利用反射优化Servlet抽象出父类BaseServlet

　　在编写servlet的时候发现每个servlet里面的doPost方法都如：

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

　　而在doGet方法中大多是对uri的跳转   

　　(通过在uri后面加上method参数可以定位到不同的方法，这样就可以少写一些servlet了)

　　如果新增模块，则该模块的Servlet中也同样包含相同的代码，因此，代码过度冗余，需要优化。

protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获取客户端请求的方法名
        String methodName = request.getParameter("method");
        //根据名称判断调用的方法
        if("categoryList".equals(methodName))
        {
            categoryList(request,response);
        }else if("index".equals(methodName))
        {
            index(request,response);
        }else if("productInfo".equals(methodName))
        {
            productInfo(request,response);
        }else if("productList".equals(methodName))
        {
            productList(request,response);
        }
    }

　　抽象出父类BaseServlet，并且在BaseServlet中使用反射机制实现方法的调用

public class BaseServlet extends HttpServlet {
    private static final long serialVersionUID = 7978401768598506854L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1.获取方法名
        String methodName = request.getParameter("method");
        //2.得到请求Servlet的字节码
        Class clazz = this.getClass();
        try {
            //3.根据字节码和方法名获取方法对象 所有方法参数均为HttpServletRequest和HttpServletResponse类型
            Method method = clazz.getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.setAccessible(true);   //设置方法均直接访问
            //4.调用method方法,实现其中的功能
            method.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();
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }}

 　　然后再写servlet就只用写具体的方法就行了

@WebServlet("/user")
@SuppressWarnings("unused")
public class UserServlet extends BaseServlet {
    private static final long serialVersionUID = 7665438418738590582L;
    
    private UserService userService = new UserServiceImpl();
    
    //安全退出
    private void logout(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.getSession().invalidate();
        //涉及 - cookie  - 清除cookie
        response.sendRedirect(request.getContextPath() + "/index");
    }
    
    //用户登录
    private void login(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //自动登录  -  记住用户名
        
        User user = userService.login(username, password);
        if(user != null) {   //成功
            request.getSession().setAttribute("user", user); 
            response.sendRedirect(request.getContextPath() + "/index");
        } else {
            request.setAttribute("info", "用户名或密码错误!");
            request.getRequestDispatcher("/WEB-INF/jsp/login.jsp").forward(request, response);
        }
    }
    
    //email - 账号激活
    private void active(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String activeCode = request.getParameter("activeCode");
        userService.active(activeCode);
        request.setAttribute("info", "账号激活成功， 请登录！");
        request.getRequestDispatcher("/WEB-INF/jsp/login.jsp").forward(request, response); 
    }
    
    /**  
    * @Title: register  
    * @Description: 用户注册
    */
    private void register(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //调用service
        Map<String, String[]> paramMap = request.getParameterMap();
        userService.register(paramMap);
        
        //跳转至首页|登录页面
        request.getRequestDispatcher("/WEB-INF/jsp/registerSuccess.jsp").forward(request, response); 
    }

}