (context);} Attention）正如以上代碼所展示的那樣，無法單獨(dú)使用一個(gè)Wrapper實(shí)例來表示一個(gè) servlet 類的定義。Wrapper 實(shí)例必須駐留在某個(gè) Context 容器中，這樣，當(dāng)調(diào)用其父容器的getServletConfig()方法時(shí)，才能返回ServletContext類的一個(gè)實(shí)例； method2）getServletName()方法：該方法返回 servlet類的名字，該方法的簽名如下： ?public String getServletName() { // org.apache.catalina.core.StandardWrapper.getServletName()return (getName());} public String getName() { // org.apache.catalina.core.ContainerBase.getName(). // 因?yàn)?public final class StandardWrapper extends ContainerBasereturn (name);} method3）getInitParameter()方法：該方法返回指定初始參數(shù)的值 public String getInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.getInitParameter()return (findInitParameter(name));} public String findInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.findInitParameter()synchronized (parameters) {return ((String) parameters.get(name));}} 對getInitParameter（）方法的分析（Analysis）： A1）在StandardWrapper類中，初始化參數(shù) parameters 存儲在一個(gè) HashMap類型中； private HashMap parameters = new HashMap(); A2）通過addInitParameter()方法，傳入?yún)?shù)的名字 和 對應(yīng)的值 來填充變量 parameters 的值： public void addInitParameter(String name, String value) { // org.apache.catalina.core.StandardWrapper.addInitParameter().synchronized (parameters) {parameters.put(name, value);}fireContainerEvent("addInitParameter", name); // highlight line.} public void fireContainerEvent(String type, Object data) {// org.apache.catalina.core.ContainerBase.fireContainerEvent().if (listeners.size() < 1)return;ContainerEvent event = new ContainerEvent(this, type, data);ContainerListener list[] = new ContainerListener[0];synchronized (listeners) {list = (ContainerListener[]) listeners.toArray(list);}for (int i = 0; i < list.length; i++)((ContainerListener) list[i]).containerEvent(event);} A3）StandardWrapper.getInitParameter()方法的實(shí)現(xiàn)如下：? public String getInitParameter(String name) {return (findInitParameter(name));} A4）findInitParameter()方法接收一個(gè)指定的初始化參數(shù)名的字符串變量，調(diào)用HashMap 變量 parameters的get()方法獲取初始化參數(shù)的值； public String findInitParameter(String name) { // org.apache.catalina.core.StandardWrapper.findInitParameter()synchronized (parameters) {return ((String) parameters.get(name)); // highlight line.}} method4）getInitParameterNames()方法： 該方法返回所有初始化參數(shù)的名字的集合，實(shí)際上是 java.util.Enumeration的實(shí)例；? public Enumeration getInitParameterNames() {synchronized (parameters) {return (new Enumerator(parameters.keySet()));}} 【3.4】servlet容器的父子關(guān)系 1）intro to StandardWrapper：Wrapper實(shí)例代表一個(gè)servlet實(shí)例，是最低級的容器，故Wrapper不能再有子容器，不應(yīng)該調(diào)用addChild()方法添加子容器，否則拋出 java.lang.IllegalStateException 異常；（干貨review——Wrapper實(shí)例代表一個(gè)servlet實(shí)例，是最低級的容器，故Wrapper不能再有子容器） 2）org.apache.catalina.core.StandardWrapper.addChild()方法實(shí)現(xiàn)如下： public void addChild(Container child) {throw new IllegalStateException (sm.getString("standardWrapper.notChild"));} Attention）Wrapper容器的父容器只能是 Context 容器；若我們在設(shè)置父容器的時(shí)候，傳入了非Context容器，則拋出 java.lang.IllegalArgumentException 異常； public void setParent(Container container) { // org.apache.catalina.core.StandardWrapper.setParent().if ((container != null) && !(container instanceof Context)) throw new IllegalArgumentException(sm.getString("standardWrapper.notContext"));if (container instanceof StandardContext) {swallowOutput = ((StandardContext)container).getSwallowOutput();}super.setParent(container); // highlight line.} public void setParent(Container container) { // org.apache.catalina.core.ContainerBase.setParent().Container oldParent = this.parent;this.parent = container;support.firePropertyChange("parent", oldParent, this.parent);}
【4】 StandardWrapperFacade類?（干貨——應(yīng)用了設(shè)計(jì)模式中的外觀模式） 1）problem+solution： 1.1）problem：StandardWrapper實(shí)例會調(diào)用它所載入的servlet類的實(shí)例的init()方法。init()方法需要一個(gè)javax.servlet.ServletConfig 實(shí)例，而StandardWrapper了本身也實(shí)現(xiàn)了 javax.servlet.ServletConfig 接口，所以，理論上 StandardWrapper需要將其中大部分公共方法對servlet程序員隱藏起來； 1.2）solution：為了實(shí)現(xiàn)這個(gè)目的，StandardWrapper類將自身實(shí)例包裝成 StandardWrapperFacade類的一個(gè)實(shí)例；
