请求转发和请求包含

请求转发和请求包含

RequestDispatcher rd = request.getRequestDispatcher("/AServlet");

请求转发
rd.forward(request,reponse);
请求包含
rd.include(request,reponse);

有时一个请求需要多个Servlet协作才能完成，所以需要在一个Servlet跳到另一个Servlet

• 一个请求跨多个Servlet，需要使用转发和包含
• 请求转发：由下一个Servlet完成响应体，当前Servlet可以设置响应头！（留头不留体）
• 请求包含：由俩个Servlet共同完成响应体（留头又留体）

• 无论是请求转发还是请求包含，都在一个请求范围内！使用同一个request和同一个reponse

  
  image.png

演示请求转发

package bao;

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 = "oneServlet")
public class oneServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, 
HttpServletResponse response) throws ServletException, IOException {
        System.out.println("OneServlet...");
        /*设置响应头*/
        response.setHeader("aaa","AAA");
        /*设置响应体*/
        response.getWriter().print("Hello!oneServlet");
        /*请求转发*/
        request.getRequestDispatcher("twoServlet").forward(request,response);

    }

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

    }
}

package bao;

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 = "twoServlet")
public class twoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, 
HttpServletResponse response) throws ServletException, IOException {
        System.out.println("twoServlet....");
        /*设置响应体*/
        response.getWriter().print("Hello!twoServlet");

    }

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

    }
}

编译有错误

request域

void setAttribute(String name,Object value)
Object getAttribute(String name,Object value)

• 同一请求范围内使用request.setAttribute(),request.getAttribute()来传值，前一个Servlet调用setAttribute()来保存值，后一个Servlet调用getAttribute()写值

演示请求包含

package bao;

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 = "oneServlet")
public class oneServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, 
HttpServletResponse response) throws ServletException, IOException {
        System.out.println("OneServlet...");
        /*设置响应头*/
        response.setHeader("aaa","AAA");
        /*设置响应体*/
        response.getWriter().print("aaaaaa");
        /*请求包含*/
        request.getRequestDispatcher("twoServlet").include(request,response);

    }

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

    }
}


package bao;

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 = "twoServlet")
public class twoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, 
HttpServletResponse response) throws ServletException, IOException {
        System.out.println("twoServlet....");
        /*设置响应体*/
        response.getWriter().print("Hello!twoServlet");

    }

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

    }
}

编译有错误

请求转发和重定向的区别

• 请求转发是一个请求一次响应，而重定向是俩次请求俩次响应
• 请求转发地址栏不变化，而重定向会显示后一个请求的地址
• 请求转发只能转发到本项目其他Servlet，而重定向不止能重定向到本项目其他Servlet，还能定向到其他项目
• 请求转发是服务端行为，只需给出转发的Servlet路径，而重定向需要给出requestURL路径，即包含项目名
  -请求转发和重定向是转发效率高，因为只有一次请求
• 需要地址栏发生变化，那么必须使用重定向
• 需要在下一个Servlet中获取request域中的数据，必须使用转发