Servlet

標(biāo)簽 ： Java與Web

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Upload-上傳

隨著3.0版本的發(fā)布,文件上傳終于成為Servlet規(guī)范的一項內(nèi)置特性,不再依賴于像Commons FileUpload之類組件,因此在服務(wù)端進行文件上傳編程變得不費吹灰之力.

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客戶端

要上傳文件, 必須利用multipart/form-data設(shè)置HTML表單的enctype屬性,且method必須為POST:

<form action="simple_file_upload_servlet.do" method="POST" enctype="multipart/form-data"><table align="center" border="1" width="50%"><tr><td>Author:</td><td><input type="text" name="author"></td></tr><tr><td>Select file to Upload:</td><td><input type="file" name="file"></td></tr><tr><td><input type="submit" value="上傳"></td></tr></table> </form>

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服務(wù)端

服務(wù)端Servlet主要圍繞著@MultipartConfig注解和Part接口:

處理上傳文件的Servlet必須用@MultipartConfig注解標(biāo)注:

@MultipartConfig屬性描述

fileSizeThreshold	The size threshold after which the file will be written to disk
location	The directory location where files will be stored
maxFileSize	The maximum size allowed for uploaded files.
maxRequestSize	The maximum size allowed for multipart/form-data requests

在一個由多部件組成的請求中, 每一個表單域(包括非文件域), 都會被封裝成一個Part,HttpServletRequest中提供如下兩個方法獲取封裝好的Part:

HttpServletRequest描述

Part getPart(String name)	Gets the Part with the given name.
Collection<Part> getParts()	Gets all the Part components of this request, provided that it is of type multipart/form-data.

Part中提供了如下常用方法來獲取/操作上傳的文件/數(shù)據(jù):

Part描述

InputStream getInputStream()	Gets the content of this part as an InputStream
void write(String fileName)	A convenience method to write this uploaded item to disk.
String getSubmittedFileName()	Gets the file name specified by the client(需要有Tomcat 8.x 及以上版本支持)
long getSize()	Returns the size of this fille.
void delete()	Deletes the underlying storage for a file item, including deleting any associated temporary disk file.
String getName()	Gets the name of this part
String getContentType()	Gets the content type of this part.
Collection<String> getHeaderNames()	Gets the header names of this Part.
String getHeader(String name)	Returns the value of the specified mime header as a String.

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文件流解析

通過抓包獲取到客戶端上傳文件的數(shù)據(jù)格式:

------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh Content-Disposition: form-data; name="author"feiqing ------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh Content-Disposition: form-data; name="file"; filename="memcached.txt" Content-Type: text/plain------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh-- 可以看到:

A. 如果HTML表單輸入項為文本(<input type="text"/>),將只包含一個請求頭Content-Disposition.

B. 如果HTML表單輸入項為文件(<input type="file"/>), 則包含兩個頭:
Content-Disposition與Content-Type.

在Servlet中處理上傳文件時, 需要:

- 通過查看是否存在`Content-Type`標(biāo)頭, 檢驗一個Part是封裝的普通表單域,還是文件域. - 若有`Content-Type`存在, 但文件名為空, 則表示沒有選擇要上傳的文件. - 如果有文件存在, 則可以調(diào)用`write()`方法來寫入磁盤, 調(diào)用同時傳遞一個絕對路徑, 或是相對于`@MultipartConfig`注解的`location`屬性的相對路徑.

• SimpleFileUploadServlet

/*** @author jifang.* @since 2016/5/8 16:27.*/ @MultipartConfig @WebServlet(name = "SimpleFileUploadServlet", urlPatterns = "/simple_file_upload_servlet.do") public class SimpleFileUploadServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter writer = response.getWriter();Part file = request.getPart("file");if (!isFileValid(file)) {writer.print("<h1>請確認(rèn)上傳文件是否正確!");} else {String fileName = file.getSubmittedFileName();String saveDir = getServletContext().getRealPath("/WEB-INF/files/");mkdirs(saveDir);file.write(saveDir + fileName);writer.print("<h3>Uploaded file name: " + fileName);writer.print("<h3>Size: " + file.getSize());writer.print("<h3>Author: " + request.getParameter("author"));}}private void mkdirs(String saveDir) {File dir = new File(saveDir);if (!dir.exists()) {dir.mkdirs();}}private boolean isFileValid(Part file) {// 上傳的并非文件if (file.getContentType() == null) {return false;}// 沒有選擇任何文件else if (Strings.isNullOrEmpty(file.getSubmittedFileName())) {return false;}return true;} }

