Request forwarding and redirection

There is login verification and display home page in the web page , How to jump and interact ？

Two Servlet（JSP） There are two ways to jump between ：

• Request forwarding
• Response redirection

One 、 Request forwarding

It's a server jump , Only one request will be generated

//  Realize the function of request forwarding 
request.getRequestDispatcher("/direct/index").forward(request,response);

Request forwarding ： The address is direct/check
Console output

Two 、 Response redirection

Redirection is browser side jump , There will be two requests

 //  Response redirection needs to be increased contextPath 
 response.sendRedirect("/servlet_advanced/direct/index"); 

Response redirection ： The address is entered as direct/check
After resetting, the address changes to direct/index

Console output

3、 ... and 、 Set request custom properties

Request permission to create custom attributes

Set request properties

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

Get request properties

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

1、 Request forwarding

Request only once , Can get admin attribute

2、 Response redirection

Response redirection , Ask twice , First destroyed , Get the property value as null

Four 、 Program page

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(" User login successful ");
		request.setAttribute("username", "admin");
		//  Realize the function of request forwarding 
		request.getRequestDispatcher("/direct/index").forward(request,response);
		//  Response redirection needs to be increased 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 + ".");
	}
}