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。
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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
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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
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<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
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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
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<!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
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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
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<!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
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<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> |
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://www.cnblogs.com/wwyx-xi/p/7599237.html