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優(yōu)化

• 善用WEB-INF
  存放在/WEB-INF/目錄下的資源無法在瀏覽器地址欄直接訪問, 利用這一特點可將某些受保護資源存放在WEB-INF目錄下, 禁止用戶直接訪問(如用戶上傳的可執(zhí)行文件,如JSP等),以防被惡意執(zhí)行, 造成服務(wù)器信息泄露等危險.

getServletContext().getRealPath("/WEB-INF/")

• 文件名亂碼
  當(dāng)文件名包含中文時,可能會出現(xiàn)亂碼,其解決方案與POST相同:

request.setCharacterEncoding("UTF-8");

• 避免文件同名
  如果上傳同名文件,會造成文件覆蓋.因此可以為每份文件生成一個唯一ID,然后連接原始文件名:

private String generateUUID() {return UUID.randomUUID().toString().replace("-", "_"); }

• 目錄打散
  如果一個目錄下存放的文件過多, 會導(dǎo)致文件檢索速度下降,因此需要將文件打散存放到不同目錄中, 在此我們采用Hash打散法(根據(jù)文件名生成Hash值, 取Hash值的前兩個字符作為二級目錄名), 將文件分布到一個二級目錄中:

private String generateTwoLevelDir(String destFileName) {String hash = Integer.toHexString(destFileName.hashCode());return String.format("%s/%s", hash.charAt(0), hash.charAt(1)); }

采用Hash打散的好處是:在根目錄下最多生成16個目錄,而每個子目錄下最多再生成16個子子目錄,即一共256個目錄,且分布較為均勻.

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示例-簡易存儲圖片服務(wù)器

需求: 提供上傳圖片功能, 為其生成外鏈, 并提供下載功能(見下)

• 客戶端

<html> <head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>IFS</title> </head> <body> <form action="ifs_upload.action" method="POST" enctype="multipart/form-data"><table align="center" border="1" width="50%"><tr><td>Select A Image to Upload:</td><td><input type="file" name="image"></td></tr><tr><td>&nbsp;</td><td><input type="submit" value="上傳"></td></tr></table> </form> </body> </html>

