需求：

service层中某个service对象service01方法执行时，需要对执行对象的权限进行判别，没有权限者不予执行权力。

思路：

在service类的该方法上进行注解，运用工厂产生这个service类代理对象service01，代理对象在该方法被调用时利用反射判断service01是否有权限注解，再根据权限注解来决定是否执行该方法

代码：

Permission注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Permission {

    int value();

}

被注解的方法

public interface BusinessService {
    @Permission(1)
    public void method01();
    
    public void method02();
}

public class BusinessServiceImp implements BusinessService {
    @Permission(1)
    @Override
    public void method01() {
        System.out.println("测试方法01");
    }

    @Override
    public void method02() {
        System.out.println("测试方法02");
    }

}

工厂类产生代理

public class ServiceFactory {
    private ServiceFactory() {}
    private static ServiceFactory instance = new ServiceFactory();
    public static ServiceFactory getInstance() {
        return instance;
    }
    
    public BusinessService createBusinessService(User user) {
        BusinessService service = new BusinessServiceImp();
        
        //产生代理对象并且返回
        return (BusinessService) Proxy.newProxyInstance(ServiceFactory.class.getClassLoader(), service.getClass().getInterfaces(), new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //得到要调用的方法的注解
                Permission per = method.getAnnotation(Permission.class);
                //如果没有注解
                if(per == null) {
                    System.out.println("没有注解");
                    return method.invoke(service, args);
                }
                //在这里如果user的id与注解相同，就是拥有该权限
                if(user.getId()==per.value()) {
                    System.out.println("权限正确");
                    return method.invoke(service, args);
                }
                //id与注解不同
                System.out.println("您没有该方法的执行权限");
                return null;
            }
        });
    }
}

代理对象中用到的user类

public class User {
    private int id;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }
    
}

测试类

public class ExecutionServlet {

    @org.junit.Test
    public void Test() {
        User user01 = new User();
        user01.setId(1);
        ServiceFactory fac01 = ServiceFactory.getInstance();
        BusinessService bus01 = fac01.createBusinessService(user01); 
        
        User user02 = new User();
        user02.setId(2);
        ServiceFactory fac02 = ServiceFactory.getInstance();
        BusinessService bus02 = fac02.createBusinessService(user02); 
        
        User user03 = new User();
        user03.setId(1);
        ServiceFactory fac03 = ServiceFactory.getInstance();
        BusinessService bus03 = fac03.createBusinessService(user03); 

        
        bus01.method01();//权限正确 测试方法01

        bus02.method01();//您没有该方法的执行权限

        bus03.method02();//没有注解 测试方法02
    }
}