Servlet3.0的新特性

时间：2023-03-08 16:04:18
注意：Servlet3.0的项目一定要使用Tomcat7.0才能看到效果！！

1、新增标注支持

    在Servlet3.0的部署描述文件web.xml的顶层标签<web-app>中有一个metadata-complete属性，如果把该属性的值设置为true，则容器在部署时只依赖于web.xml部署文件中的配置，会忽略所以的标注（同时也会跳过web-fragment.xml的扫描，即禁用可插性支持）；如果把该属性的值设置为false或者不配置该属性，则表示启用标注支持和可插性支持。
    1）WebServlet标注
    @WebServlet用于将一个类声明为Servlet，该标注将会在部署时被容器处理，容器将根据具体的属性配置将相应的类部署为Servlet。
    Servlet3.0的新特性
    2）WebInitParam标注
    @WebInitParam标注通常不单独使用，而是配合@WebServlet或者@WebFilter使用。它的作业是为Servlet或者过滤器指定初始化参数，这等价于web.xml中<servlet>和<filter>的<init-param>子标签
属性名 类型 是否可选 描述
name String 否 指定参数的名字，等价于<param-name>
value String 否 指定参数的值，等价于<param-value>
description String 是 指定参数的描述，等价于<description>
创建一个Servlet3Annotation类：
package com.yyq.servlet3.annotation;

import javax.servlet.ServletConfig;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebInitParam;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;

/**

 * Created by gao on 16-4-14.

 */

@WebServlet(name = "servlet3annotation", urlPatterns = {"/servlet3"},

        description = "servletinfo", displayName = "abc", asyncSupported = true, loadOnStartup = -1,

        initParams = {@WebInitParam(name = "username", value = "YangYuqin")})

public class Servlet3Annotation extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //获取ServletConfig的实例

        ServletConfig config = this.getServletConfig();

        //获取指定参数名称的值

        String name = config.getInitParameter("username");

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        out.println("<html>");

        out.println("<head><title>Servlet3应用实例</title></head>");

        out.println("<body>");

        out.print("获取InitParamServlet的初始化参数\"username\"的字符串值：" + name);

        out.println("</body>");

        out.println("</html>");

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

启动Tomcat，输入：http://localhost:8080/servlet3

Servlet3.0的新特性
    3）WebFilter标注
    @WebFilter用于将一个类声明为过滤器，该标注将会在部署时被容器处理。以下属性均为可选属性，但是value、urlPatterns、servletNames三者必需至少包含一个，且value和urlPattern不能共存，如果同时指定，通常忽略value的取值。
属性名 类型 描述
filterName String 指定过滤器的name属性，等价于<filter-name>
value String[] 该属性等价于urlPatterns属性，两个属性不能同时使用
urlPatterns String[] 指定一组Servlet的URL匹配模式，等价于<url-pattern>标签
servletNames String[] @WebServlet中的name属性的取值，或者是web.xml中<servlet-name>的取值
initParams WebInitParam[] 指定一组Servlet初始化参数，等价于<init-param>标签
dispatcherTypes DispatcherType 指定过滤器的转发模式。具体取值包括：ASYNC、ERROR、FORWARD、INCLUDE、REQUEST
asyncSupported boolean 声明过滤器是否支持异步操作模式，等价于<async-supported>标签
description String 该Servlet的描述信息，等价于<description>标签
displayName String 该Servlet的显示名，通常配合工具使用，等价于<display-name>标签 
package com.yyq.servlet3.filter;

import javax.servlet.*;

import javax.servlet.annotation.WebFilter;

import javax.servlet.annotation.WebInitParam;

import java.io.IOException;

/**

 * Created by gao on 16-4-14.

 */

@WebFilter(servletNames = {"servlet3filterannotation"}, filterName = "characterFilter",

        initParams = {@WebInitParam(name = "encoding", value = "UTF-8")})

public class Servlet3FilterAnnotation implements Filter {

    private FilterConfig filterConfig = null;

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;

    }

    @Override

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        //获取此Filter的初始参数的值

        String encoding = filterConfig.getInitParameter("encoding");

        System.out.println(encoding);

        //设置请求数据的编码方式

        servletRequest.setCharacterEncoding(encoding);

        //把请求和响应对象传给过滤链中的下一个要调用的过滤器或Servlet

        filterChain.doFilter(servletRequest,servletResponse);

    }

    @Override

    public void destroy() {

        //空

    }

}

　　4）WebListener标注

    该标注用于将类声明为监听器。
属性名 类型 是否可选 描述
value String 是 该监听器的描述信息
监听类：
package com.yyq.servlet3.listener;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSessionAttributeListener;

import javax.servlet.http.HttpSessionBindingEvent;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

import java.util.LinkedList;

import java.util.List;

/**

 * Created by gao on 16-4-14.

