Spring Core动态代理的实现代码

时间：2021-11-13 22:48:02

1.设计原理

通过JDK的Proxy方式或者CGLIB方式生成代理对象的时候，相关的拦截器已经配置到代理对象中去了；
通过拦截器回调

JDK动态代理：代理类和目标类实现了共同的接口，用到InvocationHandler接口。(见下面代码)
CGLIB动态代理：代理类是目标类的子类，用到MethodInterceptor接口。(见下面代码)

jdk动态代理是由Java内部的反射机制来实现的；
cglib动态代理底层则是借助asm来实现的。

jdk （Proxy）

使用了Proxy类的newProxyInstance()方法来创建代理对象

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final UserService target=new UserServiceImpl();
Class<UserService> clazz = UserService.class;
ClassLoader loader = clazz.getClassLoader();
Object proxyInstance = Proxy.newProxyInstance(loader, new Class[]{clazz}, new InvocationHandler() {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Before...");
        Object result = method.invoke(target, args);
        System.out.println("After...");
        return result;
    }
});
UserService service = (UserService) proxyInstance;
service.getUserInfo();

cglib

动态类对象Enhancer，它是CGLIB的核心类；Enhancer类的setSuperclass()方法来确定目标对象；setCallback()方法添加回调函数。最后通过return 语句将创建的代理类对象返回。intercept()方法会在程序执行目标方法时被调用，方法运行时会执行切面类中的增强方法（前和后）。

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Enhancer enhancer=new Enhancer();
enhancer.setSuperclass(UserInfo.class);
enhancer.setCallbacks(new Callback[]{new MethodInterceptor() {
    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("Before...");
        Object result = methodProxy.invokeSuper(o, objects);
        System.out.println("After...");
        return result;
    }
}});
 
UserInfo userInfo = (UserInfo) enhancer.create();
userInfo.test();

2.ProxyFactory (Spring-Core)

ProxyFactory在生成代理对象之前需要决定到底是使用JDK动态代理还是CGLIB技术；
getProxy() 返回 CglibAopProxy 或者 JdkDynamicAopProxy

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        UserService target=new UserServiceImpl();
 
        ProxyFactory proxyFactory=new ProxyFactory();
        proxyFactory.setTarget(target);
 
        //addAdvice() 添加多个，自动形成责任链
        proxyFactory.addAdvice(new AopMethodAroundAdvice());
        proxyFactory.addAdvice(new AopMethodBeforeAdvice());
        proxyFactory.addAdvice(new AopMethodAfterAdvice());
        proxyFactory.addAdvice(new AopMethodThrowsAdvice());
        
        //Advisor 设置具体 pointCut和  advice
//        proxyFactory.addAdvisor(new AopPointcutAdvisor());
 
        UserService userService = (UserService) proxyFactory.getProxy();
        userService.getUserInfo();
        userService.test();
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public Object getProxy() {
        return createAopProxy().getProxy();
    }

2.1 JdkDynamicAopProxy

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final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
 
    @Override
    public Object getProxy() {
        return getProxy(ClassUtils.getDefaultClassLoader());
    }
 
    @Override
    public Object getProxy(@Nullable ClassLoader classLoader) {
        if (logger.isTraceEnabled()) {
            logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
        }
        return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
    }
    @Override
    @Nullable
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            
            ...省略...
            Object retVal;
 
            if (this.advised.exposeProxy) {
                // Make invocation available if necessary.
                oldProxy = AopContext.setCurrentProxy(proxy);
                setProxyContext = true;
            }
 
            // Get as late as possible to minimize the time we "own" the target,
            // in case it comes from a pool.
            target = targetSource.getTarget();
            Class<?> targetClass = (target != null ? target.getClass() : null);
 
            //重点：获取此方法的拦截链
            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...
                MethodInvocation 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);
            }
        }
    }

2.2 CglibAopProxy

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class CglibAopProxy implements AopProxy, Serializable {
 
    @Override
    public Object getProxy() {
        return getProxy(null);
    }
 
    @Override
    public Object getProxy(@Nullable ClassLoader classLoader) {
        if (logger.isTraceEnabled()) {
            logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());
        }
 
        try {
            Class<?> rootClass = this.advised.getTargetClass();
            Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
 
            Class<?> proxySuperClass = rootClass;
            if (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {
                proxySuperClass = rootClass.getSuperclass();
                Class<?>[] additionalInterfaces = rootClass.getInterfaces();
                for (Class<?> additionalInterface : additionalInterfaces) {
                    this.advised.addInterface(additionalInterface);
                }
            }
 
            // Validate the class, writing log messages as necessary.
            validateClassIfNecessary(proxySuperClass, classLoader);
 
