请求重定向（四种方法）

转载 于 2014-11-30 17:08:41 发布 · 1.5w 阅读 · 8
文章标签：

#java web

本文详细解析了Web开发中请求转发与重定向的工作原理及使用场景。对比了转发与重定向的区别，包括浏览器地址栏的变化、响应头信息的处理等，并通过示例代码展示了具体的实现方法。

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.转发与重定向细节（实际开发中知道一个原则）

RequestDispatcher有包含和转发两种功能

1.请求转发（getRequestDispatcher("").forward(request,response)）

请求转发：由源组件转发到目标组件时，容器会清空源组件输出的数据，给目标干净的东西，所以用户只会看到目标组件输出的页码结果，

但是响应头信息是不清空的。

编码原则：不要在转发前后向后页面输出数据（不用功）

2.包含（动态包含）

(getRequestDispatcher("").include(request,response))

由源组件包含到目标组件时，容器会清空目标组件的头 。因此，源组件设置的头才有效。

但是，响应体信息是不清空的

编码原则：不要在目标组件中设置响应头（无用功）

===========================================^^^^^^^文章总结^^^^^^^^^==============================================================


-------------------------------->用response.sendRedirect()做转向其实是向浏览器发送一个特殊的Header，然后由浏览器来做转向，转到指定的页面，所以用sendRedirect时，浏览器的地址栏上可以看到地址的变化。（请求重定向）

package cn.ITHong.Response;


import java.io.IOException;




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


//请求重定向
public class ResponseDemo7 extends HttpServlet {



public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// response.setStatus(302);
// response.setHeader("location", "http://www.baidu.com");
response.sendRedirect("http://www.baidu.com");

}




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



}


}

-------------------------------------------------------     第二种 请求转发 ------------------------------------------------------------

-----------------------------------------        以下的浏览器地址栏不会改变还是         ----------------------------------------------

-----------------------------------------        本地址栏：http://localhost:8080/Web07/servlet/RequestDemo4 ------------

----------------------------------------       后地址栏： http://localhost:8080/Web07/servlet/RequestDemo4 ------------

------------------------------------------------------------------------------------------------------------>RequestDemo4.java（释放类）

package cn.ITHong.Request;

import java.io.IOException;


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

public class RequestDemo4 extends HttpServlet {


	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		request.setAttribute("p", "request");
		response.getWriter().write("释放完毕");
		RequestDispatcher rd =request.getRequestDispatcher("/servlet/RequestDemo5");
		rd.forward(request, response);
	
	}


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

}


------------------------------------------------------------------------------------------------------------->RequestDemo5.java(被重定向的类) 

package cn.ITHong.Request;


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 RequestDemo5 extends HttpServlet {


	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("UTF-8");
		String value =(String) request.getAttribute("p");
		response.getWriter().write(value.toString());
	}


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


		doGet(request, response);
	}


}

-------------------------------------------------------------------------------------------->第三种方法

总结：与第二种的区别

第三种：RequestDispatcher rd = ServletContext.getRequestDispatcher(目标资源的URI);

第二种:  RequestDispatcher rd = ServletRequest.getRequestDispatcher(目标资源的URI)；

区别：

方式三中的目标资源的URI 必须以“/”开头，不然报错，此斜线表示当前应用

   


方式二中的目标资源的URI 如果以“/”开头，表示当前应用（绝对路径表示法），如果不已“/”开头，   表示相对路劲

http://localhost:8080/Web07/servlet/RequestDemo5源

http://localhost:8080/Web07/servlet/RequestDemo6目标

则目标为RequestDemo6（相对源）


http://localhost:8080/Web07/servlet/RequestDemo5源

http://localhost:8080/Web07/servlet/a/RequestDemo6目标

则目标为a/RequestDemo6（相对源）



http://localhost:8080/Web07/servlet/RequestDemo5源

http://localhost:8080/Web07/RequestDemo6目标

则目标为../RequestDemo6（相对源）


package cn.ITHong.Request;

import java.io.IOException;



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

public class RequestDemo4 extends HttpServlet {


	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		request.setAttribute("p", "request");
		response.getWriter().write("释放完毕");
		
		ServletContext sc = getServletContext();
		RequestDispatcher rd =sc.getRequestDispatcher("/servlet/RequestDemo5");
		rd.forward(request, response);
	
	}


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

}

============================================================================================================

答案：只会在浏览器显示I'm eight   这个例子中 就像

只执行了 RequestDemo6.java.

具体：请求重定向

--------------------------------------------------------------------------------------------------------------------------RequestDemo6.java(源)

package cn.ITHong.Request;

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 RequestDemo6 extends HttpServlet {

	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		PrintWriter out = response.getWriter();
		out.print("seven forward before");//会执行，但是Httpservletquest内容会被清空
		
		request.getRequestDispatcher("/servlet/RequestDemo7").forward(request, response);//重定向
		out.print("seven forward after");<span style="font-family: Arial, Helvetica, sans-serif;">//会执行，但是Httpservletquest内容会被清空</span>

	}

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

}


--------------------------------------------------------------------------------------------------------------------------RequestDemo7.java(目标：重定向地址)

package cn.ITHong.Request;

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 RequestDemo7 extends HttpServlet {


	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		PrintWriter out = response.getWriter();
		out.print("I'm eight");
	
	}

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

	doGet(request, response);
	}

}



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