第 2 章 Servlet 编程

import javax.servlet.ServletException;
import java.io.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet
{
  //重写了父类HttpServlet中的doGet()方法，用于对GET请求方法做出响应
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
               throws ServletException,IOException
    {
         PrintWriter out = resp.getWriter();  //得到PrintWriter对象
         out.println("Hello Servlet");  //向客户端发送字符数据
         out.close(); 
    }
}

set classpath=%classpath%;D:\software\apache-tomcat-8.0.45\lib\servlet-api.jar

<?xml version="1.0" encoding="UTF-8"?>                  <!--XML声明-->
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
  http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 
  id="WebApp_ID" version="3.1">      <!--声明XML Schema的名称空间--> 
  <servlet>
        <servlet-name>helloworld</servlet-name>          <!--Servlet名称-->
        <servlet-class>HelloServlet</servlet-class>    <!--Servlet完全限定名-->
    </servlet>
  <servlet-mapping>
        <servlet-name>helloworld</servlet-name>           <!--Servlet名称-->
        <url-pattern>/myhello</url-pattern>         <!--Servlet的URL路径-->
    </servlet-mapping>    
</web-app>

Hello Servlet

public interface Servlet

public void init(ServletConfig config) throws ServletExeption {
    // 初始化代码...
}

public void service (ServletRequest request, ServletResponse response)
    throws ServletException, IOException {
}

public void doGet (HttpServletRequestrequest, HttpServletResponse response)
    throws ServletException, IOException {
    // Servlet代码
}

public void doPost (HttpServletRequest request,HttpServletResponse response)
    throws ServletException, IOException {
    // Servlet代码
}

public void destroy () {
    //清理代码...
}

package com.mialab.servlet_demo;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class LifeServlet
 */
@WebServlet(asyncSupported = true, urlPatterns = { "/LifeServlet" })
public class LifeServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LifeServlet() {
        super();
        // TODO Auto-generated constructor stub
    System.out.println(this.getClass().getName() + "的构造方法被调用");
    }
  /**
   * @see Servlet#init(ServletConfig)
   */
  public void init(ServletConfig config) throws ServletException {
    // TODO Auto-generated method stub
    System.out.println(this.getClass().getName() + "的init()方法被调用");
  }
  /**
   * @see Servlet#destroy()
   */
  public void destroy() {
    // TODO Auto-generated method stub
    System.out.println(this.getClass().getName() + "的destroy()方法被调用");
  }
  /**
   * @see HttpServlet#service(HttpServletRequest request, HttpServletResponse response)
   */
  //protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
  //}
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    response.getWriter().append("Served at: ").append(request.getContextPath());
    System.out.println(this.getClass().getName() + "的doGet()方法被调用");
  }
  /**
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    doGet(request, response);
  }
}

com.mialab.servlet_demo.LifeServlet的构造方法被调用
com.mialab.servlet_demo.LifeServlet的init()方法被调用
com.mialab.servlet_demo.LifeServlet的doGet()方法被调用

package javax.servlet;
...
public abstract class GenericServlet implements Servlet, ServletConfig,
    java.io.Serializable {
    ...
    //用 transient 关键字标记的成员变量不参与序列化过程
    private transient ServletConfig config;
    @Override
    public ServletConfig getServletConfig() {
        return config;
    }
    @Override
    public ServletContext getServletContext() {
        return getServletConfig().getServletContext();
    }
    @Override
    public String getInitParameter (String name) {
        return getServletConfig().getInitParameter(name) ;
    }
    @Override
    public void init (ServletConfig config) throws ServletException {
        this.config = config;
        this.init();
    }
    public void init() throws ServletException {
        // NOOP by default
    }
    ...
}