• 服務(wù)端

@MultipartConfig @WebServlet(name = "ImageFileUploadServlet", urlPatterns = "/ifs_upload.action") public class ImageFileUploadServlet extends HttpServlet {private Set<String> imageSuffix = new HashSet<>();private static final String SAVE_ROOT_DIR = "/images";{imageSuffix.add(".jpg");imageSuffix.add(".png");imageSuffix.add(".jpeg");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");PrintWriter writer = response.getWriter();Part image = request.getPart("image");String fileName = getFileName(image);if (isFileValid(image, fileName) && isImageValid(fileName)) {String destFileName = generateDestFileName(fileName);String twoLevelDir = generateTwoLevelDir(destFileName);// 保存文件String saveDir = String.format("%s/%s/", getServletContext().getRealPath(SAVE_ROOT_DIR), twoLevelDir);makeDirs(saveDir);image.write(saveDir + destFileName);// 生成外鏈String ip = request.getLocalAddr();int port = request.getLocalPort();String path = request.getContextPath();String urlPrefix = String.format("http://%s:%s%s", ip, port, path);String urlSuffix = String.format("%s/%s/%s", SAVE_ROOT_DIR, twoLevelDir, destFileName);String url = urlPrefix + urlSuffix;String result = String.format("<a href=%s>%s</a><hr/><a href=ifs_download.action?location=%s>下載</a>",url,url,saveDir + destFileName);writer.print(result);} else {writer.print("Error : Image Type Error");}}/*** 校驗文件表單域有效** @param file* @param fileName* @return*/private boolean isFileValid(Part file, String fileName) {// 上傳的并非文件if (file.getContentType() == null) {return false;}// 沒有選擇任何文件else if (Strings.isNullOrEmpty(fileName)) {return false;}return true;}/*** 校驗文件后綴有效** @param fileName* @return*/private boolean isImageValid(String fileName) {for (String suffix : imageSuffix) {if (fileName.endsWith(suffix)) {return true;}}return false;}/*** 加速圖片訪問速度, 生成兩級存放目錄** @param destFileName* @return*/private String generateTwoLevelDir(String destFileName) {String hash = Integer.toHexString(destFileName.hashCode());return String.format("%s/%s", hash.charAt(0), hash.charAt(1));}private String generateUUID() {return UUID.randomUUID().toString().replace("-", "_");}private String generateDestFileName(String fileName) {String destFileName = generateUUID();int index = fileName.lastIndexOf(".");if (index != -1) {destFileName += fileName.substring(index);}return destFileName;}private String getFileName(Part part) {String[] elements = part.getHeader("content-disposition").split(";");for (String element : elements) {if (element.trim().startsWith("filename")) {return element.substring(element.indexOf("=") + 1).trim().replace("\"", "");}}return null;}private void makeDirs(String saveDir) {File dir = new File(saveDir);if (!dir.exists()) {dir.mkdirs();}} }

由于getSubmittedFileName()方法需要有Tomcat 8.X以上版本的支持, 因此為了通用期間, 我們自己解析content-disposition請求頭, 獲取filename.

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Download-下載

文件下載是向客戶端響應(yīng)二進制數(shù)據(jù)(而非字符),瀏覽器不會直接顯示這些內(nèi)容,而是會彈出一個下載框, 提示下載信息.

為了將資源發(fā)送給瀏覽器, 需要在Servlet中完成以下工作:

• 使用Content-Type響應(yīng)頭來規(guī)定響應(yīng)體的MIME類型, 如image/pjpeg、application/octet-stream;
• 添加Content-Disposition響應(yīng)頭,賦值為attachment;filename=xxx.yyy, 設(shè)置文件名;
• 使用response.getOutputStream()給瀏覽器發(fā)送二進制數(shù)據(jù);

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文件名中文亂碼

當(dāng)文件名包含中文時(attachment;filename=文件名.后綴名),在下載框中會出現(xiàn)亂碼, 需要對文件名編碼后在發(fā)送, 但不同的瀏覽器接收的編碼方式不同:

* FireFox: Base64編碼* 其他大部分Browser: URL編碼

因此最好將其封裝成一個通用方法:

private String filenameEncoding(String filename, HttpServletRequest request) throws IOException {// 根據(jù)瀏覽器信息判斷if (request.getHeader("User-Agent").contains("Firefox")) {filename = String.format("=?utf-8?B?%s?=", BaseEncoding.base64().encode(filename.getBytes("UTF-8")));} else {filename = URLEncoder.encode(filename, "utf-8");}return filename; }

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示例-IFS下載功能

/*** @author jifang.* @since 2016/5/9 17:50.*/ @WebServlet(name = "ImageFileDownloadServlet", urlPatterns = "/ifs_download.action") public class ImageFileDownloadServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("application/octet-stream");String fileLocation = request.getParameter("location");String fileName = fileLocation.substring(fileLocation.lastIndexOf("/") + 1);response.setHeader("Content-Disposition", "attachment;filename=" + filenameEncoding(fileName, request));ByteStreams.copy(new FileInputStream(fileLocation), response.getOutputStream());}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);} }

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Async-異步處理

Servlet/Filter默認(rèn)會一直占用請求處理線程, 直到它完成任務(wù).如果任務(wù)耗時長久, 且并發(fā)用戶請求量大, Servlet容器將會遇到超出線程數(shù)的風(fēng)險.