 */

@WebListener("This is the Listener")

public class Servlet3Listener implements ServletContextListener, HttpSessionAttributeListener, HttpSessionListener {

    private ServletContext application = null;

    //往会话中添加属性时回调的方法

    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {

        //取得用户名列表

        List<String> online = (List<String>) this.application.getAttribute("online");

        if ("username".equals(httpSessionBindingEvent.getName())) {

            //将当前用户名添加到列表中

            online.add((String) httpSessionBindingEvent.getValue());

        }

        //将添加后的列表重新设置到application属性中

        this.application.setAttribute("online", online);

    }

    //以下方法用空实现

    @Override

    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {

    }

    @Override

    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

    }

    @Override

    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

    }

    @Override

    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }

    //应用上下文初始化会回调的方法

    @Override

    public void contextInitialized(ServletContextEvent servletContextEvent) {

        //初始化一个application对象

        this.application = servletContextEvent.getServletContext();

        //设置一个列表属性，用于保存在线用户名

        this.application.setAttribute("online",new LinkedList<String>());

    }

    //会话销毁时会回调的方法

    @Override

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

        //取得用户名列表

        List<String> online = (List<String>) this.application.getAttribute("online");

        //取得当前用户名

        String username = (String) httpSessionEvent.getSession().getAttribute("username");

        //将此用户名从列表中删除

        online.remove(username);

        //将删除后的列表重新设置到application属性中

        this.application.setAttribute("online", online);

    }

}

登录Servlet类：

package com.yyq.servlet3.listener;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.List;

/**

 * Created by gao on 16-4-14.

 */

@WebServlet(name = "servlet3login",urlPatterns = {"/login"})

public class Servlet3Login extends HttpServlet {

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //设置响应内容类型

        req.setCharacterEncoding("utf-8");

        //获取请求参数中的用户名

        String username = req.getParameter("username");

        //往Session中添加属性

        //会触发HttpSessionAttributeListener中的attributeAdded方法

        if (username != null && !username.equals("")) {

            req.getSession().setAttribute("username", username);

        }

        //从应用上下文中获取在线用户名列表

        List<String> online = (List<String>) getServletContext().getAttribute("online");

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        out.println("<html>");

        out.println("<head><title>用户列表</title></head>");

        out.println("<body>");

        out.println("当前用户是：" + username);

        out.println("<hr/><h3>在线用户列表</h3>>");

        int size = ((online == null) ? 0 : online.size());

        for (int i = 0; i < size; i++) {

            if (i > 0) {

                out.println("<br />");

            }

            out.println(i + 1 + "." + online.get(i));

        }

        //注意：要对连接URL进行自动重写处理

        out.println("<hr/><a href=\"" + resp.encodeURL("logout") + "\">注销</a>");

        out.println("</body>");

        out.println("</html>");

        out.flush();

        out.close();

    }

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req, resp);

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

注销Servlet类：

package com.yyq.servlet3.listener;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.List;

/**

 * Created by gao on 16-4-14.

 */

@WebServlet(name = "servlet3logout", urlPatterns = {"/logout"})

public class Servlet3Logout extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //设置响应内容类型

        req.setCharacterEncoding("utf-8");

        //销毁会话，会触发SessionLinstener中的sessionDestroyed方法

        req.getSession().invalidate();

        //从应用上下文中获取在线用户名列表

        List<String> online = (List<String>)getServletContext().getAttribute("online");

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        out.println("<html>");

        out.println("<head><title>用户列表</title></head>");

        out.println("<body>");

        out.print("<h3>在线用户列表</h3>");

        int size = ((online == null) ? 0 : online.size());

        for (int i = 0; i < size; i++) {

            if (i > 0) {

                out.println("<br />");

            }

            out.println(i + 1 + "." + online.get(i));

        }

        out.println("<hr><a href=\"index.jsp\">主页</hr>");

        out.println("</body>");

        out.println("</html>");

        out.flush();

        out.close();

