优化Servlet：（利用反射的思想）

1.创建BaseServlet （重写父类的service方法）

package com.learning.web.servlet;

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

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

public class BaseServlet extends HttpServlet {

    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        //利用反射得到要执行的方法
        HttpServletRequest request=(HttpServletRequest) req;
        HttpServletResponse response=(HttpServletResponse) res;

        String method=request.getParameter("method");
        try {
            //得到名称为method的方法
            Method m = this.getClass().getDeclaredMethod(method, HttpServletRequest.class,HttpServletResponse.class);
            m.invoke(this, request,response);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

    }

}

2.总控制的Servlet继承BaseServlet

package com.learning.web.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.learning.domain.User;
import com.learning.exception.UserException;
import com.learning.service.UserService;

@WebServlet("/user")
public class UserServlet extends BaseServlet {
    private static final long serialVersionUID = 1L;

    //登录
    protected void login(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        UserService userService=new UserService();

        try {
            User user=userService.findUserByUsernameAndPassword(username,password);
            if (user!=null) {

                request.getSession().setAttribute("user", user);
                request.getRequestDispatcher("/index.jsp").forward(request, response);
                return;
            }
            request.setAttribute("login_msg", "用户名或密码错误");

        } catch (UserException e) {
            e.printStackTrace();
            request.setAttribute("login_msg", e.getMessage());
        }
        request.getRequestDispatcher("/login.jsp").forward(request, response);

    }

    //注销
    protected void logout(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.getSession().invalidate();
        response.sendRedirect(request.getContextPath()+"/index.jsp");
    }

}