aop原理

2018-07-03

AOP原理

AOP:面向切面编程的原理是代理模式。

代理模式

一、静态代理

接口

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public interface Subject {
     public void request();
}

实现

public class RealSubject implements Subject {
     @Override
     public void request() {
         System.out.println("realSubject  execute request");
     }
 }

代理类

public class SubjectProxy implements Subject {
    public SubjectProxy(RealSubject realSubject) {
        this.realSubject = realSubject;
    }
    private RealSubject realSubject;
    @Override
    public void request() {
        System.out.println("before");
        try{
            realSubject.request();
            System.out.println("afterReturning");
        }catch (Exception e){
            System.out.println("AfterThrowing");;
            System.out.println("ex:"+e.getMessage());
            throw e;
        }finally{
            System.out.println("after");
        }
    }
}

调用

public class Client {
     public static void main(String[] args) {
         RealSubject realSubject = new RealSubject();
         SubjectProxy subjectProxy = new SubjectProxy(realSubject);
         subjectProxy.request();
     }
 }

二、动态代理

jdk 动态代理

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类：java.lang.reflect.Proxy
接口：InvocationHandler
只能基于接口进行动态代理

编写动态代理类

public class JdkProxySubject implements InvocationHandler {
 public JdkProxySubject(RealSubject realSubject) {
     this.realSubject = realSubject;
 }

 private RealSubject realSubject;

 @Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
     System.out.println("before");
     Object result = null;
     try{
        result= method.invoke(realSubject,args);
     }catch(Exception e){
         System.out.println("AfterThrowing");
         System.out.println("ex:"+e.getMessage());
         throw e;
     }finally{
         System.out.println("after");
     }
     return result;
 }
}

调用

public class Client {
 public static void main(String[] args) {
     Subject subject = (Subject) Proxy.newProxyInstance(Client.class.getClassLoader(), new Class[]{Subject.class}, new JdkProxySubject(new RealSubject()));
     subject.request();
 }
}

cglib 动态代理

public static getProxy(Class clazz,MethodInterceptor interceptor){
    Enhancer enhancer = new Enhancer();
    //生成指定类的子类，重写子类中的业务逻辑
    enhancer.setSuperclass(clazz);
    //通过方法反射调用目标方法
    enhancer.setCallback(interceptor);
     //创建子类对象
      enhancer.create();  
}

创建要织入代码的类，实现MethodInterceptor接口

public class DemoMethodIntereptor implements MethodInterceptor {
      @Override
      public Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
          System.out.println("before");
          Object result = null;
          try {
              result = methodProxy.invokeSuper(obj, args);
          } catch (Exception e) {
              System.out.println("afterThrowing");
              System.out.println("ex:" + e.getMessage());
          } finally {
              System.out.println("after");
          }
          return result;
      }
  }

调用端

public class Client {
     public static void main(String[] args) {
     	Enhancer enhancer =new Enhancer();
        enhancer.setSuperclass(RealSubject.class);
        enhancer.setCallback(new DemoMethodIntereptor());
        Subject subject = (Subject) enhancer.create();
        subject.request();
     }
}

jdk和cglib对比
1. jdk只能动态代理有接口的类
2. cglib基于继承方式实现代理，无法对static，private ，final类，方法代理。

spring 如何选择使用jdk，cglib进行代理类

如果目标对象实现了接口，则默认走jdk动态代理
如果目标对象没有实现接口，则采用Cglib进行动态代理

如果目标对象实现了接口，且强制Cglib代理，则使用Cglib代理。

@SpringBootApplication
//强制使用cglib代理
@EnableAspectJAutoProxy(proxyTargetClass=true)
public static void Application(){
    public static void main(String[]args){
        SpringApplication.run(Application.class,args);
    }
}

代理模式

一、静态代理

二、 动态代理

二、动态代理