如何实现一个Servlet中的多个功能
Posted zyx110
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如何实现一个Servlet中的多个功能
前言：唉，打脸了，前脚刚说过要跟Servlet正式告别，后脚这不又来了，哈哈，总结出一点东西，纠结了一下还是做个分享吧，学习知识比面子重要，对吧，下回再也不约Servlet了。
需求分析
看下面代码，现在有一个UserServlet，里面有增删改查四个方法，按平常的思维，用一个Servlet实现一个功能，这没毛病，现在问题是一个Servlet中有四个功能，那这该如何去实现呢？
package com.my.servlet;
import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends HttpServlet
private UserService userService = new UserServiceImpl();
public String add(HttpServletRequest request,HttpServletResponse response)
userService.add();
request.setAttribute("mess","添加成功");
return "r:add.jsp";
public String delete(HttpServletRequest request,HttpServletResponse response)
userService.delete();
request.setAttribute("mess","删除成功");
return "f:add.jsp";
public String update(HttpServletRequest request,HttpServletResponse response)
userService.update();
request.setAttribute("mess","修改成功");
return "add.jsp";
public String query(HttpServletRequest request,HttpServletResponse response)
userService.query();
request.setAttribute("mess","查询成功");
return "add.jsp";
解决思维
解决这个问题其实也简单，再写一个FatherServlet继承于HttpServlet,在这个父类Servlet中的service()方法中通过请求参数判断要调用的子类UserServlet中的哪个方法并执行，可能说到这有些朋友不懂了，如何用参数去判断大家一看下面的代码就明白了，我主要解释一下大家的疑惑，子类UserServlet如何去调用父类FatherServlet中的service()方法，其实秘诀就在这个参数上，在访问UserSerlvet时带上请求参数，访问过来后UserServlet中没有解决参数的方法，所以他会在父类FatherServlet中寻找响应的方法，找到后执行，这是继承的，子类继承父类的方法没毛病吧，所以就解决了。
解决完这个问题后我还在service()方法中加了判断是重定向还是转发的思维，这个就友情赠送了，不说了，来，看代码：
FatherServlet
package com.my.servlet;
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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class FatherServlet extends HttpServlet
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
String m = req.getParameter("m");
if (m==null||"".equals(m))
throw new RuntimeException("参数不能为空");
Class c = this.getClass();
try
Method method = c.getMethod(m,HttpServletRequest.class,HttpServletResponse.class);
Object o =method.invoke(this,req,resp);
String rel =String.valueOf(o);
//判断返回值的前缀，默认转发，r:重定向 f:转发
if (rel.startsWith("r:"))
rel = rel.substring(rel.indexOf(":")+1);
resp.sendRedirect(rel);
else if(rel.startsWith("f:"))
rel = rel.substring(rel.indexOf(":")+1);
req.getRequestDispatcher(rel).forward(req,resp);
else
req.getRequestDispatcher(rel).forward(req,resp);
catch (NoSuchMethodException e)
throw new RuntimeException("请求的方法不存在！！");
catch (IllegalAccessException e)
throw new RuntimeException("请求方法执行异常！！");
catch (InvocationTargetException e)
throw new RuntimeException("请求方法执行异常！！");
UserServlet
package com.my.servlet;
import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends FatherServlet
private UserService userService = new UserServiceImpl();
public String add(HttpServletRequest request,HttpServletResponse response)
userService.add();
request.setAttribute("mess","添加成功");
return "r:add.jsp";
public String delete(HttpServletRequest request,HttpServletResponse response)
userService.delete();
request.setAttribute("mess","删除成功");
return "f:add.jsp";
public String update(HttpServletRequest request,HttpServletResponse response)
userService.update();
request.setAttribute("mess","修改成功");
return "add.jsp";
public String query(HttpServletRequest request,HttpServletResponse response)
userService.query();
request.setAttribute("mess","查询成功");
return "add.jsp";
完整演示
此篇主要是解决题目所示的需求，先在需求解决了，做戏还要做全呢，我就把我测试的代码都整理出来，方便新手去学习。
UserDao
package com.my.dao;
public interface UserDao
public void add();
public void delete();
public void update();
public void query();
UserDaoImpl
package com.my.dao.impl;
import com.my.dao.UserDao;
public class UserDaoImpl implements UserDao
@Override
public void add()
System.out.println("UserDao中的添加功能实现了");
@Override
public void delete()
System.out.println("UserDao中的删除功能实现了");
@Override
public void update()
System.out.println("UserDao中的修改功能实现了");
@Override
public void query()
System.out.println("UserDao中的查询功能实现了");
UserService
package com.my.service;
public interface UserService
public void add();
public void delete();
public void update();
public void query();
UserServiceImpl
package com.my.service.impl;
import com.my.dao.UserDao;
import com.my.dao.impl.UserDaoImpl;
import com.my.service.UserService;
public class UserServiceImpl implements UserService
private UserDao userDao = new UserDaoImpl();
@Override
public void add()
userDao.add();
@Override
public void delete()
userDao.delete();
@Override
public void update()
userDao.update();
@Override
public void query()
userDao.query();
UserServlet
package com.my.servlet;
import com.my.service.UserService;
import com.my.service.impl.UserServiceImpl;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/user")
public class UserServlet extends FatherServlet
private UserService userService = new UserServiceImpl();
public String add(HttpServletRequest request,HttpServletResponse response)
userService.add();
request.setAttribute("mess","添加成功");
return "r:add.jsp";
public String delete(HttpServletRequest request,HttpServletResponse response)
userService.delete();
request.setAttribute("mess","删除成功");
return "f:add.jsp";
public String update(HttpServletRequest request,HttpServletResponse response)
userService.update();
request.setAttribute("mess","修改成功");
return "add.jsp";
public String query(HttpServletRequest request,HttpServletResponse response)
userService.query();
request.setAttribute("mess","查询成功");
return "add.jsp";
FatherServlet
package com.my.servlet;
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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class FatherServlet extends HttpServlet
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
String m = req.getParameter("m");
if (m==null||"".equals(m))
throw new RuntimeException("参数不能为空");
Class c = this.getClass();
try
Method method = c.getMethod(m,HttpServletRequest.class,HttpServletResponse.class);
Object o =method.invoke(this,req,resp);
String rel =String.valueOf(o);
//判断返回值的前缀，默认转发，r:重定向 f:转发
if (rel.startsWith("r:"))
rel = rel.substring(rel.indexOf(":")+1);
resp.sendRedirect(rel);
else if(rel.startsWith("f:"))
rel = rel.substring(rel.indexOf(":")+1);
req.getRequestDispatcher(rel).forward(req,resp);
else
req.getRequestDispatcher(rel).forward(req,resp);
catch (NoSuchMethodException e)
throw new RuntimeException("请求的方法不存在！！");
catch (IllegalAccessException e)
throw new RuntimeException("请求方法执行异常！！");
catch (InvocationTargetException e)
throw new RuntimeException("请求方法执行异常！！");
add.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="z" uri="http://mycompany.com" %> <html> <head> <title>测试页面</title> </head> <body> <h1>测试</h1> $mess </body> </html>
测试展示
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