【JavaEE进阶】Spring AOP 原理

在之前的博客中 【JavaEE进阶】Spring AOP使用篇_aop多个切点-CSDN博客

我们主要学习了SpringAOP的应用, 接下来我们来学习SpringAOP的原理, 也就是Spring是如何实现AOP的.

SpringAOP 是基于动态代理来实现AOP的,咱们学习内容主要分以下两部分

1.代理模式

2.Spring AOP源码剖析

1.代理模式

定义: 为其他对象提供一种代理以控制对这个对象的访问, 它的作用就是通过提供一个代理类, 让我们在调用目标方法的时候, 不再是直接对目标方法进行调用, 而是通过代理类间接调用.

在某些情况下, 一个对象不适合或者不能直接引用另一个对象, 而代理对象可以在客户端和目标对象之间起到中介的作用.

使用代理前:

使用代码后:

比如房屋租赁:

Subject: 就是提前定义了房东做的事情,交给中介代理,也是中介要做的事情

RealSubiect: 房东

Proxy: 中介

UML 类图如下:

代理模式可以在不修改被代理对象的基础上, 通过扩展代理类, 进行一些功能的附加与增强

根据代理的创建时期, 代理模式分为静态代理 和动态代理:

静态代理: 由程序员创建代理类或特定工具自动生成源代码再对其编译,在程序运行前代理类的

class 文件就已经存在了

动态代理: 在程序运行时,运用反射机制动态创建而成

静态代理: 由程序员创建代理类或特定工具自动生成源代码再对其编译, 在程序运行前代理类的.class 文件就已经存在了
动态代理: 在程序运行时, 运用反射机制动态创建而成

以房东和中介的的关系举例:

1.1 静态代理

以房东和中介的例子模拟静态代理:

1.定义接口(定义房东要做的事情,也是中介需要做的事情)

package com.example.aop.proxy;

/**
 * 业务接口类
 */
public interface HouseSubject {
    void rentHouse();

    void saleHouse();
}

2.实现接口(房东出租房子)目标对象:

package com.example.aop.proxy;


/**
 * 业务实现类
 */
public class RealHouseSubject implements HouseSubject {

    @Override
    public void rentHouse() {
        System.out.println("我是房东, 我出租房子");
    }

    @Override
    public void saleHouse() {
        System.out.println("我是房东, 我出售房子");
    }
}

3.代理(中介,帮房东出租房子)

package com.example.aop.proxy;


/**
 * 静态代理的代理类 (中介)
 */

public class HouseProxy implements HouseSubject {

    //房东对象
    private HouseSubject target;

    public HouseProxy(HouseSubject target) {
        this.target = target;
    }

    @Override
    public void rentHouse() {
        //代理前
        System.out.println("我是中介, 开始代理");
        //出租房子
        target.rentHouse();
        //出租后
        System.out.println("我是中介, 结束代理");
    }

    @Override
    public void saleHouse() {
        //代理前
        System.out.println("我是中介, 开始代理");
        //出售房子
        target.saleHouse();
        //出租后
        System.out.println("我是中介, 结束代理");
    }
}

测试:

package com.example.aop.proxy;

public class Main {
    public static void main(String[] args) {
//        静态代理
        HouseProxy proxy = new HouseProxy(new RealHouseSubject());
        proxy.rentHouse();
        proxy.saleHouse();
        System.out.println("========================");
        HouseSubject houseSubject = new RealHouseSubject();
        houseSubject.rentHouse();
        houseSubject.saleHouse();
    }
}

上面这个代理实现方式就是静态代理(仿佛啥也没干).

从上述程序可以看出, 虽然静态代理也完成了对目标对象的代理, 但是由于代码都写死了, 对目标对象的每个方法的增强都是手动完成的，非常不灵活. 所以日常开发几乎看不到静态代理的场景.

我们修改接口(Subject)和业务实现类(RealSubject)时, 还需要修改代理类(Proxy).

同样的, 如果有新增接口(Subiect)和业务实现类(RealSubiect), 也需要对每一个业务实现类新增代理类(Proxy). 既然代理的流程是一样的, 有没有一种办法, 让他们通过一个代理类来实现呢?

这就需要用到动态代理技术了

1.2 动态代理

相比于静态代理来说，动态代理更加灵活.

我们不需要针对每个目标对象都单独创建一个代理对象, 而是把这个创建代理对象的工作推迟到程序运行时由JVM来实现, 也就是说动态代理在程序运行时, 根据需要动态创建生成

比如房屋中介,我不需要提前预测都有哪些业务, 而是业务来了我再根据情况创建

我们还是先看代码再来理解，Java也对动态代理进行了实现, 并给我们提供了一些AP1, 常见的实现方式有两种:

动态代理在我们日常开发中使用的相对较少，但是在框架中几乎是必用的一门技术, 学会了动态代理之后, 对于我们理解和学习各种框架的原理也非常有帮助.