package javax .servlet.http;
...
    public abstract class HttpServlet extends GenericServlet {
        ...
        private static final String METHOD DELETE = "DELETE";
        private static final String METHOD HEAD = "HEAD"; 
        private static final String METHOD GET= "GET";
        private static final String METHOD OPTIONS = "OPTIONS";
        private static final String METHOD POST = "POST";
        private static final String METHOD PUT = "PUT";
        private static final String METHOD TRACE = "TRACE";
        protected void doGet (HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException{
            ...
        }
        protected void doPost (HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
            ...
        }
        //添加新的Service方法
        protected void service (HttpServletRequestreq, HttpServletResponseresp)
            throws ServletException, IOException {
            String method = req.getMethod();
            if (method.equals(METHOD_GET)) {
                ...
                    doGet (req, resp);
            } else if (method.equals(METHOD_HEAD)) {
                ...
                    doHead (req, resp);
            } else if (method.equals(METHOD_POST)) {
                doPost (req, resp);
            }else {...
                  }
        }
        //覆盖的Service方法
        @Override
        public void service (ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
            HttpServletRequest request;
            HttpServletResponse response;
            try {
                request F (HttpServletRequest) req;
                response = (HttpServletResponse) res;
            } catch (ClassCastException e) {
                throw new ServletException ("non-HTTP request or response") ;
            }
            service request, response);
        }
    }

package com.mialab.servlet_demo;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletConfigDemoServlet extends HttpServlet { 
  private ServletConfig servletConfig;
  
  @Override
    public void init(ServletConfig config) throws ServletException {
      this.servletConfig = config;
      System.out.println("-----------" + servletConfig + "-----------");
  }
    
    @Override
    public ServletConfig getServletConfig() {
        return servletConfig;
    }
    
    @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 使用ServletConfig对象获取初始化参数
    ServletConfig servletConfig = getServletConfig();
    System.out.println("-----------" + servletConfig + "-----------");
    String poet = servletConfig.getInitParameter("poet");
    String poem = servletConfig.getInitParameter("poem");
    // 设置响应到客户端的文本类型为HTML
    response.setContentType("text/html;charset=UTF-8");
    // 获取输出流
    PrintWriter out = response.getWriter();
    out.print("<p>获取ServletConfigDenoServlet的初始化参数：");
    out.println("</p><p>poet参数的值：" + poet);
    out.println("</p><p>poem参数的值：" + poem + "</p>");    
    out.append("Served at：").append(request.getContextPath());
  }
}

<servlet>
    <servlet-name>myServletConfig</servlet-name>
    <servlet-class>com.mialab.servlet_demo.ServletConfigDemoServlet</servlet-class>
    <init-param>
        <param-name>poet</param-name>
        <param-value>纳兰容若</param-value>
    </init-param>
    <init-param>
        <param-name>poem</param-name>
        <param-value>我是人间惆怅客</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>myServletConfig</servlet-name>
    <url-pattern>/myServletConfig</url-pattern>
</servlet-mapping>

http://localhost:8080/ServletDemo/myServletConfig

获取ServletConfigDemoServlet的初始化参数:
poet参数的值:纳兰容若
poem参数的值:我是人间惆怅客
Served at: /ServletDemo

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    // 设置响应到客户端的文本类型为HTML
    response.setContentType("text/html;charset=UTF-8");
    // 得到ServletContext对象
    ServletContext context = this.getServletContext();
    // 得到包含所有初始化参数名的Enumeration对象
    Enumeration<String> paramNames = context.getInitParameterNames();
    // 获取输出流
    PrintWriter out = response.getWriter();
    // 遍历所有的初始化参数名，得到相应的参数值，打印到控制台
    out.print("<h2>当前Web应用的所有初始化参数：</h2>");   
    // 遍历所有的初始化参数名，得到相应的参数值并打印
    while (paramNames.hasMoreElements()) {
        String name = paramNames.nextElement();
        String value = context.getInitParameter(name);
        out.println(name + "：" + value);
        out.println("<br>");
    }
    out.close();
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
    <display-name>ServletDemo</display-name>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <context-param>
        <param-name>username</param-name>
        <param-value>admin888</param-value>
    </context-param>
    <context-param>
        <param-name>password</param-name>
        <param-value>123456</param-value>
    </context-param>
    <context-param>
        <param-name>driverClassName</param-name>
        <param-value>org.postgresql.Driver</param-value>
    </context-param>
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://127.0.0.1:3306/test</param-value>
    </context-param>
    <servlet>
        <servlet-name>myServletConfig</servlet-name>
        <servlet-class>com.mialab.servlet_demo.ServletConfigDemoServlet</servlet-class>
        <init-param>
            <param-name>poet</param-name>
            <param-value>纳兰容若</param-value>
        </init-param>
        <init-param>
            <param-name>poem</param-name>
            <param-value>我是人间惆怅客</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>myServletConfig</servlet-name>
        <url-pattern>/myServletConfig</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>ErrorHandler</servlet-name>
        <servlet-class>com.mialab.servlet_demo.ErrorHandlerServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ErrorHandler</servlet-name>
        <url-pattern>/ErrorHandler</url-pattern>
    </servlet-mapping>
    <error-page>
        <error-code>404</error-code>
        <location>/ErrorHandler</location>
    </error-page>
    <error-page>
        <exception-type>java.lang.Throwable</exception-type>
        <location>/ErrorHandler</location>
    </error-page>
</web-app>

