Servlet学习（3）—— 服务器内部转发和客户端重定向

原创已于 2022-03-27 20:51:51 修改 · 1.6k 阅读

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于 2022-03-26 20:41:59 首次发布

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本文详细解析了服务器内部转发与客户端重定向的区别。通过具体的Java Servlet实例代码，阐述了一次请求-响应过程中的服务器内部转发机制，以及两次请求-响应过程中的客户端重定向机制。

一. 服务器内部转发

req.getRequestDispatcher("地址").forward(req,resp);

客户端发出请求（地址指向Servlet1），该请求由Servlet1接收，然后Servlet1将请求转发到Servlet2，由Servlet2执行请求，执行完后将响应的数据发送给客户端。

是一次请求-响应的过程，服务器内部经过了多少次转发，客户端是不知道的，地址栏不变。

package ServletStudy;

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

public class Servlet1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet1");
        req.getRequestDispatcher("/servlet2").forward(req,resp);
    }
}

package ServletStudy;

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

public class Servlet2 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet2");
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <servlet>
        <servlet-name>Servlet1</servlet-name>
        <servlet-class>ServletStudy.Servlet1</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Servlet1</servlet-name>
        <url-pattern>/servlet1</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>Servlet2</servlet-name>
        <servlet-class>ServletStudy.Servlet2</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Servlet2</servlet-name>
        <url-pattern>/servlet2</url-pattern>
    </servlet-mapping>
</web-app>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action = "http://localhost:8080/WebStudy_war_exploded/servlet1" method = "post">
        <input type = "submit" value = "提交"/>
    </form>
</body>
</html>

二. 客户端重定向

resp.sendRedirect("地址")

客户端发出请求（地址指向Servlet1），该请求由Servlet1接收，然后Servlet1对客户端进行响应，告诉客户端新的地址（即Servlet2的地址）。客户端重新发起请求（地址指向Servlet2），该请求由Servlet2接收，执行完后将响应的数据发送给客户端。

是两次请求-响应的过程，客户端知道url的变化，地址栏会变化。

package ServletStudy;

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

public class Servlet1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet1");
        resp.sendRedirect("/WebStudy_war_exploded/servlet2");   
    }
}

package ServletStudy;

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

public class Servlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Servlet2");
    }
}