Servlet 3.0 中新增了一項特性, 用來處理異步操作. 當(dāng)Servlet/Filter應(yīng)用程序中有一個/多個長時間運行的任務(wù)時, 你可以選擇將任務(wù)分配給一個新的線程, 從而將當(dāng)前請求處理線程返回到線程池中,釋放線程資源,準(zhǔn)備為下一個請求服務(wù).

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異步Servlet/Filter

• 異步支持
  @WebServlet/@WebFilter注解提供了新的asyncSupport屬性:

@WebFilter(asyncSupported = true) @WebServlet(asyncSupported = true)

同樣部署描述符中也添加了<async-supportted/>標(biāo)簽:

<servlet><servlet-name>HelloServlet</servlet-name><servlet-class>com.fq.web.servlet.HelloServlet</servlet-class><async-supported>true</async-supported> </servlet>

• Servlet/Filter
  支持異步處理的Servlet/Filter可以通過在ServletRequest中調(diào)用startAsync()方法來啟動新線程:

ServletRequest描述

AsyncContext startAsync()	Puts this request into asynchronous mode, and initializes its AsyncContext with the original (unwrapped) ServletRequest and ServletResponse objects.
AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse)	Puts this request into asynchronous mode, and initializes its AsyncContext with the given request and response objects.

注意:
1. 只能將原始的ServletRequest/ServletResponse或其包裝器(Wrapper/Decorator,詳見Servlet - Listener、Filter、Decorator)傳遞給第二個startAsync()方法.
2. 重復(fù)調(diào)用startAsync()方法會返回相同的AsyncContext實例, 如果在不支持異步處理的Servlet/Filter中調(diào)用, 會拋出java.lang.IllegalStateException異常.
3. AsyncContext的start()方法不會造成方法阻塞.

這兩個方法都返回AsyncContext實例, AsyncContext中提供了如下常用方法:

AsyncContext描述

void start(Runnable run)	Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable.
void dispatch(String path)	Dispatches the request and response objects of this AsyncContext to the given path.
void dispatch(ServletContext context, String path)	Dispatches the request and response objects of this AsyncContext to the given path scoped to the given context.
void addListener(AsyncListener listener)	Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods.
ServletRequest getRequest()	Gets the request that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse).
ServletResponse getResponse()	Gets the response that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse).
boolean hasOriginalRequestAndResponse()	Checks if this AsyncContext was initialized with the original or application-wrapped request and response objects.
void setTimeout(long timeout)	Sets the timeout (in milliseconds) for this AsyncContext.

在異步Servlet/Filter中需要完成以下工作, 才能真正達到異步的目的:

• 調(diào)用AsyncContext的start()方法, 傳遞一個執(zhí)行長時間任務(wù)的Runnable;
• 任務(wù)完成時, 在Runnable內(nèi)調(diào)用AsyncContext的complete()方法或dispatch()方法

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示例-改造文件上傳

在前面的圖片存儲服務(wù)器中, 如果上傳圖片過大, 可能會耗時長久,為了提升服務(wù)器性能, 可將其改造為異步上傳(其改造成本較小):

@Override protected void doPost(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {final AsyncContext asyncContext = request.startAsync();asyncContext.start(new Runnable() {@Overridepublic void run() {try {request.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");PrintWriter writer = response.getWriter();Part image = request.getPart("image");final String fileName = getFileName(image);if (isFileValid(image, fileName) && isImageValid(fileName)) {String destFileName = generateDestFileName(fileName);String twoLevelDir = generateTwoLevelDir(destFileName);// 保存文件String saveDir = String.format("%s/%s/", getServletContext().getRealPath(SAVE_ROOT_DIR), twoLevelDir);makeDirs(saveDir);image.write(saveDir + destFileName);// 生成外鏈String ip = request.getLocalAddr();int port = request.getLocalPort();String path = request.getContextPath();String urlPrefix = String.format("http://%s:%s%s", ip, port, path);String urlSuffix = String.format("%s/%s/%s", SAVE_ROOT_DIR, twoLevelDir, destFileName);String url = urlPrefix + urlSuffix;String result = String.format("<a href=%s>%s</a><hr/><a href=ifs_download.action?location=%s>下載</a>",url,url,saveDir + destFileName);writer.print(result);} else {writer.print("Error : Image Type Error");}asyncContext.complete();} catch (ServletException | IOException e) {LOGGER.error("error: ", e);}}}); }

注意: Servlet異步支持只適用于長時間運行,且想讓用戶知道執(zhí)行結(jié)果的任務(wù). 如果只有長時間, 但用戶不需要知道處理結(jié)果,那么只需提供一個Runnable提交給Executor, 并立即返回即可.