ServletContext context = this.getServletContext();
// 通过setAttribute()方法设置属性值
context.setAttribute("contextData", "Here is contexData");

PrintWriter out = response.getWriter();
ServletContext context = this.getServletContext();
// 获取文件绝对路径
String path = context.getRealPath("/WEB-INF/classes/data.properties");
FileInputStream in = new FileInputStream(path);
Properties pros = new Properties();
pros.load(in);
out.println("username = " + pros.getProperty("username") + "<br>");
out.println("password = " + pros.getProperty("password") + "<br>");
out.println("driverClassName = " + pros.getProperty("driverClassName") + "<br>");
out.println("url = " + pros.getProperty("url") + "<br>");

username=root
password=123456
driverClassName=org.postgresql.Driver
url=jdbc:mysql://127.0.0.1:3306/test

package com.mialab.servlet_demo;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/FormServlet")
public class FormServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public FormServlet() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        // 设置响应到客户端MIME类型和字符编码方式
        response.setContentType("text/html;charset=UTF-8");
        // 设置request对象的解码方式
        request.setCharacterEncoding("utf-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String sex = request.getParameter("sex");
        String home = request.getParameter("home");
        String info = request.getParameter("info");
        // 获取输出流
        PrintWriter out = response.getWriter();
        out.println("<p>用户名：" + username + "</p>");
        out.println("<p>密码：" + password + "</p>");
        out.println("<p>性别：" + sex + "</p>");
        out.println("<p>家乡：" + home + "</p>");
        out.println("<p>爱好：");
        // 获取参数名为“hobby”的值
        String[] hobbys = request.getParameterValues("hobby");
        for (int i = 0; i < hobbys.length; i++) {
            if (i < hobbys.length - 1)
                out.println(hobbys[i] + "，");
            else
                out.println(hobbys[i] + "");
        }
        out.println("</p>");
        out.println("<p>自我介绍：" + info + "</p>");
        out.close();
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        doGet(request, response);
    }
}

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Servlet处理表单数据</title>
    </head>
    <body>
        <h2>个人信息</h2>
        <hr>
        <form action="/ServletDemo/FormServlet" method="POST">
            <p>
                用户名：<input type="text" name="username">
            </p>
            <p>
                密 &nbsp;&nbsp;&nbsp;码 ：<input type="password" name="password">
            </p>
            <p>
                性 &nbsp;&nbsp;&nbsp;别 ：<input type="radio" name="sex" value="boy"
                                              checked>男<input type="radio" name="sex" value="girl">女
            </p>
            <p>
                家 &nbsp;&nbsp;&nbsp;乡 ：<select name="home"><option
                                                                   value="suzhou">苏州</option>
                <option value="shanghai">上海</option>
                <option value="nanjing">南京</option>
                </select>
            </p>
            <p>
                爱 &nbsp;&nbsp;&nbsp;好： <input type="checkbox" name="hobby"
                                              value="swim">游泳 <input type="checkbox" name="hobby"
                                                                     value="go">围棋 <input type="checkbox" name="hobby"
                                                                                          value="music">音乐
            </p>
            <p>
                自我介绍：<br>
                <textarea name="info" rows="5" cols="26"></textarea>
            </p>
            <p>
                <input type="submit" value="提交">
            </p>
        </form>
    </body>
    </body>
</html>