JDK动态代理

JDK动态代理实现步骤:

定义JDK动态代理类

实现 InvocationHandler 接口

package com.example.aop.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class JDKInvocationHandler implements InvocationHandler   {
    private Object target; //目标对象

    public JDKInvocationHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("我是代理, 开始代理");
        //通过反射, 调用目标对象的方法
        Object result = method.invoke(target, args);
        System.out.println("我是代理, 结束代理");
        return result;
    }
}

创建一个代理对象并使用:

import java.lang.reflect.Proxy;

public class Main {
    public static void main(String[] args) {
        //JDK动态代理
        /**
         *     public static Object newProxyInstance(ClassLoader loader,
         *                                           Class<?>[] interfaces,
         *                                           InvocationHandler h) {
         *     loader: 加载我们代理类的classload
         *     interfaces: 要实现的接口
         *     h: 代理要做的事情, 需要实现 InvocationHandler 这个接口
         */
        //目标对象
        RealHouseSubject target = new RealHouseSubject();
        //动态生成代理对象
        HouseSubject proxy = (HouseSubject) Proxy.newProxyInstance(target.getClass().getClassLoader(),
                    new Class[] {HouseSubject.class},
                    new JDKInvocationHandler(target));
        proxy.rentHouse();
        proxy.saleHouse();
    }
}

JDK动态代理只能代理接口, 不能代理类:

运行成功

运行失败

CGLIB动态代理

JDK 动态代理有一个最致命的问题是其只能代理实现了接口的类

有些场景下,我们的业务代码是直接实现的,并没有接口定义,为了解决这个问题,我们可以用 CGLIB 动态代理机制来解决.

CGLIB(Code Generation Library)是一个基于ASM的字节码生成库，它允许我们在运行时对字节码进行修改和动态生成. CGLIB 通过继承方式实现代理，很多知名的开源框架都使用到了CGLIB.

例如 Spring中的 AOP 模块中: 如果目标对象实现了接口，则默认采用 JDK动态代理, 否则采用 CGLIB 动态代理.

CGLIB 动态代理类实现步骤

添加依赖

和JDK动态代理不同, CGLlB(Code Generation Library) 实际是属于一个开源项目，如果你要使用它的话，需要手动添加相关依赖

<dependency>
 <groupId>cglib</groupId>
 <artifactId>cglib</artifactId>
 <version>3.3.0</version>
</dependency>

自定义 MethodInterceptor(方法拦截器)

实现MethodInterceptor接

package com.example.aop.proxy;

import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

public class CGLibMethodInterceptor implements MethodInterceptor {

    private Object target;

    public CGLibMethodInterceptor(Object target) {
        this.target = target;
    }

    /**
     * 调用代理对象
     */
    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("我是中介, 开始代理");
        Object result = method.invoke(target, args);
        System.out.println("我是中介, 结束代理");
        return result;
    }
}

创建代理类,并使用

package com.example.aop.proxy;

import org.springframework.cglib.proxy.Enhancer;

public class Main {
    public static void main(String[] args) {
        //使用CGLib完成代理

        //代理接口, 运行成功
        HouseSubject target = new RealHouseSubject();
        HouseSubject houseSubject = (HouseSubject) Enhancer.create(target.getClass(), new CGLibMethodInterceptor(target));
        houseSubject.saleHouse();
        houseSubject.rentHouse();
        System.out.println("====================");
        //代理类, 运行成功
        RealHouseSubject realHouseSubject =  (RealHouseSubject) Enhancer.create(target.getClass(), new CGLibMethodInterceptor(target));
        realHouseSubject.saleHouse();
        realHouseSubject.rentHouse();
    }
}

CGLIB既可以代理接口, 又可以代理类:

代码简单讲解
1. Methodinterceptor

MethodInterceptor 和 JDK动态代理中的 InvocationHandler 类似，它只定义了一个方法 intercept(),用于增强目标方法,

public interface MethodInterceptor extends Callback {
 /**
 * 参数说明: 
 * o: 被代理的对象 
 * method: ⽬标⽅法(被拦截的⽅法, 也就是需要增强的⽅法) 
 * objects: ⽅法⼊参 
 * methodProxy: ⽤于调⽤原始⽅法 
 */
 Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable;
}

2. Enhancer.create()

Enhancer.create()用来生成一个代理对象

public static Object create(Class type, Callback callback) {
 //...代码省略 
}

参数说明:

type: 被代理类的类型(类或接口)

