【0】README

0.1）本文部分文字轉自　“深入剖析Tomcat”，旨在學習 ?一個簡單的servlet容器 ?的基礎知識；

0.2）for complete source code, please visit?https://github.com/pacosonTang/HowTomcatWorks/tree/master/chapter2

0.3）溫馨建議：建議閱讀本文之前，已閱讀過 tomcat(1)的系列文章，因為它們是環(huán)環(huán)相扣的；

【1】javax.servlet.Servlet接口

1）intro Servlet：Servlet編程需要使用到 javax.servlet 和 javax.servlet.http 兩個包下的接口和類。在所有的類和接口中， javax.servlet.servlet 接口是最為重要的。所有的servlet 程序都必須實現該接口或繼承自實現了該接口的類； 2）Servlet接口中聲明了5個方法： init， service， destroy， getServletConfig， getServletInfo 方法；（干貨——Servlet接口中聲明了5個方法） 2.0）init， service， destroy方法是與 servlet的生命周期相關的方法； 2.1）init方法：當實例化某個servlet類后；servlet容器會調用其 init() 方法進行初始化，servlet只調用該方法一次；且servlet 程序員可以覆蓋此方法，在其中編寫僅需要執(zhí)行一次的初始化代碼； 2.2）service方法：當一個servlet客戶端請求到達后，servlet容器就調用相應的servlet的service方法，并將 servletRequest 和 servletResponse 對象作為參數傳入； 2.3）destroy方法：當servlet容器關閉或servlet容器要釋放內存時，才會將 servlet實例移除，而且只有當servlet實例的service方法中的所有線程都退出或執(zhí)行超時后，才會調用 destroy方法； 3）看個荔枝： public class PrimitiveServlet implements Servlet {public void init(ServletConfig config) throws ServletException {System.out.println("init");}public void service(ServletRequest request, ServletResponse response)throws ServletException, IOException {System.out.println("from service");PrintWriter out = response.getWriter();out.println("Hello. Roses are red.");out.print("Violets are blue.");}public void destroy() {System.out.println("destroy");}public String getServletInfo() {return null;}public ServletConfig getServletConfig() {return null;} }
【2】應用程序1 1）一個功能齊全的 servlet容器有以下幾件事情要做（things）：（干貨——servlet容器需要做的事情） t1）當第一次調用某個 servlet 時，要載入該 servlet類，并調用其 init() 方法；（干貨——servlet僅調用該方法一次） t2）針對每個request請求， 創(chuàng)建一個 javax.servlet.ServletRequest 實例 和 一個 javax.servlet.ServletResponse 實例； t3）調用該 servlet 的 service() 方法，將 servletRequest對象和 servletResponse對象作為參數傳入；（參見上述PrimitiveServlet的定義） t4）當關閉該servlet類時，調用其 destroy() 方法，并卸載該servlet類； 2）servlet容器的實現源碼和訪問結果 2.1）printing results
2.2）soruce code at a glance // HttpServer1 類 既可以對靜態(tài)資源請求，也可以對servlet資源請求 public class HttpServer1 { private static final String SHUTDOWN_COMMAND = "/SHUTDOWN"; private boolean shutdown = false;public static void main(String[] args) {HttpServer1 server = new HttpServer1();server.await();}public void await() {ServerSocket serverSocket = null;int port = 8080;try {serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));}catch (IOException e) {e.printStackTrace();System.exit(1);}// Loop waiting for a requestwhile (!shutdown) {Socket socket = null;InputStream input = null;OutputStream output = null;try {socket = serverSocket.accept();input = socket.getInputStream();output = socket.getOutputStream();// create Request object and parseRequest request = new Request(input);request.parse();// create Response objectResponse response = new Response(output);response.setRequest(request);// check if this is a request for a servlet or a static resource// a request for a servlet begins with "/servlet/"if (request.getUri().startsWith("/servlet/")) { // 若HTTP請求的是servlet(以servlet打頭)ServletProcessor1 processor = new ServletProcessor1();processor.process(request, response);} // 若http請求的是靜態(tài)資源else {StaticResourceProcessor processor = new StaticResourceProcessor();processor.process(request, response);}// Close the socketsocket.close();//check if the previous URI is a shutdown commandshutdown = request.getUri().equals(SHUTDOWN_COMMAND);}catch (Exception e) {e.printStackTrace();System.exit(1);}}} } package com.tomcat.chapter2;import java.io.File;public class Constants { // 常數類，封裝了 WEB_ROOT 常量public static final String WEB_ROOT =System.getProperty("user.dir") + File.separator + "webroot"; }// Request: HTTP請求對象，其parse方法用于讀取HTTP請求頭；其parseUri方法用于解析client 請求的 uri public class Request implements ServletRequest {private InputStream input;private String uri;public Request(InputStream input) {this.input = input;}public String getUri() {return