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

登录页面：index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>

<head>

    <title></title>

</head>

<body>

<form action="login" method="post">

    用户名：<input type="text" name="username">

    <input type="submit" value="登录">

    <br />

    <br />

</form>

</body>

</html>
    5）MultipartConfig标注
    该标注主要是为了辅助Servlet3.0中HttpServletRequest提供的对上传文件的支持。该标注标注在Servlet上，表示该Servlet希望处理的请求的MIME类型是multipart/form-data。
属性名 类型 是否可选 描述
fileSizeThreshold int 是 当数据量大于该值时，内容将被写入文件
location String 是 存放生成的文件地址
maxFileSize long 是 允许上传的文件最大值。默认值为-1，表示没有限制
maxRequestSize long 是 针对该multipart/form-data请求的最大数量，默认值为-1，表示没有限制

文件上传页面upload.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" pageEncoding="UTF-8" %>

<%

    String path = request.getContextPath();

    String basePath = request.getScheme() + "://" + request.getServerName() + ":"

            + request.getServerPort() + path + "/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

    <title>Servlet3.0 上传文件</title>

</head>

<body>

<form action="uploadfile" method="post" enctype="multipart/form-data">

    <table>

        <tr>

            <td>

                选择文件：

            </td>

            <td>

                <input type="file" name="file"/>

            </td>

        </tr>

        <tr>

            <td>描述:

            </td>

            <td>

                <input type="text" name="description"/>

            </td>

        </tr>

        <tr>

            <td colspan="2">

                <input type="submit" value="提交"/>&nbsp;&nbsp;

                <input type="reset" value="重置"/>

            </td>

        </tr>

    </table>

</form>

</body>

</html>

处理上传文件的Servlet：

package com.yyq.servlet3.multipartconfig;

import javax.servlet.ServletException;

import javax.servlet.annotation.MultipartConfig;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.Part;

import java.io.File;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.UUID;

/**

 * Created by gao on 16-4-14.

 */

@WebServlet(name = "upFile", urlPatterns = {"/uploadfile"})

@MultipartConfig(maxFileSize = 500000, maxRequestSize = -1)

public class FileUploadServlet extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //resp.setContentType("text/html;charset=utf-8");

        //获取请求参数值

        Part part = req.getPart("file");

        //存储路径

        String storePath = req.getServletContext().getRealPath("/temp");

        //Servlet3没有提供直接获取文件名，后缀名的方法，需要从请求头中解析出来

        //获取请求头

        String header = part.getHeader("content-disposition");

        //获取文件后缀名

        //String suffix = parseFileName(header);

        String name = parseFileName(header);

        //重新命名

        //String name = UUID.randomUUID() + suffix;

        //把文件写到指定路径

        part.write(storePath + File.separator + name);

//        PrintWriter out = resp.getWriter();

//        out.println("上传成功");

//        out.flush();

//        out.close();

        //获得文件描述信息

        String description = req.getParameter("description");

        req.setAttribute("f", name);

        req.setAttribute("des", description);

        req.getRequestDispatcher("info.jsp").forward(req, resp);

    }

    /*

    *根据请求头解析出上传文件的后缀名称

    */

    /**

     * 根据请求头解析出文件名

     * 请求头的格式：火狐和google浏览器下：form-data; name="file"; filename="snmp4j--api.zip"

     * IE浏览器下：form-data; name="file"; filename="E:\snmp4j--api.zip"

     *

     * @param header 请求头

     * @return 文件名

     */

    public String parseFileName(String header) {

        //return header.substring(header.lastIndexOf("."), header.length() - 1);

        /**

         * String[] tempArr1 = header.split(";");代码执行完之后，在不同的浏览器下，tempArr1数组里面的内容稍有区别

         * 火狐或者google浏览器下：tempArr1={form-data,name="file",filename="snmp4j--api.zip"}

         * IE浏览器下：tempArr1={form-data,name="file",filename="E:\snmp4j--api.zip"}

         */

        String[] tempArr1 = header.split(";");

        /**

         *火狐或者google浏览器下：tempArr2={filename,"snmp4j--api.zip"}

         *IE浏览器下：tempArr2={filename,"E:\snmp4j--api.zip"}

         */

        String[] tempArr2 = tempArr1[2].split("=");

        //获取文件名，兼容各种浏览器的写法

        String fileName = tempArr2[1].substring(tempArr2[1].lastIndexOf("\\") + 1).replaceAll("\"", "");

        return fileName;

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

显示上传文件和描述信息的页面info.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" pageEncoding="UTF-8" %>

<%

    String path = request.getContextPath();

    String basePath = request.getScheme() + "://" + request.getServerName() + ":"

            + request.getServerPort() + path +"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

