.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);
}
}