本文為大家介紹了servlet轉發、servlet包含，供大家參考，具體內容如下
1.什么是servlet轉發？
servlet將用戶的請求通過一組servlet來處理，每個servlet都有自己特定的職責，當該servlet完成自己的工作后將請求轉發到下一個servlet來處理，這種通過不同servelet相互轉發請求來完成對某個請求的處理過程就叫做servlet轉發。
2.什么是servlet包含？
servlet包含就是源servlet將其他web組件（servlet，html,jsp）,生成的結果包含到自己的結果中。
3.為什么需要servlet轉發和包含？
servlet對象是由Servlet容器創建，Servlet對象的Service（）方法是由servlet容器調用，servlet之間是不允許相互調用（servlet API 2.1以前版本可以）。但是我們又需要通過多個servlet組件協調完成任務，同時方便代碼維護管理，提高開發效率。這樣就可以需要servlet轉發和包含的技術支持。
4、轉發和包含的相同點
?。?）都是對同一個請求對象處理，源組件和目標組件共享同一個ServletRequest對象和ServletResponse對象。
?。?）目標組件都可以是servlet，jsp，html。
?。?）都依賴javax,servlet.RequestDispatcher 接口。
5.RequestDIspatcher 對象
該接口表示請求分發器
?。?）獲取RequestDispatcher對象方法
調用ServletContext的getRequestDispather(String path)方法獲得。
調用ServletRequest的getRequestDispather(String path)方法獲得。
?。?）兩種方法的區別
ServletContext調用方法的參數必須為絕對路徑，而ServletRequest調用方法參數可以是絕對路徑也可以是相對路徑。
6.請求轉發案例
CheckServlet 類用于處理用戶請求參數。
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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 用于輸出處理結果
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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.在轉發之前不要提交響應結果。
2.轉發過程中，源組件的響應結果不會返回，只會返回目標組件的響應結果。
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 用于包含其他組件，并返回響應結果
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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內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：http://www.cnblogs.com/wwyx-xi/p/7599237.html