    <title>Servlet3.0 上传文件</title>

</head>

<body>

    <h3><%=request.getAttribute("des")%></h3>

    <img alt = "servlet3" src="<%=basePath %>temp/<%=request.getAttribute("f")%>">

</body>

</html>
2、异步处理支持
    Servlet3.0支持异步处理支持，Servlet接收到请求之后，可能首先需要对请求携带的数据进行一些预处理；接着，Servlet线程将请求转交给一个异步线程来执行业务处理，线程本身返回至容器，此时Servlet还没有生成响应数据，异步线程处理完业务以后，可以直接生成响应数据（异步线程拥有ServletRequest和ServletResponse对象的引用），或者将请求继续转发给其他Servlet。
    1）对于使用传统的部署描述文件web.xml配置Servlet和过滤器的情况，Servlet3.0为<servlet>和<filter>标签增加了<async-supported>子标签，该标签的默认取值为false，要启用异步处理支持，则将其设为true即可。 
<servlet>

    <servlet-name>DemoServlet</servlet-name>

    <servlet-class>com.yyq.servlet3.asyncsupported.AsyncDemoServlet</servlet-class>

    <async-supported>true</async-supported>

</servlet>

2）对于使用Servlet3.0提供的@WebServlet和@WebFilter进行Servlet或过滤器配置的情况，这两个标注都提供了asyncSupported属性，默认该属性的取值为false，要启动异步处理支持，只需将该属性设置为true即可。

package com.yyq.servlet3.asyncsupported;

import javassist.bytecode.analysis.Executor;

import javax.servlet.AsyncContext;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.Date;

/**

 * Created by gao on 16-4-15.

 */

@WebServlet(urlPatterns = {"/asyncdemo"}, asyncSupported = true)

public class AsyncDemoServlet extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        out.println("进入Servlet的时间：" + new Date() + ".");

        out.flush();

        //在子线程中执行业务调用，并由其负责输出响应，主线程退出

        AsyncContext ctx = req.startAsync();

        new Thread(new Executor(ctx)).start();

        out.println("结束Servlet的时间：" + new Date() + ".");

        out.flush();

    }

    public class Executor implements Runnable {

        private AsyncContext ctx = null;

        public Executor(AsyncContext ctx) {

            this.ctx = ctx;

        }

        public void run() {

            try {

                //等待10秒钟，以模拟业务方法的执行

                Thread.sleep(10000);

                PrintWriter out = ctx.getResponse().getWriter();

                out.println("业务处理完毕的时间：" + new Date() + ".");

                out.flush();

                ctx.complete();

            }catch (Exception e){

                e.printStackTrace();

            }

        }

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

启动Tomcat，输入：http://localhost:8080/asyncdemo

Servlet3.0的新特性

3、可插性支持
    Servlet3.0新增的可插性（Pluggability）支持则将Servlet配置的灵活性提升到了新的高度。使用该特性，现在我们可以在不修改已有Web应用的前提下，只需将按照一定格式打包成的JAR包放到WEB-INF/lib目录下，即可实现新的功能的扩充，不需要额外的配置。Servlet3.0引入了称为“Web模块部署描述文件片段”的web-fragment.xml来实现可插性的。web-fragment.xml部署描述文件可以定义一切可以在web.xml中定义的内容。
1）新建的Servlet类：
package com.yyq.servlet3.pluggability;

import javax.naming.NamingException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;

/**

 * Created by gao on 16-4-15.

 */

public class FragmentDemoServlet extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        out.println("这是我Servlet3.0的第一个可插性示例");

        out.flush();

    }

    @Override

    public void destroy() {

        //空

    }

    @Override

    public void init() throws ServletException {

        //空

    }

}

2）在web目录下新建一个目录META-INF，在该目录下新建一个web-fragment.xml模块部署描述符文件片段：

<?xml version="1.0" encoding="UTF-8"?>

<web-fragment

        xmlns="http://java.sun.com/xml/ns/javaee"

        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

        version="3.0"

        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

    http://java.sun.com/xml/ns/javaee/web-fragment_3_0.xsd"

        metadata-complete="true">

    <!--给当前配置文件定义一个名称-->

    <name>FragmentA</name>

    <servlet>

        <servlet-name>fragmentDemo</servlet-name>

        <servlet-class>com.yyq.servlet3.pluggability.FragmentDemoServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>fragmentDemo</servlet-name>

        <url-pattern>/fragment</url-pattern>

    </servlet-mapping>

</web-fragment>
3）将FragmentDemoServlet和META-INF目录一起打包成JAR包，假如JAR包叫fragment.jar。
4）将fragment.jar放到其他Web项目中的WEB\lib目录中，然后访问http://localhost:8080/fragment即可。

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