callback: 自定义方法拦截器 MethodInterceptor

JDK动态代理和CGLIB动态代理的区别

JDK 可以代理接口, 不可以代理类

CGLib 既可以代理接口, 又可以代理类

JDK 动态代理是 Java 标准库的一部分，不需要额外的依赖。只要使用的是 Java 开发环境，就可以直接使用 JDK 动态代理

CGLIB 是一个第三方库，需要在项目中添加相应的依赖才能使用。

2. SpringAOP 源码阅读

SpringAOP 主要基于两种方式实现的: JDK及 CGLIB 的方式

生成代理对象的逻辑在父类 AbstractAutoProxyCreator 中

Spring 对于 AOP 的实现，基本上都是靠 AnnotationAwareAspectJAutoProxyCreator 去完成

/**
 * {@link org.springframework.beans.factory.config.BeanPostProcessor} implementation
 * that wraps each eligible bean with an AOP proxy, delegating to specified interceptors
 * before invoking the bean itself.
 *
 * <p>This class distinguishes between "common" interceptors: shared for all proxies it
 * creates, and "specific" interceptors: unique per bean instance. There need not be any
 * common interceptors. If there are, they are set using the interceptorNames property.
 * As with {@link org.springframework.aop.framework.ProxyFactoryBean}, interceptors names
 * in the current factory are used rather than bean references to allow correct handling
 * of prototype advisors and interceptors: for example, to support stateful mixins.
 * Any advice type is supported for {@link #setInterceptorNames "interceptorNames"} entries.
 *
 * <p>Such auto-proxying is particularly useful if there's a large number of beans that
 * need to be wrapped with similar proxies, i.e. delegating to the same interceptors.
 * Instead of x repetitive proxy definitions for x target beans, you can register
 * one single such post processor with the bean factory to achieve the same effect.
 *
 * <p>Subclasses can apply any strategy to decide if a bean is to be proxied, e.g. by type,
 * by name, by definition details, etc. They can also return additional interceptors that
 * should just be applied to the specific bean instance. A simple concrete implementation is
 * {@link BeanNameAutoProxyCreator}, identifying the beans to be proxied via given names.
 *
 * <p>Any number of {@link TargetSourceCreator} implementations can be used to create
 * a custom target source: for example, to pool prototype objects. Auto-proxying will
 * occur even if there is no advice, as long as a TargetSourceCreator specifies a custom
 * {@link org.springframework.aop.TargetSource}. If there are no TargetSourceCreators set,
 * or if none matches, a {@link org.springframework.aop.target.SingletonTargetSource}
 * will be used by default to wrap the target bean instance.
 *
 * @author Juergen Hoeller
 * @author Rod Johnson
 * @author Rob Harrop
 * @author Sam Brannen
 * @since 13.10.2003
 * @see #setInterceptorNames
 * @see #getAdvicesAndAdvisorsForBean
 * @see BeanNameAutoProxyCreator
 * @see DefaultAdvisorAutoProxyCreator
 */
@SuppressWarnings("serial")
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
		implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {

	/**
	 * Convenience constant for subclasses: Return value for "do not proxy".
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	@Nullable
	protected static final Object[] DO_NOT_PROXY = null;

	/**
	 * Convenience constant for subclasses: Return value for
	 * "proxy without additional interceptors, just the common ones".
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	protected static final Object[] PROXY_WITHOUT_ADDITIONAL_INTERCEPTORS = new Object[0];


	/** Logger available to subclasses. */
	protected final Log logger = LogFactory.getLog(getClass());

	/** Default is global AdvisorAdapterRegistry. */
	private AdvisorAdapterRegistry advisorAdapterRegistry = GlobalAdvisorAdapterRegistry.getInstance();

	/**
	 * Indicates whether the proxy should be frozen. Overridden from super
	 * to prevent the configuration from becoming frozen too early.
	 */
	private boolean freezeProxy = false;

	/** Default is no common interceptors. */
	private String[] interceptorNames = new String[0];

	private boolean applyCommonInterceptorsFirst = true;

	@Nullable
	private TargetSourceCreator[] customTargetSourceCreators;

	@Nullable
	private BeanFactory beanFactory;

	private final Set<String> targetSourcedBeans = Collections.newSetFromMap(new ConcurrentHashMap<>(16));

	private final Map<Object, Object> earlyBeanReferences = new ConcurrentHashMap<>(16);

	private final Map<Object, Class<?>> proxyTypes = new ConcurrentHashMap<>(16);

	private final Map<Object, Boolean> advisedBeans = new ConcurrentHashMap<>(256);


	/**
	 * Set whether the proxy should be frozen, preventing advice
	 * from being added to it once it is created.
	 * <p>Overridden from the superclass to prevent the proxy configuration
	 * from being frozen before the proxy is created.
	 */
	@Override
	public void setFrozen(boolean frozen) {
		this.freezeProxy = frozen;
	}

	@Override
	public boolean isFrozen() {
		return this.freezeProxy;
	}

	/**
	 * Specify the {@link AdvisorAdapterRegistry} to use.
	 * <p>Default is the global {@link AdvisorAdapterRegistry}.
	 * @see org.springframework.aop.framework.adapter.GlobalAdvisorAdapterRegistry
	 */
	public void setAdvisorAdapterRegistry(AdvisorAdapterRegistry advisorAdapterRegistry) {
		this.advisorAdapterRegistry = advisorAdapterRegistry;
	}

	/**
	 * Set custom {@code TargetSourceCreators} to be applied in this order.
	 * If the list is empty, or they all return null, a {@link SingletonTargetSource}
	 * will be created for each bean.
	 * <p>Note that TargetSourceCreators will kick in even for target beans
	 * where no advices or advisors have been found. If a {@code TargetSourceCreator}
	 * returns a {@link TargetSource} for a specific bean, that bean will be proxied
	 * in any case.
	 * <p>{@code TargetSourceCreators} can only be invoked if this post processor is used
	 * in a {@link BeanFactory} and its {@link BeanFactoryAware} callback is triggered.
	 * @param targetSourceCreators the list of {@code TargetSourceCreators}.
	 * Ordering is significant: The {@code TargetSource} returned from the first matching
	 * {@code TargetSourceCreator} (that is, the first that returns non-null) will be used.
	 */
	public void setCustomTargetSourceCreators(TargetSourceCreator... targetSourceCreators) {
		this.customTargetSourceCreators = targetSourceCreators;
	}