@WebServlet("/RedirectServlet")
public class RedirectServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        // 设置响应到客户端的文本类型为HTML
        response.setContentType("text/html;charset=UTF-8");
        // 输出当前时间
        response.getWriter().println(new java.util.Date());
        // 进行重定向
        response.sendRedirect(request.getContextPath() + "/AnotherServlet");
    }
}

@WebServlet("/AnotherServlet")
public class AnotherServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        // 设置响应到客户端的文本类型为HTML
        response.setContentType("text/html;charset=UTF-8");
        // 获取输出流
        PrintWriter out = response.getWriter();
        // 输出响应结果
        out.println("<p>重定向页面</p>");
        out.close();
    }
}

@WebServlet("/OtherServlet")
public class OtherServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        // 设置响应到客户端的文本类型为HTML
        response.setContentType("text/html;charset=UTF-8");
        // 从request对象中获取bookname属性值
        String bookname = (String) request.getAttribute("bookname");
        // 获取输出流
        PrintWriter out = response.getWriter();
        // 输出响应结果
        out.println("<p>请求转发的结果页面</p>");
        out.println("读取的request对象的bookname属性值为：" + bookname);
    }
}

/*
Navicat MySQL Data Transfer
Source Server         : mysql
Source Server Version : 50519
Source Host           : localhost:3306
Source Database       : book
Target Server Type    : MYSQL
Target Server Version : 50519
File Encoding         : 65001
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for book
-- ----------------------------
DROP TABLE IF EXISTS `book`;
CREATE TABLE `book` (
  `bookId` int(4) NOT NULL,
  `bookName` varchar(50) NOT NULL,
  PRIMARY KEY (`bookId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of book
-- ----------------------------
INSERT INTO `book` VALUES ('9801', 'Android应用开发实践教程');
INSERT INTO `book` VALUES ('9802', 'Web应用开发');
INSERT INTO `book` VALUES ('9803', 'iOS程序设计');

@WebServlet("/DataAccessServlet")
public class DataAccessServlet extends HttpServlet {
    // JDBC 驱动名及数据库 URL
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost:3306/book";
    // 数据库的用户名与密码，需要根据自己的设置
    static final String USER = "root";
    static final String PASS = "1";
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        Connection conn = null;
        Statement stmt = null;
        // 设置响应内容类型
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();   
        out.println("<h2>Servlet数据库访问</h2>");
        try {
            // 注册 JDBC 驱动器
            Class.forName("com.mysql.jdbc.Driver");
            // 打开一个连接
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            // 执行 SQL 查询
            stmt = conn.createStatement();
            String sql;
            sql = "select bookId,bookName from book";
            ResultSet rs = stmt.executeQuery(sql);
            // 展开结果集数据库
            while (rs.next()) {
                // 通过字段检索
                int bookId = rs.getInt("bookId");
                String bookName = rs.getString("bookName");       
                // 输出数据
                out.println("bookId：" + bookId);
                out.println("，bookName：" + bookName);       
                out.println("<br />");
            }
            //out.println("</body></html>");
            // 完成后关闭
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException se) {
            // 处理 JDBC 错误
            se.printStackTrace();
        } catch (Exception e) {
            // 处理 Class.forName 错误
            e.printStackTrace();
        } finally {
            // 最后是用于关闭资源的块
        }
    }
}

<!-- Servlet定义-->
    <servlet>
        <servlet-name>ErrorHandler</servlet-name>
        <servlet-class>ErrorHandler</servlet-class>
    </servlet>
    <!-- Servlet映射 -->
    <servlet-mapping>
        <servlet-name>ErrorHandler</servlet-name>
        <url-pattern>/ErrorHandler</url-pattern>
    </servlet-mapping>
    <!-- error-code相关的错误页面-->
    <error-page>
        <error-code>404</error-code>
        <location>/ErrorHandler</location>
    </error-page>
    <error-page>
        <error-code>403</error-code>
        <location>/ErrorHandler</location>
    </error-page>
    <!-- exception-type 相关的错误页面-->
    <error-page>
        <exception-type>
            javax.servlet.ServletException
        </exception-type >
        <location>/ErrorHandler</location>
    </error-page>
    <error-page>
        <exception-type>java.io.IOException</exception-type >
        <location>/ErrorHandler</location>
    </error-page>

