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。
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。
（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();
}
}
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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();
}
}
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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>
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7.包含（include）案例
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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();
}
}
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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>
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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();
}
}
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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>
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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>
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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快网idc。
原文链接：http://www.cnblogs.com/wwyx-xi/p/7599237.html
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