	/**
	 * Set the common interceptors. These must be bean names in the current factory.
	 * They can be of any advice or advisor type Spring supports.
	 * <p>If this property isn't set, there will be zero common interceptors.
	 * This is perfectly valid, if "specific" interceptors such as matching
	 * Advisors are all we want.
	 */
	public void setInterceptorNames(String... interceptorNames) {
		this.interceptorNames = interceptorNames;
	}

	/**
	 * Set whether the common interceptors should be applied before bean-specific ones.
	 * Default is "true"; else, bean-specific interceptors will get applied first.
	 */
	public void setApplyCommonInterceptorsFirst(boolean applyCommonInterceptorsFirst) {
		this.applyCommonInterceptorsFirst = applyCommonInterceptorsFirst;
	}

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		this.beanFactory = beanFactory;
	}

	/**
	 * Return the owning {@link BeanFactory}.
	 * May be {@code null}, as this post-processor doesn't need to belong to a bean factory.
	 */
	@Nullable
	protected BeanFactory getBeanFactory() {
		return this.beanFactory;
	}


	@Override
	@Nullable
	public Class<?> predictBeanType(Class<?> beanClass, String beanName) {
		if (this.proxyTypes.isEmpty()) {
			return null;
		}
		Object cacheKey = getCacheKey(beanClass, beanName);
		return this.proxyTypes.get(cacheKey);
	}

	@Override
	public Class<?> determineBeanType(Class<?> beanClass, String beanName) {
		Object cacheKey = getCacheKey(beanClass, beanName);
		Class<?> proxyType = this.proxyTypes.get(cacheKey);
		if (proxyType == null) {
			TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
			if (targetSource != null) {
				if (StringUtils.hasLength(beanName)) {
					this.targetSourcedBeans.add(beanName);
				}
			}
			else {
				targetSource = EmptyTargetSource.forClass(beanClass);
			}
			Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
			if (specificInterceptors != DO_NOT_PROXY) {
				this.advisedBeans.put(cacheKey, Boolean.TRUE);
				proxyType = createProxyClass(beanClass, beanName, specificInterceptors, targetSource);
				this.proxyTypes.put(cacheKey, proxyType);
			}
		}
		return (proxyType != null ? proxyType : beanClass);
	}

	@Override
	@Nullable
	public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName) {
		return null;
	}

	@Override
	public Object getEarlyBeanReference(Object bean, String beanName) {
		Object cacheKey = getCacheKey(bean.getClass(), beanName);
		this.earlyBeanReferences.put(cacheKey, bean);
		return wrapIfNecessary(bean, beanName, cacheKey);
	}

	@Override
	@Nullable
	public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) {
		Object cacheKey = getCacheKey(beanClass, beanName);

		if (!StringUtils.hasLength(beanName) || !this.targetSourcedBeans.contains(beanName)) {
			if (this.advisedBeans.containsKey(cacheKey)) {
				return null;
			}
			if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
				this.advisedBeans.put(cacheKey, Boolean.FALSE);
				return null;
			}
		}

		// Create proxy here if we have a custom TargetSource.
		// Suppresses unnecessary default instantiation of the target bean:
		// The TargetSource will handle target instances in a custom fashion.
		TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
		if (targetSource != null) {
			if (StringUtils.hasLength(beanName)) {
				this.targetSourcedBeans.add(beanName);
			}
			Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
			Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		return null;
	}

	@Override
	public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
		return pvs;  // skip postProcessPropertyValues
	}

	/**
	 * Create a proxy with the configured interceptors if the bean is
	 * identified as one to proxy by the subclass.
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	@Override
	@Nullable
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyBeanReferences.remove(cacheKey) != bean) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}


	/**
	 * Build a cache key for the given bean class and bean name.
	 * <p>Note: As of 4.2.3, this implementation does not return a concatenated
	 * class/name String anymore but rather the most efficient cache key possible:
	 * a plain bean name, prepended with {@link BeanFactory#FACTORY_BEAN_PREFIX}
	 * in case of a {@code FactoryBean}; or if no bean name specified, then the
	 * given bean {@code Class} as-is.
	 * @param beanClass the bean class
	 * @param beanName the bean name
	 * @return the cache key for the given class and name
	 */
	protected Object getCacheKey(Class<?> beanClass, @Nullable String beanName) {
		if (StringUtils.hasLength(beanName)) {
			return (FactoryBean.class.isAssignableFrom(beanClass) ?
					BeanFactory.FACTORY_BEAN_PREFIX + beanName : beanName);
		}
		else {
			return beanClass;
		}
	}

	/**
	 * Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
	 * @param bean the raw bean instance
	 * @param beanName the name of the bean
	 * @param cacheKey the cache key for metadata access
	 * @return a proxy wrapping the bean, or the raw bean instance as-is
	 */
	protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