2）StandardWrapper類創(chuàng)建StandardWrapperFacade對象，并將自身作為參數(shù)傳入StandardWrapperFacade的構(gòu)造器； private StandardWrapperFacade facade = new StandardWrapperFacade(this); // defined in StandardWrapper.java 3）StandardWrapperFacade的構(gòu)造函數(shù)； public StandardWrapperFacade(StandardWrapper config) {super();this.config = (ServletConfig) config; // private ServletConfig config = null;} 4）因此當(dāng)創(chuàng)建StandardWrapper對象調(diào)用servlet實(shí)例的 init()方法時(shí)，它會傳入StandardWrapperFacade類的一個(gè)實(shí)例。這樣，在servlet實(shí)例內(nèi)調(diào)用 ServletConfig.getServletName(),ServletConfig.getInitParameter(), getInitParameterNames() ，getServletContext()方法會直接傳遞給 StandardWrapper類的相應(yīng)方法； 5）org.apache.catalina.core.StandardWrapperFacade 的定義如下： public final class StandardWrapperFacade implements ServletConfig {public StandardWrapperFacade(StandardWrapper config) {super();this.config = (ServletConfig) config;}public String getServletName() {return config.getServletName();}public ServletContext getServletContext() {ServletContext theContext = config.getServletContext();if ((theContext != null) &&(theContext instanceof ApplicationContext))theContext = ((ApplicationContext) theContext).getFacade();return (theContext);}public String getInitParameter(String name) {return config.getInitParameter(name);}public Enumeration getInitParameterNames() {return config.getInitParameterNames();} }
【5】StandardWrapperValve類 1）StandardWrapperValve類是 StandardWrapper實(shí)例中的基礎(chǔ)閥，要完成兩個(gè)操作（Operations）： public StandardWrapper() { // StandardWrapper的構(gòu)造函數(shù)；super();swValve=new StandardWrapperValve();pipeline.setBasic(swValve);} O1）執(zhí)行與該servlet實(shí)例關(guān)聯(lián)的全部過濾器；（干貨——這里引入了過濾器） O2）調(diào)用servlet實(shí)例的service()方法； 2）完成上述任務(wù)后，在 StandardWrapperValve.invoke()方法實(shí)現(xiàn)中會執(zhí)行以下操作（Operations）： O1）調(diào)用StandardWrapper.allocate()方法獲取該StandardWrapper實(shí)例所表示的 servlet實(shí)例； public void invoke(Request request, Response response,ValveContext valveContext)throws IOException, ServletException {long t1=System.currentTimeMillis();requestCount++;// Initialize local variables we may needboolean unavailable = false;Throwable throwable = null;StandardWrapper wrapper = (StandardWrapper) getContainer();ServletRequest sreq = request.getRequest();ServletResponse sres = response.getResponse();Servlet servlet = null;HttpServletRequest hreq = null;if (sreq instanceof HttpServletRequest)hreq = (HttpServletRequest) sreq;HttpServletResponse hres = null;if (sres instanceof HttpServletResponse)hres = (HttpServletResponse) sres;// Check for the application being marked unavailableif (!((Context) wrapper.getParent()).getAvailable()) {hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,sm.getString("standardContext.isUnavailable"));unavailable = true;}// Check for the servlet being marked unavailableif (!unavailable && wrapper.isUnavailable()) {log(sm.getString("standardWrapper.isUnavailable",wrapper.getName()));if (hres == null) {; // NOTE - Not much we can do generically} else {long available = wrapper.getAvailable();if ((available > 0L) && (available < Long.MAX_VALUE))hres.setDateHeader("Retry-After", available);hres.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,sm.getString("standardWrapper.isUnavailable",wrapper.getName()));}unavailable = true;}// Allocate a servlet instance to process this requesttry {if (!unavailable) {servlet = wrapper.allocate(); // highlight line.