Spring Aop之JDK方式创建代理类的源码思路

Posted 2023-02-02 javartisan

import org.aopalliance.intercept.MethodInvocation;
import org.aopalliance.intercept.MethodInterceptor;

public class CustomMethodAdvice implements MethodInterceptor 

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable 
        System.out.println("CustomMethodInterceptor  Before !");
        Object an = invocation.proceed();
        System.out.println("CustomMethodInterceptor  After !");
        return an;
    

 

测试代码：

    @Test
    public void testProxyFactory() 

        ProxyFactory proxyFactory = new ProxyFactory();

        proxyFactory.setTarget(new UserServiceImpl());

        // 不设置接口的话使用CGLIB
        proxyFactory.setInterfaces(UserService.class);

        // 不指定Pointcut的话，默认是TrueMethodMatcher，即匹配所有方法
        proxyFactory.addAdvice(new CustomMethodAdvice());

        UserService us = (UserService) proxyFactory.getProxy();

        System.out.println(us.login("daxin"));

        saveClassFile(us.getClass(), "UserServiceProxy");

        DecoratingProxy dp = (DecoratingProxy) us;
        System.out.println(dp.getDecoratedClass());
    

 

Jdk生成的代理类继承结构：

 

接口作用：

UserService：目标对象的接口，用于生成相应类型的代理类。
SpringProxy：Spring代理类的标记接口，用于Spring内部判断对象是否是Spring代理
Advised：Spring Aop配置信息的持有对象
DecoratingProxy：用于获取目标对象的真是Class名字

 

生成代理对象的方法org.springframework.aop.framework.JdkDynamicAopProxy#getProxy(java.lang.ClassLoader)：

@Override
public Object getProxy(ClassLoader classLoader) 
	// 根据advised信息获取代理类需要实现的接口，同时三个：SpringProxy，Advised以及目标对象接口
	Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
	// 校验是否自定义实现了equals与hashCode方法
	findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
	//生成代理类，this对象包含了整个Aop的配置信息
	return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);

当代理对象进行方法调用时候会触发org.springframework.aop.framework.JdkDynamicAopProxy#invoke方法：

	/**
	 * Implementation of @code InvocationHandler.invoke.
	 * <p>Callers will see exactly the exception thrown by the target,
	 * unless a hook method throws an exception.
	 */
	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable 
		MethodInvocation invocation;
		Object oldProxy = null;
		boolean setProxyContext = false;

		TargetSource targetSource = this.advised.targetSource;
		Class<?> targetClass = null;
		Object target = null;

		try 

			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) 
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			
			if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) 
				// The target does not implement the hashCode() method itself.
				return hashCode();
			

			// 由于代理类实现了： 目标对象接口, SpringProxy, Advised, DecoratingProxy等接口，因此方法调用时候必须按照类型进行特殊处理

			//1：Advised类型处理
			if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
					method.getDeclaringClass().isAssignableFrom(Advised.class)) 
				// Service invocations on ProxyConfig with the proxy config...
				return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
			

			Object retVal;

			if (this.advised.exposeProxy) 
				// Make invocation available if necessary.
				oldProxy = AopContext.setCurrentProxy(proxy);
				setProxyContext = true;
			

			// May be null. Get as late as possible to minimize the time we "own" the target,
			// in case it comes from a pool.
			target = targetSource.getTarget();
			if (target != null) 
				targetClass = target.getClass();
			

			// Get the interception chain for this method.
			List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

			// Check whether we have any advice. If we don't, we can fallback on direct
			// reflective invocation of the target, and avoid creating a MethodInvocation.
			if (chain.isEmpty()) 
				// We can skip creating a MethodInvocation: just invoke the target directly
				// Note that the final invoker must be an InvokerInterceptor so we know it does
				// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
				Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
			
			else 
				// We need to create a method invocation...
				invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				retVal = invocation.proceed();
			

