请求重定向(四种方法)

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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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