} // ...... O2）調(diào)用私有方法 createFilterChain()，創(chuàng)建過濾器鏈； // Create the filter chain for this request ApplicationFilterChain filterChain = createFilterChain(request, servlet); // for create FilterChain方法，本章節(jié)末尾； private ApplicationFilterChain createFilterChain(Request request, Servlet servlet) { if (servlet == null)return (null);ApplicationFilterChain filterChain = new ApplicationFilterChain(); filterChain.setServlet(servlet);StandardWrapper wrapper = (StandardWrapper) getContainer();filterChain.setSupport(wrapper.getInstanceSupport());// Acquire the filter mappings for this ContextStandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();// If there are no filter mappings, we are doneif ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// Acquire the information we will need to match filter mappingsString requestPath = null;if (request instanceof HttpRequest) {HttpServletRequest hreq =(HttpServletRequest) request.getRequest();String contextPath = hreq.getContextPath();if (contextPath == null)contextPath = "";String requestURI = ((HttpRequest) request).getDecodedRequestURI();if (requestURI.length() >= contextPath.length())requestPath = requestURI.substring(contextPath.length());}String servletName = wrapper.getName();int n = 0;// Add the relevant path-mapped filters to this filter chainfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersURL(filterMaps[i], requestPath))continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}// Add filters that match on servlet name secondfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersServlet(filterMaps[i], servletName))continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}return (filterChain);} O3）調(diào)用過濾器鏈的 doFilter()方法，其中包括調(diào)用servlet實(shí)例的service()方法； try {String jspFile = wrapper.getJspFile();if (jspFile != null)sreq.setAttribute(Globals.JSP_FILE_ATTR, jspFile);elsesreq.removeAttribute(Globals.JSP_FILE_ATTR);if ((servlet != null) && (filterChain != null)) {filterChain.doFilter(sreq, sres); // hightlight line.}sreq.removeAttribute(Globals.JSP_FILE_ATTR); // ......public void doFilter(ServletRequest request, ServletResponse response) //org.apache.catlina.core.ApplicationFilterChain.doFileter()throws IOException, ServletException {if( System.getSecurityManager() != null ) {final ServletRequest req = request;final ServletResponse res = response;try {java.security.AccessController.doPrivileged(new java.security.PrivilegedExceptionAction(){public Object run() throws ServletException, IOException {internalDoFilter(req,res); // highlight line. internalDoFilter() 參見文末.return null;}});} catch( PrivilegedActionException pe) {Exception e = pe.getException();if (e instanceof ServletException)throw (ServletException) e;else if (e instanceof IOException)throw (IOException) e;else if (e instanceof RuntimeException)throw (RuntimeException) e;elsethrow new ServletException(e.getMessage(), e);}} else {internalDoFilter(request,response);}} private void internalDoFilter(ServletRequest request, ServletResponse response)throws IOException, ServletException { //org.apache.catalina.core.ApplicationFilterChain.internalDoFilter().// Construct an iterator the first time this method is calledif (this.iterator == null)this.iterator = filters.iterator();// Call the next filter if there is oneif (this.iterator.hasNext()) {ApplicationFilterConfig filterConfig =(ApplicationFilterConfig) iterator.next();Filter filter = null;try {filter = filterConfig.getFilter();support.fireInstanceEvent(InstanceEvent.BEFORE_FILTER_EVENT,filter, request, response);filter.doFilter(request, response, this);support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,filter, request, response);} //......return;}// We fell off the end of the chain -- call the servlet instancetry {support.fireInstanceEvent(InstanceEvent.BEFORE_SERVICE_EVENT,servlet, request, response);if ((request instanceof HttpServletRequest) &&(response instanceof HttpServletResponse)) { servlet.service((HttpServletRequest) request, (HttpServletResponse) response); // 這不就是你夢寐以求的service()方法嗎？哈哈。} else {servlet.service(request, response); // and this highlight line.}support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,servlet, request, response);} //......} O4）釋放過濾器鏈； try {if (filterChain != null)filterChain.release(); // highlight line.