uri;}private String parseUri(String requestString) {int index1, index2;index1 = requestString.indexOf(' ');if (index1 != -1) {index2 = requestString.indexOf(' ', index1 + 1);if (index2 > index1)return requestString.substring(index1 + 1, index2);}return null;}public void parse() {// Read a set of characters from the socketStringBuffer request = new StringBuffer(2048);int i;byte[] buffer = new byte[2048];try {i = input.read(buffer);}catch (IOException e) {e.printStackTrace();i = -1;}for (int j=0; j<i; j++) {request.append((char) buffer[j]);}System.out.print(request.toString());uri = parseUri(request.toString());}//...... some barren functions// Response：<span style="color: rgb(85, 85, 85); font-family: 宋體;">HTTP響應對象，其sendStaticResource方法 讀取request解析出的uri對應的資源文件，并發(fā)送該文件數據到client端； public class Response implements ServletResponse {private static final int BUFFER_SIZE = 1024;Request request;OutputStream output;PrintWriter writer;public Response(OutputStream output) {this.output = output;}public void setRequest(Request request) {this.request = request;}/* This method is used to serve a static page */public void sendStaticResource() throws IOException {byte[] bytes = new byte[BUFFER_SIZE];FileInputStream fis = null;try {/* request.getUri has been replaced by request.getRequestURI */File file = new File(Constants.WEB_ROOT, request.getUri());fis = new FileInputStream(file);/*HTTP Response = Status-Line*(( general-header | response-header | entity-header ) CRLF)CRLF[ message-body ]Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF*/int ch = fis.read(bytes, 0, BUFFER_SIZE);while (ch!=-1) {output.write(bytes, 0, ch);ch = fis.read(bytes, 0, BUFFER_SIZE);}}catch (FileNotFoundException e) {String errorMessage = "HTTP/1.1 404 File Not Found\r\n" +"Content-Type: text/html\r\n" +"Content-Length: 23\r\n" +"\r\n" +"<h1>File Not Found</h1>";output.write(errorMessage.getBytes());}finally {if (fis!=null)fis.close();}}/** implementation of ServletResponse */public PrintWriter getWriter() throws IOException {// autoflush is true, println() will flush,// but print() will not.writer = new PrintWriter(output, true);return writer;}// （servlet 處理器）用于處理對servlet 資源的HTTP 請求（干貨代碼，特別是里面的類加載器） public class ServletProcessor1 {public void process(Request request, Response response) {String uri = request.getUri();String servletName = uri.substring(uri.lastIndexOf("/") + 1);URLClassLoader loader = null; // 類載入器try {// create a URLClassLoader, 創(chuàng)建類載入器（類加載器是干貨代碼 ）URL[] urls = new URL[1];URLStreamHandler streamHandler = null;File classPath = new File(Constants.WEB_ROOT);// the forming of repository is taken from the createClassLoader method in// org.apache.catalina.startup.ClassLoaderFactoryString repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;// file:E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot\// the code for forming the URL is taken from the addRepository method in// org.apache.catalina.loader.StandardClassLoader class.urls[0] = new URL(null, repository, streamHandler);// urls[0] = file:E:/bench-cluster/cloud-data-preprocess/HowTomcatWorks/webroot/loader = new URLClassLoader(urls);}catch (IOException e) {System.out.println(e.toString() );}Class myClass = null;try {myClass = loader.loadClass("servlet."+servletName); // 載入 servlet類}catch (ClassNotFoundException e) {System.out.println(e.toString());}Servlet servlet = null;try {servlet = (Servlet) myClass.newInstance(); // 會創(chuàng)建已載入的servlet類的一個實例servlet.service((ServletRequest) request, (ServletResponse) response);}catch (Exception e) {System.out.println(e.toString());}catch (Throwable e) {System.out.println(e.toString());}} }public class StaticResourceProcessor {public void process(Request request, Response response) {try {response.sendStaticResource(); // 直接調用response的 sendStaticResource 方法.....}catch (IOException e) {e.printStackTrace();}} }

