spring AOP

1.InvocationHandler

用于接口的代理，拦截。

首先一个接口和一个实现类：

public interface InvocationService {
    public void print();
}

public class InvocationServiceImpl implements InvocationService {
    @Override
    public void print() {
        System.out.println("real service print content");
    }
}

接着数写一个代理类并实现invocationHandler接口，充重写invoke方法：

public class InvocationServiceHandler implements InvocationHandler {

    private InvocationService invocationService;

    public InvocationServiceHandler(InvocationService invocationService) {
        this.invocationService = invocationService;
    }

    public InvocationService getProxy() {
        return (InvocationService) Proxy.newProxyInstance(invocationService.getClass().getClassLoader(), invocationService.getClass().getInterfaces(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("handler before method");
        Object invoke = method.invoke(invocationService, args);
        System.out.println("handler after method");
        return invoke;
    }
}

最后开始使用

public class HandlerMain {
    public static void main(String[] args) {
        InvocationServiceHandler handler = new InvocationServiceHandler(new InvocationServiceImpl());
        InvocationService proxy = handler.getProxy();
        proxy.print();
    }
}

分析一下Proxy.newProxyInstance（）是怎么返回这个代理对象的

/**
     * Returns an instance of a proxy class for the specified interfaces
     * that dispatches method invocations to the specified invocation
     * handler. 
     * 返回一个代理对象的实例,这个实例会把你给定的接口的方法转发到代理的方法中（接口下的所有方法和所实实现类）
     */
    @CallerSensitive
    public static Object newProxyInstance(ClassLoader loader,
                                          Class[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {
        Objects.requireNonNull(h);

        final Class[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {    //主要是检查权限 包的权限 修饰符的权限
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }

        /*
         * Look up or generate the designated proxy class.
         */
        Class cl = getProxyClass0(loader, intfs);

        /*
         * Invoke its constructor with the designated invocation handler.
         */
        try {
            if (sm != null) {
                checkNewProxyPermission(Reflection.getCallerClass(), cl);
            }

            final Constructor cons = cl.getConstructor(constructorParams);
            final InvocationHandler ih = h;
            if (!Modifier.isPublic(cl.getModifiers())) {
                AccessController.doPrivileged(new PrivilegedAction() {
                    public Void run() {
                        cons.setAccessible(true);
                        return null;
                    }
                });
            }
            return cons.newInstance(new Object[]{h});
        } catch (IllegalAccessException|InstantiationException e) {
            throw new InternalError(e.toString(), e);
        } catch (InvocationTargetException e) {
            Throwable t = e.getCause();
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new InternalError(t.toString(), t);
            }
        } catch (NoSuchMethodException e) {
            throw new InternalError(e.toString(), e);
        }
    }

有一个弱引用的实例map 每次去拿 但是因为是弱引用可能被GC回收，所以比较耗时。

2.cglib动态代理

生成一个子类继承要代理的类，并重写所有方法

3.spring代理

package com.hyq.btc.cos.filter;


import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @author dibulidohu
 * @classname Aop
 * @date 2019/2/1419:45
 * @description
 */
@Aspect
@Component
public class Aop {

    @Pointcut(value = "execution(* com.hyq.btc.cos.service.IEinvoiceService.*(..))")
    public void aop(){}

    @Before(value = "aop()")
    public void before(JoinPoint joinPoint) {
        System.out.println("Logging before " + joinPoint.getSignature().getName());
    }

    @After("aop()")
    public void after(JoinPoint joinPoint) {
        System.out.println("Logging after " + joinPoint.getSignature().getName());
    }

    @Around("aop()")
    public Object aroud(ProceedingJoinPoint joinpoint) throws Throwable {
        System.out.println("Logging around before" + joinpoint.getSignature().getName());
        joinpoint.proceed();
        System.out.println("Logging around after" + joinpoint.getSignature().getName());
        return null;
    }

    @AfterThrowing("aop()")
    public void afterthr(JoinPoint joinPoint) {
        System.out.println("Logging after throw " + joinPoint.getSignature().getName());
    }
}