	/**
	 * Return whether the given bean class represents an infrastructure class
	 * that should never be proxied.
	 * <p>The default implementation considers Advices, Advisors and
	 * AopInfrastructureBeans as infrastructure classes.
	 * @param beanClass the class of the bean
	 * @return whether the bean represents an infrastructure class
	 * @see org.aopalliance.aop.Advice
	 * @see org.springframework.aop.Advisor
	 * @see org.springframework.aop.framework.AopInfrastructureBean
	 * @see #shouldSkip
	 */
	protected boolean isInfrastructureClass(Class<?> beanClass) {
		boolean retVal = Advice.class.isAssignableFrom(beanClass) ||
				Pointcut.class.isAssignableFrom(beanClass) ||
				Advisor.class.isAssignableFrom(beanClass) ||
				AopInfrastructureBean.class.isAssignableFrom(beanClass);
		if (retVal && logger.isTraceEnabled()) {
			logger.trace("Did not attempt to auto-proxy infrastructure class [" + beanClass.getName() + "]");
		}
		return retVal;
	}

	/**
	 * Subclasses should override this method to return {@code true} if the
	 * given bean should not be considered for auto-proxying by this post-processor.
	 * <p>Sometimes we need to be able to avoid this happening, e.g. if it will lead to
	 * a circular reference or if the existing target instance needs to be preserved.
	 * This implementation returns {@code false} unless the bean name indicates an
	 * "original instance" according to {@code AutowireCapableBeanFactory} conventions.
	 * @param beanClass the class of the bean
	 * @param beanName the name of the bean
	 * @return whether to skip the given bean
	 * @see org.springframework.beans.factory.config.AutowireCapableBeanFactory#ORIGINAL_INSTANCE_SUFFIX
	 */
	protected boolean shouldSkip(Class<?> beanClass, String beanName) {
		return AutoProxyUtils.isOriginalInstance(beanName, beanClass);
	}

	/**
	 * Create a target source for bean instances. Uses any TargetSourceCreators if set.
	 * Returns {@code null} if no custom TargetSource should be used.
	 * <p>This implementation uses the "customTargetSourceCreators" property.
	 * Subclasses can override this method to use a different mechanism.
	 * @param beanClass the class of the bean to create a TargetSource for
	 * @param beanName the name of the bean
	 * @return a TargetSource for this bean
	 * @see #setCustomTargetSourceCreators
	 */
	@Nullable
	protected TargetSource getCustomTargetSource(Class<?> beanClass, String beanName) {
		// We can't create fancy target sources for directly registered singletons.
		if (this.customTargetSourceCreators != null &&
				this.beanFactory != null && this.beanFactory.containsBean(beanName)) {
			for (TargetSourceCreator tsc : this.customTargetSourceCreators) {
				TargetSource ts = tsc.getTargetSource(beanClass, beanName);
				if (ts != null) {
					// Found a matching TargetSource.
					if (logger.isTraceEnabled()) {
						logger.trace("TargetSourceCreator [" + tsc +
								"] found custom TargetSource for bean with name '" + beanName + "'");
					}
					return ts;
				}
			}
		}

		// No custom TargetSource found.
		return null;
	}

	/**
	 * Create an AOP proxy for the given bean.
	 * @param beanClass the class of the bean
	 * @param beanName the name of the bean
	 * @param specificInterceptors the set of interceptors that is
	 * specific to this bean (may be empty, but not null)
	 * @param targetSource the TargetSource for the proxy,
	 * already pre-configured to access the bean
	 * @return the AOP proxy for the bean
	 * @see #buildAdvisors
	 */
	protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
			@Nullable Object[] specificInterceptors, TargetSource targetSource) {

		return buildProxy(beanClass, beanName, specificInterceptors, targetSource, false);
	}

	private Class<?> createProxyClass(Class<?> beanClass, @Nullable String beanName,
			@Nullable Object[] specificInterceptors, TargetSource targetSource) {

		return (Class<?>) buildProxy(beanClass, beanName, specificInterceptors, targetSource, true);
	}

	private Object buildProxy(Class<?> beanClass, @Nullable String beanName,
			@Nullable Object[] specificInterceptors, TargetSource targetSource, boolean classOnly) {

		if (this.beanFactory instanceof ConfigurableListableBeanFactory clbf) {
			AutoProxyUtils.exposeTargetClass(clbf, beanName, beanClass);
		}

		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.copyFrom(this);

		if (proxyFactory.isProxyTargetClass()) {
			// Explicit handling of JDK proxy targets and lambdas (for introduction advice scenarios)
			if (Proxy.isProxyClass(beanClass) || ClassUtils.isLambdaClass(beanClass)) {
				// Must allow for introductions; can't just set interfaces to the proxy's interfaces only.
				for (Class<?> ifc : beanClass.getInterfaces()) {
					proxyFactory.addInterface(ifc);
				}
			}
		}
		else {
			// No proxyTargetClass flag enforced, let's apply our default checks...
			if (shouldProxyTargetClass(beanClass, beanName)) {
				proxyFactory.setProxyTargetClass(true);
			}
			else {
				evaluateProxyInterfaces(beanClass, proxyFactory);
			}
		}

