BaseServlet 优化 - 反射实现方法自动执行

曾经终败给现在 2023-07-18 11:16 6阅读 0赞

实现需求：优化 Servlet 不需要一个个 action 的判断，以后根据 action 的值自动让方法名一样的方法自动执行。

**1、需要优化的 servlet ↓**

@WebServlet(name = "UserServlet",urlPatterns = "/UserServlet")
    public class UserServlet extends BaseServlet { 
        private UserService service = new UserService();
    
        /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String action = request.getParameter("action"); if ("register".equals(action)) { register(request,response); }else if("login".equals(action)){ login(request,response); }else if ("getUserLoginData".equals(action)){ getUserLoginData(request,response); }else if ("loginOut".equals(action)){ loginOut(request,response); } }*/
    
        private void loginOut(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            request.getSession().invalidate();
    
            response.sendRedirect("login.html");
        }
    
        private void getUserLoginData(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            Object user = request.getSession().getAttribute("loginUser");
            String loginData = new ObjectMapper().writeValueAsString(user);
            response.getWriter().write(loginData);
        }
    
        private void login(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            try { 
                // 获取前端的用户名和密码
                String username = request.getParameter("username");
                String password = request.getParameter("password");
    
                // 效验验证码
                String sessionCheckcode = (String) request.getSession().getAttribute("CHECKCODE_SERVER");
                String check = request.getParameter("check");
    
                if (!sessionCheckcode.equalsIgnoreCase(check)) { 
                    throw new CustomerErrorMsgException("验证码有误！");
                }
    
                // 去数据库查找是否有此用户
                User user = service.login(username, password);
                if (user == null) { 
                    throw new CustomerErrorMsgException("用户名或密码错误");
                }
    
                // 将登录用户存入会话域，会话域作用范围：同一个浏览器的打开至关闭 。
                request.getSession().setAttribute("loginUser",user);
                response.getWriter().print("true");
    
            } catch (CustomerErrorMsgException e) { 
                response.getWriter().print(e.getMessage());
            }catch (Exception e) { 
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
    
        private void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            try { 
    
                User user = new User();
                BeanUtils.populate(user,request.getParameterMap());
    
                String sessionCheckcode = (String) request.getSession().getAttribute("CHECKCODE_SERVER");
                String check = request.getParameter("check");
    
                if (!sessionCheckcode.equalsIgnoreCase(check)) { 
                    throw new CustomerErrorMsgException("验证码有误！");
                }
    
                boolean result = service.register(user);
                response.getWriter().print(result);
    
    
            }catch (CustomerErrorMsgException e) { 
                response.getWriter().write(e.getMessage());
            } catch (Exception e) { 
                e.printStackTrace();
            }
        }
    
    }

**优化方案：写一个父类 让 需要优化的类 继承它，在父类重写 HttpServlet 的 public void service 方法，通过反射执行子类与 action 值相同方法名的方法 ，实例 ↓**

import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.lang.reflect.Method;
    
    @WebServlet(name = "BaseServlet", urlPatterns = "/BaseServlet")
    public class BaseServlet extends HttpServlet { 
    
    
       //1.让所有请求先走父类处理请求方法
        @Override
        public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { 
            try { 
                
                //目标：使用反射实现根据方法名字字符串，让方法对象自动执行
    
                //将父接口转换为子接口
                HttpServletRequest request = (HttpServletRequest) req;
                HttpServletResponse response = (HttpServletResponse) res;
    
                //获取方法名
                String methodName = request.getParameter("action");
    
                //获取字节码对象
                Class clazz = this.getClass();
    
                //字节码Class对象根据方法名字与方法参数类型对象获取方法对象
                Method method = clazz.getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
                method.setAccessible(true);
    
                //让方法对象自动执行
                method.invoke(this,request,response);
            } catch (Exception e) { 
                e.printStackTrace();
                throw new RuntimeException(e);
            }
    
        }
    
    }