            // Configure CGLIB Enhancer...
            Enhancer enhancer = createEnhancer();
            if (classLoader != null) {
                enhancer.setClassLoader(classLoader);
                if (classLoader instanceof SmartClassLoader &&
                        ((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
                    enhancer.setUseCache(false);
                }
            }
            enhancer.setSuperclass(proxySuperClass);
            enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
            enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
            enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));
 
            //重点：设置Callbacks[]
            Callback[] callbacks = getCallbacks(rootClass);
            Class<?>[] types = new Class<?>[callbacks.length];
            for (int x = 0; x < types.length; x++) {
                types[x] = callbacks[x].getClass();
            }
            // fixedInterceptorMap only populated at this point, after getCallbacks call above
            enhancer.setCallbackFilter(new ProxyCallbackFilter(
                    this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
            enhancer.setCallbackTypes(types);
 
            // Generate the proxy class and create a proxy instance.
            return createProxyClassAndInstance(enhancer, callbacks);
        }
        catch (CodeGenerationException | IllegalArgumentException ex) {
            throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
                    ": Common causes of this problem include using a final class or a non-visible class",
                    ex);
        }
        catch (Throwable ex) {
            // TargetSource.getTarget() failed
            throw new AopConfigException("Unexpected AOP exception", ex);
        }
    }
 
    //获取Callbacks[]
    private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
        // Parameters used for optimization choices...
        boolean exposeProxy = this.advised.isExposeProxy();
        boolean isFrozen = this.advised.isFrozen();
        boolean isStatic = this.advised.getTargetSource().isStatic();
 
        // Choose an "aop" interceptor (used for AOP calls). (重要类)
        Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
 
        // Choose a "straight to target" interceptor. (used for calls that are
        // unadvised but can return this). May be required to expose the proxy.
        Callback targetInterceptor;
        if (exposeProxy) {
            targetInterceptor = (isStatic ?
                    new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
                    new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource()));
        }
        else {
            targetInterceptor = (isStatic ?
                    new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
                    new DynamicUnadvisedInterceptor(this.advised.getTargetSource()));
        }
 
        // Choose a "direct to target" dispatcher (used for
        // unadvised calls to static targets that cannot return this).
        Callback targetDispatcher = (isStatic ?
                new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp());
 
        Callback[] mainCallbacks = new Callback[] {
                aopInterceptor,  // for normal advice
                targetInterceptor,  // invoke target without considering advice, if optimized
                new SerializableNoOp(),  // no override for methods mapped to this
                targetDispatcher, this.advisedDispatcher,
                new EqualsInterceptor(this.advised),
                new HashCodeInterceptor(this.advised)
        };
 
        Callback[] callbacks;
        ...省略...
        return callbacks;
    }

DynamicAdvisedInterceptor

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private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
 
    private final AdvisedSupport advised;
 
    public DynamicAdvisedInterceptor(AdvisedSupport advised) {
        this.advised = advised;
    }
 
    @Override
    @Nullable
    public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        Object oldProxy = null;
        boolean setProxyContext = false;
        Object target = null;
        TargetSource targetSource = this.advised.getTargetSource();
        try {
            if (this.advised.exposeProxy) {
                // Make invocation available if necessary.
                oldProxy = AopContext.setCurrentProxy(proxy);
                setProxyContext = true;
            }
            // Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
            target = targetSource.getTarget();
            Class<?> targetClass = (target != null ? target.getClass() : null);
            //重点：获取此方法的拦截链
            List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
            Object retVal;
            // Check whether we only have one InvokerInterceptor: that is,
            // no real advice, but just reflective invocation of the target.
            if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
                // 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 = methodProxy.invoke(target, argsToUse);
            }
            else {
                // We need to create a method invocation...
                retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
            }
            retVal = processReturnType(proxy, target, method, retVal);
            return retVal;
        }
        finally {
            if (target != null && !targetSource.isStatic()) {
                targetSource.releaseTarget(target);
            }
            if (setProxyContext) {
                // Restore old proxy.
                AopContext.setCurrentProxy(oldProxy);
            }
        }
    }
}

2.3 主要源码部分

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public class AdvisedSupport extends ProxyConfig implements Advised {
 
    public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable Class<?> targetClass) {
        MethodCacheKey cacheKey = new MethodCacheKey(method);
        List<Object> cached = this.methodCache.get(cacheKey);
        if (cached == null) {
            cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
                    this, method, targetClass);
            this.methodCache.put(cacheKey, cached);
        }
        return cached;
    }

DefaultAdvisorChainFactory

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public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable {
 
    @Override
    public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
            Advised config, Method method, @Nullable Class<?> targetClass) {
 