		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
		proxyFactory.addAdvisors(advisors);
		proxyFactory.setTargetSource(targetSource);
		customizeProxyFactory(proxyFactory);

		proxyFactory.setFrozen(this.freezeProxy);
		if (advisorsPreFiltered()) {
			proxyFactory.setPreFiltered(true);
		}

		// Use original ClassLoader if bean class not locally loaded in overriding class loader
		ClassLoader classLoader = getProxyClassLoader();
		if (classLoader instanceof SmartClassLoader smartClassLoader && classLoader != beanClass.getClassLoader()) {
			classLoader = smartClassLoader.getOriginalClassLoader();
		}
		return (classOnly ? proxyFactory.getProxyClass(classLoader) : proxyFactory.getProxy(classLoader));
	}

	/**
	 * Determine whether the given bean should be proxied with its target class rather than its interfaces.
	 * <p>Checks the {@link AutoProxyUtils#PRESERVE_TARGET_CLASS_ATTRIBUTE "preserveTargetClass" attribute}
	 * of the corresponding bean definition.
	 * @param beanClass the class of the bean
	 * @param beanName the name of the bean
	 * @return whether the given bean should be proxied with its target class
	 * @see AutoProxyUtils#shouldProxyTargetClass
	 */
	protected boolean shouldProxyTargetClass(Class<?> beanClass, @Nullable String beanName) {
		return (this.beanFactory instanceof ConfigurableListableBeanFactory clbf &&
				AutoProxyUtils.shouldProxyTargetClass(clbf, beanName));
	}

	/**
	 * Return whether the Advisors returned by the subclass are pre-filtered
	 * to match the bean's target class already, allowing the ClassFilter check
	 * to be skipped when building advisors chains for AOP invocations.
	 * <p>Default is {@code false}. Subclasses may override this if they
	 * will always return pre-filtered Advisors.
	 * @return whether the Advisors are pre-filtered
	 * @see #getAdvicesAndAdvisorsForBean
	 * @see org.springframework.aop.framework.Advised#setPreFiltered
	 */
	protected boolean advisorsPreFiltered() {
		return false;
	}

	/**
	 * Determine the advisors for the given bean, including the specific interceptors
	 * as well as the common interceptor, all adapted to the Advisor interface.
	 * @param beanName the name of the bean
	 * @param specificInterceptors the set of interceptors that is
	 * specific to this bean (may be empty, but not null)
	 * @return the list of Advisors for the given bean
	 */
	protected Advisor[] buildAdvisors(@Nullable String beanName, @Nullable Object[] specificInterceptors) {
		// Handle prototypes correctly...
		Advisor[] commonInterceptors = resolveInterceptorNames();

		List<Object> allInterceptors = new ArrayList<>();
		if (specificInterceptors != null) {
			if (specificInterceptors.length > 0) {
				// specificInterceptors may equal PROXY_WITHOUT_ADDITIONAL_INTERCEPTORS
				allInterceptors.addAll(Arrays.asList(specificInterceptors));
			}
			if (commonInterceptors.length > 0) {
				if (this.applyCommonInterceptorsFirst) {
					allInterceptors.addAll(0, Arrays.asList(commonInterceptors));
				}
				else {
					allInterceptors.addAll(Arrays.asList(commonInterceptors));
				}
			}
		}
		if (logger.isTraceEnabled()) {
			int nrOfCommonInterceptors = commonInterceptors.length;
			int nrOfSpecificInterceptors = (specificInterceptors != null ? specificInterceptors.length : 0);
			logger.trace("Creating implicit proxy for bean '" + beanName + "' with " + nrOfCommonInterceptors +
					" common interceptors and " + nrOfSpecificInterceptors + " specific interceptors");
		}

		Advisor[] advisors = new Advisor[allInterceptors.size()];
		for (int i = 0; i < allInterceptors.size(); i++) {
			advisors[i] = this.advisorAdapterRegistry.wrap(allInterceptors.get(i));
		}
		return advisors;
	}

	/**
	 * Resolves the specified interceptor names to Advisor objects.
	 * @see #setInterceptorNames
	 */
	private Advisor[] resolveInterceptorNames() {
		BeanFactory bf = this.beanFactory;
		ConfigurableBeanFactory cbf = (bf instanceof ConfigurableBeanFactory _cbf ? _cbf : null);
		List<Advisor> advisors = new ArrayList<>();
		for (String beanName : this.interceptorNames) {
			if (cbf == null || !cbf.isCurrentlyInCreation(beanName)) {
				Assert.state(bf != null, "BeanFactory required for resolving interceptor names");
				Object next = bf.getBean(beanName);
				advisors.add(this.advisorAdapterRegistry.wrap(next));
			}
		}
		return advisors.toArray(new Advisor[0]);
	}

	/**
	 * Subclasses may choose to implement this: for example,
	 * to change the interfaces exposed.
	 * <p>The default implementation is empty.
	 * @param proxyFactory a ProxyFactory that is already configured with
	 * TargetSource and interfaces and will be used to create the proxy
	 * immediately after this method returns
	 */
	protected void customizeProxyFactory(ProxyFactory proxyFactory) {
	}


