servlet转发包含 servlet转发、包含详解（七）
柳暗花明睡一觉 人气:0想了解servlet转发、包含详解（七）的相关内容吗，柳暗花明睡一觉在本文为您仔细讲解servlet转发包含的相关知识和一些Code实例，欢迎阅读和指正，我们先划重点：servlet,转发,包含，下面大家一起来学习吧。
本文为大家介绍了servlet转发、servlet包含，供大家参考，具体内容如下
1.什么是servlet转发？
servlet将用户的请求通过一组servlet来处理，每个servlet都有自己特定的职责，当该servlet完成自己的工作后将请求转发到下一个servlet来处理，这种通过不同servelet相互转发请求来完成对某个请求的处理过程就叫做servlet转发。
2.什么是servlet包含？
servlet包含就是源servlet将其他web组件（servlet，html,jsp）,生成的结果包含到自己的结果中。
3.为什么需要servlet转发和包含？
servlet对象是由Servlet容器创建，Servlet对象的Service（）方法是由servlet容器调用，servlet之间是不允许相互调用（servlet API 2.1以前版本可以）。但是我们又需要通过多个servlet组件协调完成任务，同时方便代码维护管理，提高开发效率。这样就可以需要servlet转发和包含的技术支持。
4、转发和包含的相同点
（1）都是对同一个请求对象处理，源组件和目标组件共享同一个ServletRequest对象和ServletResponse对象。
（2）目标组件都可以是servlet，jsp，html。
（3）都依赖javax,servlet.RequestDispatcher 接口。
5.RequestDIspatcher 对象
该接口表示请求分发器
（1）获取RequestDispatcher对象方法
调用ServletContext的getRequestDispather(String path)方法获得。
调用ServletRequest的getRequestDispather(String path)方法获得。
（2）两种方法的区别
ServletContext调用方法的参数必须为绝对路径，而ServletRequest调用方法参数可以是绝对路径也可以是相对路径。
6.请求转发案例
CheckServlet 类用于处理用户请求参数。
package com.learn;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* Created by Administrator on 2017/09/26.
*/
public class CheckServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String userName = req.getParameter("name");
String message = "";
if(userName == null){
message = "please input your name";
} else {
message = userName;
}
req.setAttribute("mess",message);
RequestDispatcher requestDispatcher = getServletContext().getRequestDispatcher("/out");
PrintWriter out = resp.getWriter();
out.print("before forward ");
System.out.println("before forward");
requestDispatcher.forward(req,resp);
out.print("after forward");
System.out.println("after forward");
out.close();
}
}
OutServlet 用于输出处理结果
package com.learn;
import org.json.HTTP;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* Created by Administrator on 2017/09/26.
*/
public class OutServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String message = (String) req.getAttribute("mess");
PrintWriter printWriter = resp.getWriter();
printWriter.print(message);
printWriter.close();
}
}
注意： 1.在转发之前不要提交响应结果。
2.转发过程中，源组件的响应结果不会返回，只会返回目标组件的响应结果。
web.xml配置
<servlet>
<servlet-name>check</servlet-name>
<servlet-class>com.learn.CheckServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>check</servlet-name>
<url-pattern>/check</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>out</servlet-name>
<servlet-class>com.learn.OutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>out</servlet-name>
<url-pattern>/out</url-pattern>
</servlet-mapping>
7.包含（include）案例
MainServlet 用于包含其他组件，并返回响应结果
package com.learn;
import javax.servlet.RequestDispatcher;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* Created by Administrator on 2017/09/26.
*/
public class MainServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
PrintWriter out = resp.getWriter();
out.println("<html><head><title>mainServlet</title></head>");
out.println("<body>");
ServletContext servletContext = getServletContext();
RequestDispatcher headDisPatcher = servletContext.getRequestDispatcher("/header.html");
RequestDispatcher greetDisPatcher = servletContext.getRequestDispatcher("/greet");
RequestDispatcher footeDisPatcher = servletContext.getRequestDispatcher("/footer.html");
headDisPatcher.include(req,resp);
greetDisPatcher.include(req,resp);
footeDisPatcher.include(req,resp);
out.print("</body></html>");
out.close();
}
}
header.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>header</title> </head> <body> <font size="6">Welcome to ab</font> </body> </html>
GreetServlet
package com.learn;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* Created by Administrator on 2017/09/26.
*/
public class GreetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
PrintWriter out = resp.getWriter();
out.print("hi! "+req.getParameter("name")+", <p>");
out.close();
}
}
footer.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>footer</title> </head> <body> <span>Thanks for stopping</span> </body> </html>
web.xm配置
<servlet> <servlet-name>main</servlet-name> <servlet-class>com.learn.MainServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>main</servlet-name> <url-pattern>/main</url-pattern> </servlet-mapping> <servlet> <servlet-name>greet</servlet-name> <servlet-class>com.learn.GreetServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>greet</servlet-name> <url-pattern>/greet</url-pattern> </servlet-mapping>
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