        // This is somewhat tricky... We have to process introductions first,
        // but we need to preserve order in the ultimate list.
        AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
        Advisor[] advisors = config.getAdvisors();
        List<Object> interceptorList = new ArrayList<>(advisors.length);
        Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
        Boolean hasIntroductions = null;
 
        for (Advisor advisor : advisors) {
            if (advisor instanceof PointcutAdvisor) {
                // Add it conditionally.
                PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
                if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
                    MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
                    boolean match;
                    if (mm instanceof IntroductionAwareMethodMatcher) {
                        if (hasIntroductions == null) {
                            hasIntroductions = hasMatchingIntroductions(advisors, actualClass);
                        }
                        match = ((IntroductionAwareMethodMatcher) mm).matches(method, actualClass, hasIntroductions);
                    }
                    else {
                        match = mm.matches(method, actualClass);
                    }
                    if (match) {
                    //重点：将advisor中的advice转换为MethodInterceptor。
                        MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
                        if (mm.isRuntime()) {
                            // Creating a new object instance in the getInterceptors() method
                            // isn't a problem as we normally cache created chains.
                            for (MethodInterceptor interceptor : interceptors) {
                                interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
                            }
                        }
                        else {
                            interceptorList.addAll(Arrays.asList(interceptors));
                        }
                    }
                }
            }
            else if (advisor instanceof IntroductionAdvisor) {
                IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
                if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
                    Interceptor[] interceptors = registry.getInterceptors(advisor);
                    interceptorList.addAll(Arrays.asList(interceptors));
                }
            }
            else {
                Interceptor[] interceptors = registry.getInterceptors(advisor);
                interceptorList.addAll(Arrays.asList(interceptors));
            }
        }
 
        return interceptorList;
    }

DefaultAdvisorAdapterRegistry

构造方法注册了 MethodBeforeAdviceAdapter、AfterReturningAdviceAdapter、ThrowsAdviceAdapter 3个Adapter模板
通过getInterceptors(Advisor advisor) 方法，将 Advisor 总的advice 转换成 MethodInterceptor

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public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {
 
    private final List<AdvisorAdapter> adapters = new ArrayList<>(3);
 
 
    /**
     * Create a new DefaultAdvisorAdapterRegistry, registering well-known adapters.
     */
    public DefaultAdvisorAdapterRegistry() {
        registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
        registerAdvisorAdapter(new AfterReturningAdviceAdapter());
        registerAdvisorAdapter(new ThrowsAdviceAdapter());
    }
 
...省略...
    @Override
    public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
        List<MethodInterceptor> interceptors = new ArrayList<>(3);
        Advice advice = advisor.getAdvice();
        if (advice instanceof MethodInterceptor) {
            interceptors.add((MethodInterceptor) advice);
        }
        for (AdvisorAdapter adapter : this.adapters) {
            if (adapter.supportsAdvice(advice)) {
                interceptors.add(adapter.getInterceptor(advisor));
            }
        }
        if (interceptors.isEmpty()) {
            throw new UnknownAdviceTypeException(advisor.getAdvice());
        }
        return interceptors.toArray(new MethodInterceptor[0]);
    }
 
    @Override
    public void registerAdvisorAdapter(AdvisorAdapter adapter) {
        this.adapters.add(adapter);
    }
 
}

1.AfterReturningAdviceAdapter 通过getInterceptor方法 获取 AfterReturningAdviceInterceptor 过滤器
2. AfterReturningAdviceInterceptor invoke()方法 先执行目标方法，后执行（后置）advice了方法

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class AfterReturningAdviceAdapter implements AdvisorAdapter, Serializable {
 
    @Override
    public boolean supportsAdvice(Advice advice) {
        return (advice instanceof AfterReturningAdvice);
    }
 
    @Override
    public MethodInterceptor getInterceptor(Advisor advisor) {
        AfterReturningAdvice advice = (AfterReturningAdvice) advisor.getAdvice();
        return new AfterReturningAdviceInterceptor(advice);
    }
 
}
 
public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {
 
    private final AfterReturningAdvice advice;
 
 
    /**
     * Create a new AfterReturningAdviceInterceptor for the given advice.
     * @param advice the AfterReturningAdvice to wrap
     */
    public AfterReturningAdviceInterceptor(AfterReturningAdvice advice) {
        Assert.notNull(advice, "Advice must not be null");
        this.advice = advice;
    }
 
 
    @Override
    @Nullable
    public Object invoke(MethodInvocation mi) throws Throwable {
        Object retVal = mi.proceed();
        this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
        return retVal;
    }
 
}

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原文链接：https://blog.csdn.net/qq_18398239/article/details/120822558

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