hello2 源码分析

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）

package javaeetutorial.hello2;    //这里没注释的基本同问候页面

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.";

    }
}