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AsyncListener

Servlet 3.0 還新增了一個AsyncListener接口, 以便通知用戶在異步處理期間發(fā)生的事件, 該接口會在異步操作的啟動/完成/失敗/超時情況下調(diào)用其對應(yīng)方法:

• ImageUploadListener

/*** @author jifang.* @since 2016/5/10 17:33.*/ public class ImageUploadListener implements AsyncListener {@Overridepublic void onComplete(AsyncEvent event) throws IOException {System.out.println("onComplete...");}@Overridepublic void onTimeout(AsyncEvent event) throws IOException {System.out.println("onTimeout...");}@Overridepublic void onError(AsyncEvent event) throws IOException {System.out.println("onError...");}@Overridepublic void onStartAsync(AsyncEvent event) throws IOException {System.out.println("onStartAsync...");} }

與其他監(jiān)聽器不同, 他沒有@WebListener標(biāo)注AsyncListener的實現(xiàn), 因此必須對有興趣收到通知的每個AsyncContext都手動注冊一個AsyncListener:

asyncContext.addListener(new ImageUploadListener());

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動態(tài)注冊

動態(tài)注冊是Servlet 3.0新特性,它不需要重新加載應(yīng)用便可安裝新的Web對象(Servlet/Filter/Listener等).

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API支持

為了使動態(tài)注冊成為可能, ServletContext接口添加了如下方法用于 創(chuàng)建/添加 Web對象:

ServletContext描述

Create
<T extends Servlet> T createServlet(Class<T> clazz)	Instantiates the given Servlet class.
<T extends Filter> T createFilter(Class<T> clazz)	Instantiates the given Filter class.
<T extends EventListener> T createListener(Class<T> clazz)	Instantiates the given EventListener class.
Add
ServletRegistration.Dynamic addServlet(String servletName, Servlet servlet)	Registers the given servlet instance with this ServletContext under the given servletName.
FilterRegistration.Dynamic addFilter(String filterName, Filter filter)	Registers the given filter instance with this ServletContext under the given filterName.
<T extends EventListener> void addListener(T t)	Adds the given listener to this ServletContext.
Create & And
ServletRegistration.Dynamic addServlet(String servletName, Class<? extends Servlet> servletClass)	Adds the servlet with the given name and class type to this servlet context.
ServletRegistration.Dynamic addServlet(String servletName, String className)	Adds the servlet with the given name and class name to this servlet context.
FilterRegistration.Dynamic addFilter(String filterName, Class<? extends Filter> filterClass)	Adds the filter with the given name and class type to this servlet context.
FilterRegistration.Dynamic addFilter(String filterName, String className)	Adds the filter with the given name and class name to this servlet context.
void addListener(Class<? extends EventListener> listenerClass)	Adds a listener of the given class type to this ServletContext.
void addListener(String className)	Adds the listener with the given class name to this ServletContext.

其中addServlet()/addFilter()方法的返回值是ServletRegistration.Dynamic/FilterRegistration.Dynamic,他們都是Registration.Dynamic的子接口,用于動態(tài)配置Servlet/Filter實例.

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示例-DynamicServlet

動態(tài)注冊DynamicServlet, 注意: 并未使用web.xml或@WebServlet靜態(tài)注冊DynamicServlet實例, 而是用DynRegListener在服務(wù)器啟動時動態(tài)注冊.

