Request和Response学习笔记5

服务器内部请求的转发

这里请求传递所使用的方法：

// 通过request对象获取请求转发器对象
RequestDispatcher getRequestDispatcher(String path)

// 使用RequestDispatcher对象来进行转发
forward(ServletRequest request, ServletResponse response)

实例引入

创建一个Web项目：RequestDelivery

创建两个类，在这两个类之间进行请求的传递：

RequestDemo01.java

import javax.servlet.RequestDispatcher;
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("/demo01")
public class RequestDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("demo01被访问了！");
        // 获取请求发送对象
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/demo02");
        // 发送请求
        requestDispatcher.forward(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}

RequestDemo02.java

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("/demo02")
public class RequestDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("我是demo02，demo01的请求对象已经传递过来了！");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}

启动服务器，访问：http://localhost:8080/RequestDelivery_war_exploded/demo01

控制台输出：
```
demo01被访问了！
我是demo02，demo01的请求对象已经传递过来了！
```
页面不会跳转，还在在demo1页面。

特点

浏览器地址栏路径不发生变化
只能转发到当前服务器内部资源中。不能转发到其他服务器。
用户的发送请求是一次，被转发的请求也是用户发送的请求对象。

Request共享数据

备注：
- 域对象：一个有作用范围的对象，可以在一定范围内共享数据。
- request域：代表一次请求的范围，一般用于请求转发的多个资源中共享数据。

方法：

// 存储数据
void setAttribute(String name,Object obj)

// 通过键获取值
Object getAttitude(String name)

// 通过键移除键值对
void removeAttribute(String name)

实例引入

创建两类：

RequestDemo03.java

import javax.servlet.RequestDispatcher;
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("/demo03")
public class RequestDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("demo03被访问了！");
        // 获取请求发送对象
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/demo04");
        // 发送请求
        requestDispatcher.forward(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}

RequestDemo04.java

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("/demo04")
public class RequestDemo04 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("我是demo04，demo03的请求对象已经传递过来了！");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}

存储数据

修改RequestDemo03.java中的doGet()方法：

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    System.out.println("demo03被访问了！");
    // 存储数据到request域中
    request.setAttribute("Set's Message", "Hello, setAttribute!");

    // 获取请求发送对象
    RequestDispatcher requestDispatcher = request.getRequestDispatcher("/demo04");
    // 发送请求
    requestDispatcher.forward(request, response);
}

修改RequestDemo04.java中的doGet()方法：

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    System.out.println("我是demo04，demo03的请求对象已经传递过来了！");
    // 获取request域数据
    System.out.println(request.getAttribute("Set's Message"));
}

启动服务器，访问：http://localhost:8080/RequestDelivery_war_exploded/demo03

控制台输出：

demo03被访问了！
我是demo04，demo03的请求对象已经传递过来了！
Hello, setAttribute!

参考文献

无

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