【java web】

在Java web中 Servlet 是根基。虽然工作中几乎没人再去写Servlet了，框架为我们完成了这些工作。我们只要专注于业务逻辑的实现。但是理解Servlet还是很有必要的。

1. Servlet的架构图

Servlet Container 指的是Tomcat这样可以处理Servlet的服务器。

2. Servlet是怎么处理请求的？

做一个实验，首先用Eclipse新建一个项目，如下

需要我们自己编辑的有四个文件

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="LoginServlet" method="get">
<label>用户名</label>
<input name="username" type="text">
<br/>
<label>密码</label>
<input name="password" type="password">
<input type="submit" value="登陆">
</form>

</body>
</html>

doGet.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
Get Success
</body>
</html>

doPost.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
post success
</body>
</html>

着重讲一下LoginServlet.java，新建一个Servlet， Eclipse会默认生成doGet 和 doPost方法。 init()方法和destory()方法是从HttpServlet继承的，我们只做一个打印，直接调用HttpServlet的实现，这样不会影响Servlet的运行

package com.yeyeck.controller;

import java.io.IOException;
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 LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;
    
    
    @Override
    public void init() throws ServletException {
        System.out.println("init() worked");
        super.init();
    }
    
    
    @Override
    public void destroy() {
        System.out.println("destroy() worked");
        super.destroy();
    }
    
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("service() worked");
        super.service(req, resp);
    }
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doGet() worked");
        System.out.println("hash: " + this.hashCode());
        // TODO Auto-generated method stub
        System.out.println(request.getParameter("username"));
        System.out.println(request.getParameter("password"));
        response.sendRedirect("doGet.jsp");
//        response.getWriter().append("登陆成功");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        System.out.println("doPost() worked");
        System.out.println("hash: " + this.hashCode());
        System.out.println(request.getParameter("username"));
        System.out.println(request.getParameter("password"));
        response.sendRedirect("doPost.jsp");
    }

}

把项目部署到Tomcat跑起来，浏览器键入访问地址

会看到

右键检查，会看到表单现在的提交方式是get

在输入框内随便输入一些数据，提交。观察Eclipse控制台

页面跳转到

从控制台输出，我们可以看到，这次get请求，依次调用了 init()、service()、 doGet()方法

回到index，再请求一次，控制台显示

可以发现，第二次请求，只调用了 service() 和 doGet() 方法，并且两次打印的hash值是一样的

我们再把index.jsp的表单改成post方式提交, ctrl+save

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="LoginServlet" method="post">
<label>用户名</label>
<input name="username" type="text">
<br/>
<label>密码</label>
<input name="password" type="password">
<input type="submit" value="登陆">
</form>

</body>
</html>