• DynamicServlet

/*** @author jifang.* @since 2016/5/13 16:41.*/ public class DynamicServlet extends HttpServlet {private String dynamicName;@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.getWriter().print("<h1>DynamicServlet, MyDynamicName: " + getDynamicName() + "</h1>");}public String getDynamicName() {return dynamicName;}public void setDynamicName(String dynamicName) {this.dynamicName = dynamicName;} }

• DynRegListener

@WebListener public class DynRegListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent sce) {ServletContext context = sce.getServletContext();DynamicServlet servlet;try {servlet = context.createServlet(DynamicServlet.class);} catch (ServletException e) {servlet = null;}if (servlet != null) {servlet.setDynamicName("Hello fQ Servlet");ServletRegistration.Dynamic dynamic = context.addServlet("dynamic_servlet", servlet);dynamic.addMapping("/dynamic_servlet.do");}}@Overridepublic void contextDestroyed(ServletContextEvent sce) {} }

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容器初始化

在使用類似SpringMVC這樣的MVC框架時,需要首先注冊DispatcherServlet到web.xml以完成URL的轉(zhuǎn)發(fā)映射:

<!-- 配置SpringMVC --> <servlet><servlet-name>mvc</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring/mvc-servlet.xml</param-value></init-param><load-on-startup>1</load-on-startup> </servlet> <servlet-mapping><servlet-name>mvc</servlet-name><url-pattern>*.do</url-pattern> </servlet-mapping>

在Servlet 3.0中,通過Servlet容器初始化,可以自動完成Web對象的首次注冊,因此可以省略這個步驟.

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API支持

容器初始化的核心是javax.servlet.ServletContainerInitializer接口,他只包含一個方法:

ServletContainerInitializer描述

void onStartup(Set<Class<?>> c, ServletContext ctx)	Notifies this ServletContainerInitializer of the startup of the application represented by the given ServletContext.

在執(zhí)行任何ServletContext監(jiān)聽器之前, 由Servlet容器自動調(diào)用onStartup()方法.

注意: 任何實現(xiàn)了ServletContainerInitializer的類必須使用@HandlesTypes注解標(biāo)注, 以聲明該初始化程序可以處理這些類型的類.

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實例-SpringMVC初始化

利用Servlet容器初始化, SpringMVC可實現(xiàn)容器的零配置注冊.

• SpringServletContainerInitializer

@HandlesTypes(WebApplicationInitializer.class) public class SpringServletContainerInitializer implements ServletContainerInitializer {@Overridepublic void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)throws ServletException {List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();if (webAppInitializerClasses != null) {for (Class<?> waiClass : webAppInitializerClasses) {// Be defensive: Some servlet containers provide us with invalid classes,// no matter what @HandlesTypes says...if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&WebApplicationInitializer.class.isAssignableFrom(waiClass)) {try {initializers.add((WebApplicationInitializer) waiClass.newInstance());}catch (Throwable ex) {throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);}}}}if (initializers.isEmpty()) {servletContext.log("No Spring WebApplicationInitializer types detected on classpath");return;}AnnotationAwareOrderComparator.sort(initializers);servletContext.log("Spring WebApplicationInitializers detected on classpath: " + initializers);for (WebApplicationInitializer initializer : initializers) {initializer.onStartup(servletContext);}}}

SpringMVC為ServletContainerInitializer提供了實現(xiàn)類SpringServletContainerInitializer通過查看源代碼可以知道,我們只需提供WebApplicationInitializer的實現(xiàn)類到classpath下, 即可完成對所需Servlet/Filter/Listener的注冊.

public interface WebApplicationInitializer {void onStartup(ServletContext servletContext) throws ServletException; }

詳細可參考springmvc基于java config的實現(xiàn)

• javax.servlet.ServletContainerInitializer

org.springframework.web.SpringServletContainerInitializer

元數(shù)據(jù)文件javax.servlet.ServletContainerInitializer只有一行內(nèi)容(即實現(xiàn)了ServletContainerInitializer類的全限定名),該文本文件必須放在jar包的META-INF/services目錄下.

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轉(zhuǎn)載于:https://www.cnblogs.com/itrena/p/5926895.html

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