<error-page>
  <exception-type>java.lang>Throwable</exception-type>
    <location>ErrorHandler</location>
</error-page>

public class ErrorHandlerServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        Throwable throwable = (Throwable) request.getAttribute("javax.servlet.error.exception");
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
        String servletName = (String) request.getAttribute("javax.servlet.error.servlet_name");
        if (servletName == null) {
            servletName = "Unknown";
        }
        String requestUri = (String) request.getAttribute("javax.servlet.error.request_uri");
        if (requestUri == null) {
            requestUri = "Unknown";
        }
        // 设置响应内容类型
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String title = "Servlet处理 Error/Exception";
        String docType = "<!DOCTYPE html>\n";
        out.println(
            docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body bgcolor=\"#f0f0f0\">\n");
        out.println("<h3>Servlet异常/错误处理</h3>");
        if (throwable == null && statusCode == null) {
            out.println("<h3>错误信息丢失</h2>");
            out.println("请返回 <a href=\"" + response.encodeURL("http://localhost:8080/") + "\">主页</a>。");
        } else if (statusCode != null) {
            out.println("错误代码 : " + statusCode + "<br><br>");
            out.println("Servlet Name : " + servletName + "</br></br>");
            out.println("异常类型 : " + throwable.getClass().getName() + "</br></br>");
            out.println("请求 URI: " + requestUri + "<br><br>");
            out.println("异常信息: " + throwable.getMessage());
        } else {
            //      out.println("<h3>错误信息</h3>");
            //      out.println("Servlet Name : " + servletName + "</br></br>");
            //      out.println("异常类型 : " + throwable.getClass().getName() + "</br></br>");
            //      out.println("请求 URI: " + requestUri + "<br><br>");
            //      out.println("异常信息: " + throwable.getMessage());
        }
        out.println("</body>");
        out.println("</html>");
    }
}

@WebServlet("/ExceptionServlet")
public class ExceptionServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        int x = 126/0;
        //int[] array = {2,4,6};
        //System.out.println(array[3]);
        //throw new ArrayIndexOutOfBoundsException();
    }
}

<servlet>
    <servlet-name>ErrorHandler</servlet-name>
    <servlet-class>com.mialab.servlet_demo.ErrorHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ErrorHandler</servlet-name>
    <url-pattern>/ErrorHandler</url-pattern>
</servlet-mapping>
<error-page>
    <error-code>404</error-code>
    <location>/ErrorHandler</location>
</error-page>
<error-page>
    <exception-type>java.lang.Throwable</exception-type>
    <location>/ErrorHandler</location>
</error-page>

@WebServlet(name = "/SimpleAsyncServlet", urlPatterns = { "/simpleAsync" }, asyncSupported = true)
public class SimpleAsyncServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        final AsyncContext asyncContext = request.startAsync();
        System.out.println(Thread.currentThread().getName());
        request.setAttribute("boyName", "李寻欢");
        asyncContext.setTimeout(6000);
        asyncContext.start(new Runnable() {
            @Override
            public void run() {
                try {
                    int millis = ThreadLocalRandom.current().nextInt(3000);
                    String currentThread = Thread.currentThread().getName();
                    System.out.println(currentThread + " sleep for " + millis + " milliseconds.");
                    Thread.sleep(millis);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                request.setAttribute("girlName", "我不是潘金莲");
                asyncContext.dispatch("/boygirl.jsp");
            }
        });
    }
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>访问Request域</title>
</head>
<body>
<p>Hello</p><hr>
<p>girlName：${girlName}</p>
<p>boyName：${boyName}</p>
</body>
</html>