请求转发与包含-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_34993631/article/details/52311331

1.域对象：这是一个请有求范围容器。
2.在实际的应用中通过ServletContext
对象来带数据是不行的，因为他是一个共享数据的操作。而是通过域对象来传递。
3.请求转发

Servlet部分
package hyl;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//请求转发，以及使用request域对象把数据带给转发资源
//特点：1.客户端只发送一次请求而服务器端有多个web资源被访问 2.客户端地址栏没有变化
//服务器自己内部Servlet的折腾
public class RequestDemo5 extends HttpServlet {

//web中的mvc （model   javabean） (view jsp) (cotrller servlrt)
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   String data = "dfasd";

   request.setAttribute("data", data);
   //将信息转发到jsp中
   request.getRequestDispatcher("/message.jsp").forward(request, response);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doGet(request,response);
}

}

jsp部分
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <base href="<%=basePath%>">

    <title>My JSP 'message.jsp' starting page</title>

</head>

<body>
   $(data)
   <%
   String data = (String)request.getAttribute("data");
   out.write(data);
    %>
</body>
</html>

4.关闭流的不能跳转的异常
package hyl;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RequestDemo2 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String data = "sdfaasdfa";

  PrintWriter writer = response.getWriter();
  writer.write(data);
  //writer.close();


  if(true){
  request.getRequestDispatcher("/message.jsp").forward(request, response);
  return;//在一次跳转之后一定要return，防止多次跳转抛异常
  }
  //在跳转之前是不能关闭的，否则会抛异常，关闭的时候我们想要的跳转就失败了,实现了跳转之后会自动清空response的内容
  request.getRequestDispatcher("/message.jsp").forward(request, response);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doGet(request,response);
}

}

5.上面提到了forward 还有一个是包含关系的转发就是includ

request.getRequestDispatcher("/message.jsp").includ(request, response);/mmmm
String data = "sdfaasdfa";

  PrintWriter writer = response.getWriter();
  writer.write(data);

request.getRequestDispatcher("/message.jsp").includ(request, response);/ffff

在网页里就能看到:
mmmm
ssdfaasdf
ffff
也就是把三个页面组合了起来，但是我们发现这不是一个正常的页面，所以在这里我们需要删除完整的jsp全局架构标签