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Spring Core动态代理的实现代码

2022-02-22 13:02大头河 Java教程

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，接下来通过本文给大家介绍Spring Core动态代理的相关知识,需要的朋友可以参考下

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;
    }
 
}

到此这篇关于Spring Core动态代理的文章就介绍到这了,更多相关Spring Core动态代理内容请搜索服务器之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持服务器之家！

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

  • core
  • spring
  • 动态代理

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