			// Massage return value if necessary.
			Class<?> returnType = method.getReturnType();
			if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
					!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) 
				// Special case: it returned "this" and the return type of the method
				// is type-compatible. Note that we can't help if the target sets
				// a reference to itself in another returned object.
				retVal = proxy;
			
			else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) 
				throw new AopInvocationException(
						"Null return value from advice does not match primitive return type for: " + method);
			
			return retVal;
		
		finally 
			if (target != null && !targetSource.isStatic()) 
				// Must have come from TargetSource.
				targetSource.releaseTarget(target);
			
			if (setProxyContext) 
				// Restore old proxy.
				AopContext.setCurrentProxy(oldProxy);
			
		
	



	/**
	 * Implementation of @code InvocationHandler.invoke.
	 * <p>Callers will see exactly the exception thrown by the target,
	 * unless a hook method throws an exception.
	 */
	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable 
		MethodInvocation invocation;
		Object oldProxy = null;
		boolean setProxyContext = false;

		TargetSource targetSource = this.advised.targetSource;
		Class<?> targetClass = null;
		Object target = null;

		try 

			// equals与hashCode方法调用处理
			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) 
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			
			else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) 
				// The target does not implement the hashCode() method itself.
				return hashCode();
			
			// 由于代理类实现了： 目标对象接口, SpringProxy, Advised, DecoratingProxy等接口，因此方法调用时候必须按照类型进行特殊处理

			//1：DecoratingProxy类型方法调用
			else if (method.getDeclaringClass() == DecoratingProxy.class) 
				// There is only getDecoratedClass() declared -> dispatch to proxy config.
				return AopProxyUtils.ultimateTargetClass(this.advised);
			

			// 2:Advised类型方法调用
			else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
					method.getDeclaringClass().isAssignableFrom(Advised.class)) 
				// Service invocations on ProxyConfig with the proxy config...
				return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
			

			Object retVal;
			//是否开启对象设置到当前上下文中，开启的话可以进行设置
			if (this.advised.exposeProxy) 
				// Make invocation available if necessary.
				oldProxy = AopContext.setCurrentProxy(proxy);
				setProxyContext = true;
			

			// 代理对象的目标方法调用处理
			// May be null. Get as late as possible to minimize the time we "own" the target,
			// in case it comes from a pool.
			target = targetSource.getTarget();
			if (target != null) 
				targetClass = target.getClass();
			

			// Get the interception chain for this method.
			// 获取当前方法的增强逻辑,根据的是MethodMatcher组件为依据
			List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

			// Check whether we have any advice. If we don't, we can fallback on direct
			// reflective invocation of the target, and avoid creating a MethodInvocation.
			//没有增强逻辑则直接进行目标方法调用
			if (chain.isEmpty()) 
				// We can skip creating a MethodInvocation: just invoke the target directly
				// Note that the final invoker must be an InvokerInterceptor so we know it does
				// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
				Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
			
			else 
				// We need to create a method invocation...
				// 将调用信息封装成MethodInvocation信息，然后进行反射调用
				invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				retVal = invocation.proceed();
			

			// Massage return value if necessary.
			Class<?> returnType = method.getReturnType();
			if (retVal != null && retVal == target &&
					returnType != Object.class && returnType.isInstance(proxy) &&
					!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) 
				// Special case: it returned "this" and the return type of the method
				// is type-compatible. Note that we can't help if the target sets
				// a reference to itself in another returned object.
				retVal = proxy;
			
			else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) 
				throw new AopInvocationException(
						"Null return value from advice does not match primitive return type for: " + method);
			
			return retVal;
		
		finally 
			if (target != null && !targetSource.isStatic()) 
				// Must have come from TargetSource.
				targetSource.releaseTarget(target);
			
			if (setProxyContext) 
				// Restore old proxy.
				AopContext.setCurrentProxy(oldProxy);
			
		
	

到此就完成了方法的调用。