	/**
	 * Return whether the given bean is to be proxied, what additional
	 * advices (e.g. AOP Alliance interceptors) and advisors to apply.
	 * @param beanClass the class of the bean to advise
	 * @param beanName the name of the bean
	 * @param customTargetSource the TargetSource returned by the
	 * {@link #getCustomTargetSource} method: may be ignored.
	 * Will be {@code null} if no custom target source is in use.
	 * @return an array of additional interceptors for the particular bean;
	 * or an empty array if no additional interceptors but just the common ones;
	 * or {@code null} if no proxy at all, not even with the common interceptors.
	 * See constants DO_NOT_PROXY and PROXY_WITHOUT_ADDITIONAL_INTERCEPTORS.
	 * @throws BeansException in case of errors
	 * @see #DO_NOT_PROXY
	 * @see #PROXY_WITHOUT_ADDITIONAL_INTERCEPTORS
	 */
	@Nullable
	protected abstract Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName,
			@Nullable TargetSource customTargetSource) throws BeansException;

}

代理工厂有一个重要的属性: proxyTargetClass,默认值为false.也可以通过程序设置

Spring Boot 2.X开始,默认使用CGLIB代理

可以通过配置项 spring.aop.proxy-target-class=false 来进行修改, 设置默认为jdk代理

SpringBoot设置 @EnableAspectJAutoProxy 无效, 因为Spring Boot 默认使用

AopAutoConfiguration 进行装配

我看点进去看代理⼯⼚的代码

/**
 * Factory for AOP proxies for programmatic use, rather than via declarative
 * setup in a bean factory. This class provides a simple way of obtaining
 * and configuring AOP proxy instances in custom user code.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 14.03.2003
 */
@SuppressWarnings("serial")
public class ProxyFactory extends ProxyCreatorSupport {

	/**
	 * Create a new ProxyFactory.
	 */
	public ProxyFactory() {
	}

	/**
	 * Create a new ProxyFactory.
	 * <p>Will proxy all interfaces that the given target implements.
	 * @param target the target object to be proxied
	 */
	public ProxyFactory(Object target) {
		setTarget(target);
		setInterfaces(ClassUtils.getAllInterfaces(target));
	}

	/**
	 * Create a new ProxyFactory.
	 * <p>No target, only interfaces. Must add interceptors.
	 * @param proxyInterfaces the interfaces that the proxy should implement
	 */
	public ProxyFactory(Class<?>... proxyInterfaces) {
		setInterfaces(proxyInterfaces);
	}

	/**
	 * Create a new ProxyFactory for the given interface and interceptor.
	 * <p>Convenience method for creating a proxy for a single interceptor,
	 * assuming that the interceptor handles all calls itself rather than
	 * delegating to a target, like in the case of remoting proxies.
	 * @param proxyInterface the interface that the proxy should implement
	 * @param interceptor the interceptor that the proxy should invoke
	 */
	public ProxyFactory(Class<?> proxyInterface, Interceptor interceptor) {
		addInterface(proxyInterface);
		addAdvice(interceptor);
	}

	/**
	 * Create a ProxyFactory for the specified {@code TargetSource},
	 * making the proxy implement the specified interface.
	 * @param proxyInterface the interface that the proxy should implement
	 * @param targetSource the TargetSource that the proxy should invoke
	 */
	public ProxyFactory(Class<?> proxyInterface, TargetSource targetSource) {
		addInterface(proxyInterface);
		setTargetSource(targetSource);
	}


	/**
	 * Create a new proxy according to the settings in this factory.
	 * <p>Can be called repeatedly. Effect will vary if we've added
	 * or removed interfaces. Can add and remove interceptors.
	 * <p>Uses a default class loader: Usually, the thread context class loader
	 * (if necessary for proxy creation).
	 * @return the proxy object
	 */
	public Object getProxy() {
		return createAopProxy().getProxy();
	}

	/**
	 * Create a new proxy according to the settings in this factory.
	 * <p>Can be called repeatedly. Effect will vary if we've added
	 * or removed interfaces. Can add and remove interceptors.
	 * <p>Uses the given class loader (if necessary for proxy creation).
	 * @param classLoader the class loader to create the proxy with
	 * (or {@code null} for the low-level proxy facility's default)
	 * @return the proxy object
	 */
	public Object getProxy(@Nullable ClassLoader classLoader) {
		return createAopProxy().getProxy(classLoader);
	}

	/**
	 * Determine the proxy class according to the settings in this factory.
	 * @param classLoader the class loader to create the proxy class with
	 * (or {@code null} for the low-level proxy facility's default)
	 * @return the proxy class
	 * @since 6.0
	 */
	public Class<?> getProxyClass(@Nullable ClassLoader classLoader) {
		return createAopProxy().getProxyClass(classLoader);
	}


	/**
	 * Create a new proxy for the given interface and interceptor.
	 * <p>Convenience method for creating a proxy for a single interceptor,
	 * assuming that the interceptor handles all calls itself rather than
	 * delegating to a target, like in the case of remoting proxies.
	 * @param proxyInterface the interface that the proxy should implement
	 * @param interceptor the interceptor that the proxy should invoke
	 * @return the proxy object
	 * @see #ProxyFactory(Class, org.aopalliance.intercept.Interceptor)
	 */
	@SuppressWarnings("unchecked")
	public static <T> T getProxy(Class<T> proxyInterface, Interceptor interceptor) {
		return (T) new ProxyFactory(proxyInterface, interceptor).getProxy();
	}