} catch (Throwable e) {log(sm.getString("standardWrapper.releaseFilters",wrapper.getName()), e);if (throwable == null) {throwable = e;exception(request, response, e);}} void release() { //org.apache.catalina.core.ApplicationFilterChain.release()this.filters.clear();this.iterator = iterator;this.servlet = null;} O5）調(diào)用Wrapper實(shí)例的 deallocate()方法； // Deallocate the allocated servlet instancetry {if (servlet != null) {wrapper.deallocate(servlet); // highlight line.}} catch (Throwable e) {log(sm.getString("standardWrapper.deallocateException",wrapper.getName()), e);if (throwable == null) {throwable = e;exception(request, response, e);}}public void deallocate(Servlet servlet) throws ServletException { //org.apache.catalina.core.StandardWrapper.deallocate()// If not SingleThreadModel, no action is requiredif (!singleThreadModel) {countAllocated--;return;}synchronized (instancePool) {countAllocated--;instancePool.push(servlet);instancePool.notify();}} O6）若該servlet類再也不會被使用到，調(diào)用Wrapper實(shí)例的unload()方法； // If this servlet has been marked permanently unavailable,// unload it and release this instancetry {if ((servlet != null) &&(wrapper.getAvailable() == Long.MAX_VALUE)) {wrapper.unload(); // highlight line.}} // ......long t2=System.currentTimeMillis();long time=t2-t1;processingTime+=time;if( time > maxTime ) maxTime=time;} Attention）以上調(diào)用過程中，最重要的是對 createFilterChain()方法和過濾器鏈的 doFilter()方法的調(diào)用。createFilterChain()方法創(chuàng)建一個(gè) ApplicationFilterChain實(shí)例，并將所有需要應(yīng)用到該Wrapper實(shí)例所代表的servlet實(shí)例的過濾器添加到其中； private ApplicationFilterChain createFilterChain(Request request,Servlet servlet) {if (servlet == null)return (null);ApplicationFilterChain filterChain =new ApplicationFilterChain();filterChain.setServlet(servlet);StandardWrapper wrapper = (StandardWrapper) getContainer();filterChain.setSupport(wrapper.getInstanceSupport());StandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();if ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// Acquire the information we will need to match filter mappingsString requestPath = null;if (request instanceof HttpRequest) {HttpServletRequest hreq =(HttpServletRequest) request.getRequest();String contextPath = hreq.getContextPath();if (contextPath == null)contextPath = "";String requestURI = ((HttpRequest) request).getDecodedRequestURI();if (requestURI.length() >= contextPath.length())requestPath = requestURI.substring(contextPath.length());}String servletName = wrapper.getName();int n = 0; // Add the relevant path-mapped filters to this filter chainfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersURL(filterMaps[i], requestPath)) continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue; }filterChain.addFilter(filterConfig); n++;}// Add filters that match on servlet name secondfor (int i = 0; i < filterMaps.length; i++) {if (!matchFiltersServlet(filterMaps[i], servletName)) continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {continue;}filterChain.addFilter(filterConfig);n++;}return (filterChain); } public synchronized void unload() throws ServletException {if (!singleThreadModel && (instance == null))return;unloading = true;if (countAllocated > 0) {int nRetries = 0;while (nRetries < 10) {if (nRetries == 0) {log("Waiting for " + countAllocated +" instance(s) to be deallocated");}try {Thread.sleep(50);} catch (InterruptedException e) {;}nRetries++;}}ClassLoader oldCtxClassLoader =Thread.currentThread().getContextClassLoader();ClassLoader classLoader = instance.getClass().getClassLoader();PrintStream out = System.out;if (swallowOutput) {SystemLogHandler.startCapture();}try {instanceSupport.fireInstanceEvent(InstanceEvent.BEFORE_DESTROY_EVENT, instance);Thread.currentThread().setContextClassLoader(classLoader);instance.destroy();instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_DESTROY_EVENT, instance);} catch (Throwable t) {instanceSupport.fireInstanceEvent(InstanceEvent.AFTER_DESTROY_EVENT, instance, t);instance = null;instancePool = null;nInstances = 0;fireContainerEvent("unload", this);unloading = false;throw new ServletException(sm.getString("standardWrapper.destroyException", getName()),t);} finally {Thread.currentThread().setContextClassLoader(oldCtxClassLoader);if (swallowOutput) {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {if (getServletContext() != null) {getServletContext().log(log);} else {out.println(log);}}}}instance = null;if (singleThreadModel && (instancePool != null)) {try {Thread.currentThread().setContextClassLoader(classLoader);while (!instancePool.isEmpty()) {((Servlet) instancePool.pop()).destroy();}} catch (Throwable t) {instancePool = null;nInstances = 0;unloading = false;fireContainerEvent("unload", this);throw new ServletException(sm.getString("standardWrapper.destroyException",getName()), t);} finally {Thread.currentThread().setContextClassLoader(oldCtxClassLoader);}instancePool = null;nInstances = 0;}singleThreadModel = false;unloading = false;fireContainerEvent("unload", this); }
【6】 FilterDef類（org.apache.catalina.deploy.FilterDef） 1）intro：FilterDef 是一個(gè)過濾器的定義； 2）FilterDef類中的每個(gè)屬性表示在定義filter元素時(shí)聲明的子元素。其中Map 類型的變量parameters 存儲了初始化過濾器時(shí)所需要的所有參數(shù)。addInitParameter()方法用于向parameters 中添加新的 name/value 形式的參數(shù)名和對應(yīng)的值； 3）其定義源碼如下： public final class FilterDef { // org.apache.catalina.deploy.FilterDef private String description = null;public String getDescription() {return (this.description);}public void setDescription(String description) {this.description = description;} private String displayName = null;public String getDisplayName() {return (this.displayName);}public void setDisplayName(String displayName) {this.displayName = displayName;}private String filterClass = null;public String getFilterClass() {return (this.filterClass);}public void setFilterClass(String filterClass) {this.filterClass = filterClass;} private String filterName = null;public String getFilterName() {return (this.filterName);}public void setFilterName(String filterName) {this.filterName = filterName;} private String largeIcon = null;public String getLargeIcon() {return (this.largeIcon);}public void setLargeIcon(String largeIcon) {this.largeIcon = largeIcon;} private Map parameters = new HashMap();public Map getParameterMap() {return (this.parameters);}private String smallIcon = null;public String getSmallIcon() {return (this.smallIcon);}public void setSmallIcon(String smallIcon) {this.smallIcon = smallIcon;} public void addInitParameter(String name, String value) {parameters.put(name, value);}public String toString() {StringBuffer sb = new StringBuffer("FilterDef[");sb.append("filterName=");sb.append(this.filterName);sb.append(", filterClass=");sb.append(this.filterClass);sb.append("]");return (sb.toString());} }
【7】ApplicationFilterConfig類（org.apache.catalina.core.ApplicationFilterConfig-應(yīng)用過濾器配置類） 1）intro：ApplicationFilterConfig類實(shí)現(xiàn)了 javax.servlet.FilterConfig接口，該類用于管理web 應(yīng)用程序第1次啟動時(shí)創(chuàng)建的所有過濾器實(shí)例； 2）類簽名：final class ApplicationFilterConfig implements FilterConfig? 3）可以通過把一個(gè) org.apache.catalina.Context對象和 一個(gè) FilterDef對象傳遞給 ApplicationFilterConfig類的構(gòu)造函數(shù)來創(chuàng)建一個(gè) ApplicationFilterConfig對象：? public ApplicationFilterConfig(Context context, FilterDef filterDef)throws ClassCastException, ClassNotFoundException,IllegalAccessException, InstantiationException,ServletException {super();this.context = context;setFilterDef(filterDef);} 對以上代碼的分析（Analysis）： A1）Context對象表示一個(gè)web 應(yīng)用程序； A2）FilterDef對象表示一個(gè)過濾器的定義； 4）ApplicationFilterConfig.getFilter()方法：會返回一個(gè) javax.servlet.Filter對象，該方法負(fù)責(zé)載入并實(shí)例化一個(gè)過濾器類；? public String getFilterName() { // org.apache.catalina.core.ApplicationFilterConfig.getFilterName().return (filterDef.getFilterName()); }
