JdkDynamicAopProxy-笔记

Posted 2020-10-20 渔翁

这个接口的继承体系图：

 一、AopProxy

InvocationHandler就不说了，看看AopProxy的源码。

/**
 * Delegate interface for a configured AOP proxy, allowing for the creation
 * of actual proxy objects.
 *
 * <p>Out-of-the-box implementations are available for JDK dynamic proxies
 * and for CGLIB proxies, as applied by {@link DefaultAopProxyFactory}.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see DefaultAopProxyFactory
 */
public interface AopProxy {

    /**创建一个代理对象。（为目标对象创建一个代理对象。）
     * Create a new proxy object.
     * <p>Uses the AopProxy\'s default class loader (if necessary for proxy creation):
     * usually, the thread context class loader.
     * @return the new proxy object (never {@code null})
     * @see Thread#getContextClassLoader()
     */
    Object getProxy();

    /**重载方法。上面的无参方法会调用这个重载方法。
     * Create a new proxy object.
     * <p>Uses the given class loader (if necessary for proxy creation).
     * {@code null} will simply be passed down and thus lead to the low-level
     * proxy facility\'s default, which is usually different from the default chosen
     * by the AopProxy implementation\'s {@link #getProxy()} method.
     * @param classLoader the class loader to create the proxy with
     * (or {@code null} for the low-level proxy facility\'s default)
     * @return the new proxy object (never {@code null})
     */
    Object getProxy(ClassLoader classLoader);

}

 二、JdkDynamicAopProxy

 

/**
 * JDK-based {@link AopProxy} implementation for the Spring AOP framework,
 * based on JDK {@link java.lang.reflect.Proxy dynamic proxies}.
 *
 * <p>Creates a dynamic proxy, implementing the interfaces exposed by
 * the AopProxy. Dynamic proxies <i>cannot</i> be used to proxy methods
 * defined in classes, rather than interfaces.
 *
 * <p>Objects of this type should be obtained through proxy factories,
 * configured by an {@link AdvisedSupport} class. This class is internal
 * to Spring\'s AOP framework and need not be used directly by client code.
 *
 * <p>Proxies created using this class will be thread-safe if the
 * underlying (target) class is thread-safe.
 *
 * <p>Proxies are serializable so long as all Advisors (including Advices
 * and Pointcuts) and the TargetSource are serializable.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Dave Syer
 * @see java.lang.reflect.Proxy
 * @see AdvisedSupport
 * @see ProxyFactory
 */
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {

    /** use serialVersionUID from Spring 1.2 for interoperability */
    private static final long serialVersionUID = 5531744639992436476L;


    /*
     * NOTE: We could avoid the code duplication between this class and the CGLIB
     * proxies by refactoring "invoke" into a template method. However, this approach
     * adds at least 10% performance overhead versus a copy-paste solution, so we sacrifice
     * elegance for performance. (We have a good test suite to ensure that the different
     * proxies behave the same :-)
     * This way, we can also more easily take advantage of minor optimizations in each class.
     */

    /** We use a static Log to avoid serialization issues */
    private static final Log logger = LogFactory.getLog(JdkDynamicAopProxy.class);

    /** Config used to configure this proxy */
    private final AdvisedSupport advised;

    /**
     * Is the {@link #equals} method defined on the proxied interfaces?
     */
    private boolean equalsDefined;

    /**
     * Is the {@link #hashCode} method defined on the proxied interfaces?
     */
    private boolean hashCodeDefined;


    /**
     * Construct a new JdkDynamicAopProxy for the given AOP configuration.
     * @param config the AOP configuration as AdvisedSupport object
     * @throws AopConfigException if the config is invalid. We try to throw an informative
     * exception in this case, rather than let a mysterious failure happen later.
     */
    public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
        Assert.notNull(config, "AdvisedSupport must not be null");
        if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
            throw new AopConfigException("No advisors and no TargetSource specified");
        }
        this.advised = config;
    }


    @Override
    public Object getProxy() {
        return getProxy(ClassUtils.getDefaultClassLoader());
    }

    @Override
    public Object getProxy(ClassLoader classLoader) {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
        }
　　　　　//代理接口。代理对象的接口，通常包括目标对象的实现的接口、Advised接口、SpringProxy接口
        Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
        findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
        return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);//返回代理对象。
    }

    /**
     * Finds any {@link #equals} or {@link #hashCode} method that may be defined
     * on the supplied set of interfaces.
     * @param proxiedInterfaces the interfaces to introspect
     */
    private void findDefinedEqualsAndHashCodeMethods(Class<?>[] proxiedInterfaces) {
        for (Class<?> proxiedInterface : proxiedInterfaces) {
            Method[] methods = proxiedInterface.getDeclaredMethods();
            for (Method method : methods) {
                if (AopUtils.isEqualsMethod(method)) {
                    this.equalsDefined = true;
                }
                if (AopUtils.isHashCodeMethod(method)) {
                    this.hashCodeDefined = true;
                }
                if (this.equalsDefined && this.hashCodeDefined) {
                    return;
                }
            }
        }
    }


    /**
     * 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 {
            
            //是否重写了euquals方法，并且当前调用的方法就是的equals方法.
            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.
                //是否重写了hashCode方法并且当前调用的是hashCode方法。
                return hashCode();
            }
            else if (method.getDeclaringClass() == DecoratingProxy.class) {
                // There is only getDecoratedClass() declared -> dispatch to proxy config.
                return AopProxyUtils.ultimateTargetClass(this.advised);
            }
            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;

            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.
            //尽量晚点获取目标对象。
            target = targetSource.getTarget();
            if (target != null) {
                targetClass = target.getClass();
            }

            // Get the interception chain for this method.获取目标方法对应的拦截器链
            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()) {//如果拦截器链为空，那么直接调用目标对象。
                // 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.
                //拦截器链为空的话就不需要创建MethodInvocation对象（连接点）了,直接调用目标对象。
                Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
                retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
            }
            else {
                // We need to create a method invocation...
                //拦截器链不为空，创建一个调用
                invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
                // Proceed to the joinpoint through the interceptor chain.
                //开始调用拦截器链和目标方法.
                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);
            }
        }
    }


    /**
     * Equality means interfaces, advisors and TargetSource are equal.
     * <p>The compared object may be a JdkDynamicAopProxy instance itself
     * or a dynamic proxy wrapping a JdkDynamicAopProxy instance.
     */
    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if (other == null) {
            return false;
        }

        JdkDynamicAopProxy otherProxy;
        if (other instanceof JdkDynamicAopProxy) {
            otherProxy = (JdkDynamicAopProxy) other;
        }
        else if (Proxy.isProxyClass(other.getClass())) {
            InvocationHandler ih = Proxy.getInvocationHandler(other);
            if (!(ih instanceof JdkDynamicAopProxy)) {
                return false;
            }
            otherProxy = (JdkDynamicAopProxy) ih;
        }
        else {
            // Not a valid comparison...
            return false;
        }

        // If we get here, otherProxy is the other AopProxy.
        return AopProxyUtils.equalsInProxy(this.advised, otherProxy.advised);
    }

    /**
     * Proxy uses the hash code of the TargetSource.
     */
    @Override
    public int hashCode() {
        return JdkDynamicAopProxy.class.hashCode() * 13 + this.advised.getTargetSource().hashCode();
    }

}