	/**
	 * Create a proxy for the specified {@code TargetSource},
	 * implementing the specified interface.
	 * @param proxyInterface the interface that the proxy should implement
	 * @param targetSource the TargetSource that the proxy should invoke
	 * @return the proxy object
	 * @see #ProxyFactory(Class, org.springframework.aop.TargetSource)
	 */
	@SuppressWarnings("unchecked")
	public static <T> T getProxy(Class<T> proxyInterface, TargetSource targetSource) {
		return (T) new ProxyFactory(proxyInterface, targetSource).getProxy();
	}

	/**
	 * Create a proxy for the specified {@code TargetSource} that extends
	 * the target class of the {@code TargetSource}.
	 * @param targetSource the TargetSource that the proxy should invoke
	 * @return the proxy object
	 */
	public static Object getProxy(TargetSource targetSource) {
		if (targetSource.getTargetClass() == null) {
			throw new IllegalArgumentException("Cannot create class proxy for TargetSource with null target class");
		}
		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.setTargetSource(targetSource);
		proxyFactory.setProxyTargetClass(true);
		return proxyFactory.getProxy();
	}

}

createAopProxy的实现在 DefaultAopProxyFactory中

/**
 * Default {@link AopProxyFactory} implementation, creating either a CGLIB proxy
 * or a JDK dynamic proxy.
 *
 * <p>Creates a CGLIB proxy if one the following is true for a given
 * {@link AdvisedSupport} instance:
 * <ul>
 * <li>the {@code optimize} flag is set
 * <li>the {@code proxyTargetClass} flag is set
 * <li>no proxy interfaces have been specified
 * </ul>
 *
 * <p>In general, specify {@code proxyTargetClass} to enforce a CGLIB proxy,
 * or specify one or more interfaces to use a JDK dynamic proxy.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @author Sam Brannen
 * @since 12.03.2004
 * @see AdvisedSupport#setOptimize
 * @see AdvisedSupport#setProxyTargetClass
 * @see AdvisedSupport#setInterfaces
 */
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {

	/**
	 * Singleton instance of this class.
	 * @since 6.0.10
	 */
	public static final DefaultAopProxyFactory INSTANCE = new DefaultAopProxyFactory();

	private static final long serialVersionUID = 7930414337282325166L;


	@Override
	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
		if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
			Class<?> targetClass = config.getTargetClass();
			if (targetClass == null) {
				throw new AopConfigException("TargetSource cannot determine target class: " +
						"Either an interface or a target is required for proxy creation.");
			}
			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass) || ClassUtils.isLambdaClass(targetClass)) {
				return new JdkDynamicAopProxy(config);
			}
			return new ObjenesisCglibAopProxy(config);
		}
		else {
			return new JdkDynamicAopProxy(config);
		}
	}

	/**
	 * Determine whether the supplied {@link AdvisedSupport} has only the
	 * {@link org.springframework.aop.SpringProxy} interface specified
	 * (or no proxy interfaces specified at all).
	 */
	private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
		Class<?>[] ifcs = config.getProxiedInterfaces();
		return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
	}

}

接下来就是创建代理了

JDK动态代理

CGLIB动态代理

CglibAopProxy类中:

@Override
	public Object getProxy(@Nullable ClassLoader classLoader) {
		return buildProxy(classLoader, false);
	}

	@Override
	public Class<?> getProxyClass(@Nullable ClassLoader classLoader) {
		return (Class<?>) buildProxy(classLoader, true);
	}

	private Object buildProxy(@Nullable ClassLoader classLoader, boolean classOnly) {
		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 &&
						smartClassLoader.isClassReloadable(proxySuperClass)) {
					enhancer.setUseCache(false);
				}
			}
			enhancer.setSuperclass(proxySuperClass);
			enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
			enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
			enhancer.setAttemptLoad(true);
			enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));

			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
			ProxyCallbackFilter filter = new ProxyCallbackFilter(
					this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset);
			enhancer.setCallbackFilter(filter);
			enhancer.setCallbackTypes(types);

			// Generate the proxy class and create a proxy instance.
			// ProxyCallbackFilter has method introspection capability with Advisor access.
			try {
				return (classOnly ? createProxyClass(enhancer) : createProxyClassAndInstance(enhancer, callbacks));
			}
			finally {
				// Reduce ProxyCallbackFilter to key-only state for its class cache role
				// in the CGLIB$CALLBACK_FILTER field, not leaking any Advisor state...
				filter.advised.reduceToAdvisorKey();
			}
		}
		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);
		}
	}

回顾:

1.什么是AOP

2.SpringAOP 的实现方式有哪些?

3.SpringAOP 的实现原理 (基于动态代理 1.JDK 2.CGLib)

4. Spring 使用的是那种代理方式?

Spring 默认 proxyTargetClass 值为false, 如果实现了接口, 使用JDK代理, 如果是普通类则使用CGLib代理

SpringBoot从2.x之后, proxyTargetClass值为true, 默认是使用CGLib代理

5. JDK动态代理和CGLib动态代理的区别?

总结