【8】ApplicationFilterChain類（org.apache.catalina.core.ApplicationFilterChain） 1）intro：?ApplicationFilterChain類實(shí)現(xiàn)了 javax.servlet.FilterChain接口，StandardWrapperValve.invoke() 方法會創(chuàng)建 ApplicationFilterChain類的一個(gè)實(shí)例，并調(diào)用其 doFilter()方法； 2）Filter接口的doFilter()方法的簽名如下： public interface Filter { // javax.servlet.Filterpublic void init(FilterConfig filterConfig) throws ServletException; public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException; public void destroy(); }3）ApplicationFilterChain.doFilter()方法會將?ApplicationFilterChain 類自身作為第3個(gè)參數(shù)傳遞給過濾器的 doFilter()方法； public void doFilter(ServletRequest request, ServletResponse response) //org.apache.catalina.ApplicationFilterChain.doFileter().throws IOException, ServletException {if( System.getSecurityManager() != null ) {final ServletRequest req = request;final ServletResponse res = response;try {java.security.AccessController.doPrivileged(new java.security.PrivilegedExceptionAction(){public Object run() throws ServletException, IOException {internalDoFilter(req,res);return null;}});} catch( PrivilegedActionException pe) {Exception e = pe.getException();if (e instanceof ServletException)throw (ServletException) e;else if (e instanceof IOException)throw (IOException) e;else if (e instanceof RuntimeException)throw (RuntimeException) e;elsethrow new ServletException(e.getMessage(), e);}} else {internalDoFilter(request,response);}} 4）在Filter.doFilter()方法中， 可以通過顯示地調(diào)用 FileterChain.doFilter()方法來調(diào)用另一個(gè)過濾器。
對以上代碼的分析（Analysis）： A1）正如你所看到的，在doFilter()方法的最后一行會調(diào)用FilterChain.doFilter()方法； A2)如果某個(gè)過濾器時(shí)過濾器鏈中的最后一個(gè)過濾器，則會調(diào)用被請求的 servlet類的 service()方法。如果過濾器沒有調(diào)用chain.doFilter()方法，則不會調(diào)用后面的過濾器；
【9】應(yīng)用程序 0）servlet文件目錄
1）程序源代碼 public final class Bootstrap {public static void main(String[] args) {//invoke: http://localhost:8080/Modern or http://localhost:8080/PrimitiveSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new StandardWrapper();wrapper1.setName("Primitive");wrapper1.setServletClass("servlet.PrimitiveServlet"); // attention for servlet class，要與你的servlet目錄相對應(yīng)；Wrapper wrapper2 = new StandardWrapper();wrapper2.setName("Modern");wrapper2.setServletClass("servlet.ModernServlet"); // attention for servlet class，要與你的servlet目錄相對應(yīng)；Context context = new StandardContext();// StandardContext's start method adds a default mappercontext.setPath("/myApp");context.setDocBase("myApp");LifecycleListener listener = new SimpleContextConfig();((Lifecycle) context).addLifecycleListener(listener);context.addChild(wrapper1);context.addChild(wrapper2);// for simplicity, we don't add a valve, but you can add// valves to context or wrapper just as you did in Chapter 6Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");// add ContextConfig. This listener is important because it configures// StandardContext (sets configured to true), otherwise StandardContext// won't startconnector.setContainer(context);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) context).start();// make the application wait until we press a key.System.in.read();((Lifecycle) context).stop();}catch (Exception e) {e.printStackTrace();}} } 2）打印結(jié)果 E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common. jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/;lib/catalina.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot com.tomca t.chapter11.startup.Bootstrap HttpConnector Opening server socket on all host IP addresses HttpConnector[8080] Starting background thread WebappLoader[/myApp]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\_\myApp StandardManager[/myApp]: Seeding random number generator class java.security.SecureRandom StandardManager[/myApp]: Seeding of random number generator has been completed StandardManager[/myApp]: IOException while loading persisted sessions: java.io.EOFException // // 這是從文件中加載 session對象到內(nèi)存，由于沒有相關(guān)文件，所以加載失敗，拋出異常，但這不會影響我們訪問servlet，大家不要驚慌； java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter11.startup.Bootstrap.main(Bootstrap.java:55) StandardManager[/myApp]: Exception loading sessions from persistent storage java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter11.startup.Bootstrap.main(Bootstrap.java:55) ModernServlet -- init
總結(jié)
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