1、GreetingServlet.java（问候页面）：
/**
* Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved.
*
* You may not modify, use, reproduce, or distribute this software except in
* compliance with the terms of the License at:
* https://github.com/javaee/tutorial-examples/LICENSE.txt
*/
package javaeetutorial.hello2; //指定包名
//导入程序库，使之成为可用的单元
import java.io.IOException; //导入捕获输入输出异常的包
import java.io.PrintWriter; //导入向文本输出流打印对象的格式化表示形式的包
import javax.servlet.RequestDispatcher; //导入将请求转发送到另一个资源功能的包，它可能是html，servlet或jsp等
import javax.servlet.ServletException; //导入servlet在遇到困难时可以抛出一般异常的包
import javax.servlet.annotation.WebServlet; //web服务中的，在Glassfish下lib中的包。
import javax.servlet.http.HttpServlet; //提供要进行子类化的抽象类，以创建适用于Web站点的HTTP Servlet
import javax.servlet.http.HttpServletRequest; //提供HTTP Servlet的请求信息
import javax.servlet.http.HttpServletResponse; //发送响应时提供特定于HTTP的功能
/**
* This is a simple example of an HTTP Servlet. It responds to the GET method of
* the HTTP protocol.
*/
@WebServlet("/greeting") //使用源文件中的注释@WebServlet servlet来设置servlet 的URL模式，此处将URL模式指定为/greeting
public class GreetingServlet extends HttpServlet { //创建一个继承父类HttpServlet的共有类GreetingServlet
@Override //当你想要覆写(重写)某个方法时，可以选择添加@Override这个注解,@Override 系统可以帮你检查方法的正确性
public void doGet(HttpServletRequest request, //重写该doGet方法，实现GETHTTP方法;HttpServletRequest包含客户端对servlet的请求的对象
HttpServletResponse response) //HttpServletResponse包含servlet发送给客户端的响应的对象
throws ServletException, IOException { //java.io.IOException如果在servlet处理GET请求时检测到输入或输出错误；ServletException如果无法处理GET请求
response.setContentType("text/html"); //发送给客户端浏览器的数据类型为html文件
response.setBufferSize(8192); //发送给客户端的响应对象的缓冲大小是8192
try (PrintWriter out = response.getWriter()) { //获取PrintWriter流，用来在客户端输出
out.println("<html lang="en">" //html标记语言用来显示页面
+ "<head><title>Servlet Hello</title></head>");
// then write the data of the response
out.println("<body bgcolor="#ffffff">"
+ "<img src="resources/images/duke.waving.gif" "
+ "alt="Duke waving his hand">"
+ "<form method="get">"
+ "<h2>Hello, my name is Duke. What's yours?</h2>"
+ "<input title="My name is: " type="text" "
+ "name="username" size="25"/>"
+ "<p></p>"
+ "<input type="submit" value="Submit"/>"
+ "<input type="reset" value="Reset"/>"
+ "</form>");
String username = request.getParameter("username"); //定义一个字符串username，把从request中拿出的username的值赋给它
if (username != null && username.length() > 0) { //如果username不为空且长度大于0
RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher("/response"); //通过绝对路径实现Servlet之间的请求传递（页面跳转）
if (dispatcher != null) {
dispatcher.include(request, response);//如果接收到的客户端的请求不为空时，记录保留request和response，以后不能再修改response里表示状态的信息
}
}
out.println("</body></html>");
}
}
@Override
public String getServletInfo() { //定义一个共有类getServletInfo方法获取网页的说明信息
return "The Hello servlet says hello.";
}
}
2、ResponseServlet.java（响应页面）
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;
/**
* This is a simple example of an HTTP Servlet. It responds to the GET
* method of the HTTP protocol.
*/
@WebServlet("/response")
public class ResponseServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
try (PrintWriter out = response.getWriter()) {
String username = request.getParameter("username");
if (username != null && username.length() > 0) { //判断当输入的username不为空且长度大于0，则打印Hello username
out.println("<h2>Hello, " + username + "!</h2>");
}
}
}
@Override
public String getServletInfo() {
return "The Response servlet says hello.";
}
}