補充）本文總結了上述應用程序的調用流程圖

【3】應用程序2 1）problem：ServletProcessor1 中必須將Request 轉型為 javax.servlet.ServletRequest，將Response 轉型為 javax.servlet.ServletResponse 實例，將它們作為參數傳遞給 service方法； 1.1）這是不安全的做法： 一旦我們有了Request 實例后，我們就可以調用其parse方法，而有了Response實例后，我們就可以調用其 sendStaticResource方法。不能將parse() 和 sendStaticResource() 設置為私有方法，因為它們會被其他類調用，但這兩個方法在servlet中不應該是可用的； 2）solution：使用外觀類（Facade）來解決 2.1）構建外觀類 RequestFacade 和 ResponseFacade：分別實現 ServletRequest 和 ServletResponse ，然后在其構造函數中指定Request 和 Response對象（private私有訪問權限） ，外觀類中的實現方法均調用 Request 或 Response對象的相應方法； 3）Conclusion：引入外觀類的目的是， 不向外界提供訪問到Request 和 Response 的接口；（干貨——引入外觀類的目的是， 不向外界提供訪問到Request 和 Response 的接口） 4）源代碼實現和打印結果 4.1）打印結果同 HttpServer1，故 omit it； 4.2）源代碼實現（我這里給給出外觀類代碼，其他和HttpServer1 中的類似） public class HttpServer2 {// shutdown commandprivate static final String SHUTDOWN_COMMAND = "/SHUTDOWN";// the shutdown command receivedprivate boolean shutdown = false;public static void main(String[] args) {HttpServer2 server = new HttpServer2();server.await();}public void await() {ServerSocket serverSocket = null;int port = 8080;try {serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));}catch (IOException e) {e.printStackTrace();System.exit(1);}// Loop waiting for a requestwhile (!shutdown) {Socket socket = null;InputStream input = null;OutputStream output = null;try {socket = serverSocket.accept();input = socket.getInputStream();output = socket.getOutputStream();// create Request object and parseRequest request = new Request(input);request.parse();// create Response objectResponse response = new Response(output);response.setRequest(request);//check if this is a request for a servlet or a static resource//a request for a servlet begins with "/servlet/"if (request.getUri().startsWith("/servlet/")) {ServletProcessor2 processor = new ServletProcessor2();processor.process(request, response);}else {StaticResourceProcessor processor = new StaticResourceProcessor();processor.process(request, response);}// Close the socketsocket.close();//check if the previous URI is a shutdown commandshutdown = request.getUri().equals(SHUTDOWN_COMMAND);}catch (Exception e) {e.printStackTrace();System.exit(1);}}} }
public class RequestFacade implements ServletRequest {private ServletRequest request = null;public RequestFacade(Request request) {this.request = request;}/* implementation of the ServletRequest*/public Object getAttribute(String attribute) {return request.getAttribute(attribute);}public Enumeration getAttributeNames() {return request.getAttributeNames();}public String getRealPath(String path) {return request.getRealPath(path);}public RequestDispatcher getRequestDispatcher(String path) {return request.getRequestDispatcher(path);}public boolean isSecure() {return request.isSecure();}public String getCharacterEncoding() {return request.getCharacterEncoding();}public int getContentLength() {return request.getContentLength();}public String getContentType() {return request.getContentType();}public ServletInputStream getInputStream() throws IOException {return request.getInputStream();}public Locale getLocale() {return request.getLocale();}public Enumeration getLocales() {return request.getLocales();}public String getParameter(String name) {return request.getParameter(name);}public Map getParameterMap() {return request.getParameterMap();}public Enumeration getParameterNames() {return request.getParameterNames();}public String[] getParameterValues(String parameter) {return request.getParameterValues(parameter);}public String getProtocol() {return request.getProtocol();}public BufferedReader getReader() throws IOException {return request.getReader();}public String getRemoteAddr() {return request.getRemoteAddr();}public String getRemoteHost() {return request.getRemoteHost();}public String getScheme() {return request.getScheme();}public String getServerName() {return request.getServerName();}public int getServerPort() {return request.getServerPort();}public void removeAttribute(String attribute) {request.removeAttribute(attribute);}public void setAttribute(String key, Object value) {request.setAttribute(key, value);}public void setCharacterEncoding(String encoding)throws UnsupportedEncodingException {request.setCharacterEncoding(encoding);}}public class ResponseFacade implements ServletResponse {private ServletResponse response;public ResponseFacade(Response response) {this.response = response;}public void flushBuffer() throws IOException {response.flushBuffer();}public int getBufferSize() {return response.getBufferSize();}public String getCharacterEncoding() {return response.getCharacterEncoding();}public Locale getLocale() {return response.getLocale();}public ServletOutputStream getOutputStream() throws IOException {return response.getOutputStream();}public PrintWriter getWriter() throws IOException {return response.getWriter();}public boolean isCommitted() {return response.isCommitted();}public void reset() {response.reset();}public void resetBuffer() {response.resetBuffer();}public void setBufferSize(int size) {response.setBufferSize(size);}public void setContentLength(int length) {response.setContentLength(length);}public void setContentType(String type) {response.setContentType(type);}public void setLocale(Locale locale) {response.setLocale(locale);}}public class ServletProcessor2 {public void process(Request request, Response response) {String uri = request.getUri();String servletName = uri.substring(uri.lastIndexOf("/") + 1);URLClassLoader loader = null;try {URL[] urls = new URL[1];URLStreamHandler streamHandler = null;File classPath = new File(Constants.WEB_ROOT);String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;urls[0] = new URL(null, repository, streamHandler);loader = new URLClassLoader(urls);}catch (IOException e) {System.out.println(e.toString() );}Class myClass = null;try {myClass = loader.loadClass("servlet." + servletName);}catch (ClassNotFoundException e) {System.out.println(e.toString());}Servlet servlet = null;RequestFacade requestFacade = new RequestFacade(request); // attend this lineResponseFacade responseFacade = new ResponseFacade(response); <span style="font-family: 宋體;">// attend this line</span>try {servlet = (Servlet) myClass.newInstance();servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade); // and this line}catch (Exception e) {System.out.println(e.toString());}catch (Throwable e) {System.out.println(e.toString());}} }

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