java Servlet achieve and forwarding, redirection

First, implement the interface Servlet

package com.example.demo.servlet;

import javax.servlet.*;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import java.io.IOException;

@WebServlet(name = "myServlet", urlPatterns = "/myServlet",initParams = {
        @WebInitParam(name = "p1", value = "param1"),
        @WebInitParam(name = "p2", value = "param2")
})
public class MyServlet implements Servlet {

    private  ServletConfig config;

    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.err.println("初始化Servlet。。。");
        this.config=servletConfig;
        String name=config.getServletName();
        System.err.println("Servlet别名："+name);
        System.err.println("初始化参数1："+config.getInitParameter("p1"));
        System.err.println("初始化参数2："+config.getInitParameter("p2"));
    }

    @Override
    public ServletConfig getServletConfig() {
        System.err.println("获取Servlet配置。。。");
        return config;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.err.println("处理业务。。。");
        //防止中文乱码
        servletResponse.setContentType("text/html;charset=utf-8");
        //写出到浏览器
        servletResponse.getWriter().write("myServlet...厉害了");
    }

    @Override
    public String getServletInfo() {
        System.err.println("获取Servlet信息。。。");
        return "我是Servlet信息";
    }

    @Override
    public void destroy() {
        System.err.println("销毁Servlet。。。");
    }
}

Run the project, the request path http: // localhost: 81 / myServlet . Browser results:

console print the results:

Initialization Servlet. . .
Servlet Aliases: myServlet
initialization parameter 1: param1
initialization parameter 2: param2
processing operations. . .

Second, inherited HttpServlet class

package com.example.demo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //防止中文乱码
        response.setContentType("text/html;charset=utf-8");
        //写出到浏览器
        response.getWriter().write("firstServlet...厉害了");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

Run the project, visit http: // localhost: 81 / firstServlet. Browser results:

Third, Redirects and Forwards

1, redirection

package com.example.demo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向到http://localhost:81/myServlet(下面两句话是一个意思)
//        response.sendRedirect("myServlet");
        response.sendRedirect("http://localhost:81/myServlet");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

Request http: // localhost: 81 / firstServlet . Look developer tools, found carried out two requests. First request firstServlet, then re-request myServlet.

Console:

Initialization Servlet. . .
Servlet Aliases: myServlet
initialization parameter 1: param1
initialization parameter 2: param2
processing operations. . .
Processing business. . .

2, forward

package com.example.demo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //转发到http://localhost:81/myServlet
        request.getRequestDispatcher("myServlet").forward(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

Request http: // localhost: 81 / firstServlet . Look developer tools, we found only requested firstServlet, but the content of the request returns myServlet.

Response Contents:

Redirect to access external resources, can not be forwarded. Here redirected to Baidu.

package com.example.demo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向到百度
        response.sendRedirect("https://www.baidu.com/");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

Browser results