请求转发与重定向

在网页中有登录校验与显示首页，如何进行跳转和交互？

两个Servlet（JSP）之间跳转有两种方式：

• 请求转发
• 响应重定向

一、请求转发

是服务器跳转，只会产生一次请求

// 实现了请求转发的功能
request.getRequestDispatcher("/direct/index").forward(request,response);

请求转发：地址为direct/check
控制台输出

二、响应重定向

重定向是浏览器端跳转，会产生两次请求

 // 响应重定向需要增加contextPath 
 response.sendRedirect("/servlet_advanced/direct/index"); 

响应重定向：地址输入为direct/check
重定向后地址变为direct/index

控制台输出

三、设置请求自定义属性

请求允许创建自定义属性

设置请求属性

request.setAttribute("username", "admin");

获取请求属性

String name = (String)request.getAttribute("username");

1、请求转发

只请求一次，可以获取admin属性

2、响应重定向

响应重定向，请求两次，第一次已销毁，获取属性值为null

四、程序页面

1、CheckLoginServlet.java

package com.ssyt.servlet.direct;

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 CheckLoginServlet */
@WebServlet("/direct/check")
public class CheckLoginServlet extends HttpServlet {
    
	private static final long serialVersionUID = 1L;
       
    /** * @see HttpServlet#HttpServlet() */
    public CheckLoginServlet() {
    
        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("用户登录成功");
		request.setAttribute("username", "admin");
		// 实现了请求转发的功能
		request.getRequestDispatcher("/direct/index").forward(request,response);
		// 响应重定向需要增加contextPath
		//response.sendRedirect("/servlet_advanced/direct/index");
	}
}

2、IndexServlet.java

package com.ssyt.servlet.direct;

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 IndexServlet */
@WebServlet("/direct/index")
public class IndexServlet extends HttpServlet {
    
	private static final long serialVersionUID = 1L;
       
    /** * @see HttpServlet#HttpServlet() */
    public IndexServlet() {
    
        super();
        // TODO Auto-generated constructor stub
    }

	/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
		String name = (String)request.getAttribute("username");
		response.getWriter().println("This is index page!current username is " + name + ".");
	}
}