利用反射实现Servlet公共类的抽取

一次请求的执行过程：

请求：发送请求地址-->到达web.xml中，找到地址对应的servlet类-->通过反射调用该类的构造函数，创建该servlet类的对象-->通过当前对象调用该servlet的init方法-->发现没有-->从其父类HttpServlet找init，还是没有-->再找其父类GenericServlet，有init，调用该init方法加载当前servlet类-->调用当前servlet的service方法-->发现没有，找父类HttpServlet-->父类有该方法，调用它，service中获取请求方式-->然后调用do post()方法，当前servlet的do post()方法-->最后销毁，调用disdroy。嗯，其实调用父类的init,service方法这种说貌似不妥，应该是调用继承自父类的这两个方法

对原本的service方法进行重写，利用反射调用子类的具体执行方法

 package com.jixh.ss.web.base;

 import java.io.IOException;
 import java.lang.reflect.Method;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 public class BaseServlet extends HttpServlet {

     private static final long serialVersionUID = 1L;

     @Override
     public void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // localhost:8080/store/productServlet?method=updateUser,url中必须带有所要调用的子类具体方法的方法名
         String method = req.getParameter("method");

         if (null == method || "".equals(method) || method.trim().equals("")) {
             method = "execute";
         }

         // 注意:此处的this代表的是子类的对象
         // System.out.println(this);
         // 子类对象字节码对象
         @SuppressWarnings("rawtypes")
         Class clazz = this.getClass();

         try {
             // 查找子类对象对应的字节码中的名称为method的方法.这个方法的参数类型是:HttpServletRequest.class,HttpServletResponse.class
             @SuppressWarnings("unchecked")
             Method md = clazz.getMethod(method, HttpServletRequest.class, HttpServletResponse.class);
             if(null!=md){
                 String jspPath = (String)md.invoke(this, req, resp);
                 if (null != jspPath) {
                     req.getRequestDispatcher(jspPath).forward(req, resp);
                 }
             }
         } catch (Exception e) {
             e.printStackTrace();
         }

     }

     // 默认方法
     public String execute(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         return null;
     }

 }

子类Servlet只进行具体的业务处理

 package com.jixh.ss.web.servlet;

 import java.util.List;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import com.jixh.peanut.domian.FirstMenu;
 import com.jixh.peanut.domian.User;
 import com.jixh.peanut.domian.UserPower;
 import com.jixh.peanut.service.MenueService;
 import com.jixh.peanut.service.UserService;
 import com.jixh.peanut.service.impl.MenueServiceImpl;
 import com.jixh.peanut.service.impl.UserServiceImpl;
 import com.jixh.peanut.util.DateUtils;
 import com.jixh.peanut.util.UUIDUtils;
 import com.jixh.peanut.web.base.BaseServlet;

 import net.sf.json.JSONObject;

 public class userServlet extends BaseServlet {
     private static final long serialVersionUID = 1L;

     // 修改用户
     public String updateUser(HttpServletRequest request, HttpServletResponse response) {
         try {
             // 允许跨域访问的响应头
             response.setHeader("Access-Control-Allow-Origin", "*");

             String username = request.getParameter("username");
             String password = request.getParameter("password");
             // 验证用户名密码
             UserService userService = new UserServiceImpl();
             User user = userService.userLoging(username, password);
             if (user != null) {
                 // 验证通过，进行下一步
                 String uid = (String) request.getSession().getAttribute("thisUser");
                 String utype = request.getParameter("utype");
                 int ustate = Integer.parseInt(request.getParameter("ustate"));
                 String powerIdArray = request.getParameter("powerIdArray");
                 System.out.println(uid+"=="+username + "==" + password + "==" + utype + "==" + ustate + "==" + powerIdArray);
                 //修改用户表
                 boolean result = userService.updateUser(uid, utype, ustate);
                 System.out.println("修改用户结果为"+result);
                 if(result) {
                     response.getWriter().write("success");
                 }else {
                     response.getWriter().write("faild");
                 }
             } else {
                 // 直接响应
                 response.getWriter().write("error");
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
         return null;
     }
 }