定义和类型
使用场景
优点
缺点
扩展
Spring 代理
代理速度对比
相关设计模式
2 实战
2.1 静态代理
看 UML 图
展开包节点
image.png
动态代理
源码分析
/**
* Returns an instance of a proxy class for the specified interfaces
* that dispatches method invocations to the specified invocation
* handler.
*
* <p>{@code Proxy.newProxyInstance} throws
* {@code IllegalArgumentException} for the same reasons that
* {@code Proxy.getProxyClass} does.
*
* @param loader the class loader to define the proxy class
* @param interfaces the list of interfaces for the proxy class
* to implement
* @param h the invocation handler to dispatch method invocations to
* @return a proxy instance with the specified invocation handler of a
* proxy class that is defined by the specified class loader
* and that implements the specified interfaces
* @throws IllegalArgumentException if any of the restrictions on the
* parameters that may be passed to {@code getProxyClass}
* are violated
* @throws SecurityException if a security manager, <em>s</em>, is present
* and any of the following conditions is met:
* <ul>
* <li> the given {@code loader} is {@code null} and
* the caller's class loader is not {@code null} and the
* invocation of {@link SecurityManager#checkPermission
* s.checkPermission} with
* {@code RuntimePermission("getClassLoader")} permission
* denies access;</li>
* <li> for each proxy interface, {@code intf},
* the caller's class loader is not the same as or an
* ancestor of the class loader for {@code intf} and
* invocation of {@link SecurityManager#checkPackageAccess
* s.checkPackageAccess()} denies access to {@code intf};</li>
* <li> any of the given proxy interfaces is non-public and the
* caller class is not in the same {@linkplain Package runtime package}
* as the non-public interface and the invocation of
* {@link SecurityManager#checkPermission s.checkPermission} with
* {@code ReflectPermission("newProxyInPackage.{package name}")}
* permission denies access.</li>
* </ul>
* @throws NullPointerException if the {@code interfaces} array
* argument or any of its elements are {@code null}, or
* if the invocation handler, {@code h}, is
* {@code null}
*/
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces,InvocationHandler h) throws IllegalArgumentException { // 检查代理对象非空
Objects.requireNonNull(h);
// 安全检查
final Class<?>[] intfs = interfaces.clone(); final SecurityManager sm = System.getSecurityManager(); if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
} /*
* Look up or generate the designated proxy class.
*/
Class<?> cl = getProxyClass0(loader, intfs);
生成代理类实现方法
检查接口数量
代理缓存
/**
* Look-up the value through the cache. This always evaluates the
* {@code subKeyFactory} function and optionally evaluates
* {@code valueFactory} function if there is no entry in the cache for given
* pair of (key, subKey) or the entry has already been cleared.
*
* @param key possibly null key
* @param parameter parameter used together with key to create sub-key and
* value (should not be null)
* @return the cached value (never null)
* @throws NullPointerException if {@code parameter} passed in or
* {@code sub-key} calculated by
* {@code subKeyFactory} or {@code value}
* calculated by {@code valueFactory} is null.
*/
public V get(K key, P parameter) {
Objects.requireNonNull(parameter);
expungeStaleEntries();
Object cacheKey = CacheKey.valueOf(key, refQueue); // lazily install the 2nd level valuesMap for the particular cacheKey
ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey); if (valuesMap == null) {
ConcurrentMap<Object, Supplier<V>> oldValuesMap
= map.putIfAbsent(cacheKey,
valuesMap = new ConcurrentHashMap<>()); if (oldValuesMap != null) {
valuesMap = oldValuesMap;
}
} // create subKey and retrieve the possible Supplier<V> stored by that
// subKey from valuesMap
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
Supplier<V> supplier = valuesMap.get(subKey);
Factory factory = null; while (true) { if (supplier != null) { // supplier might be a Factory or a CacheValue<V> instance
V value = supplier.get(); if (value != null) { return value;
}
} // else no supplier in cache
// or a supplier that returned null (could be a cleared CacheValue
// or a Factory that wasn't successful in installing the CacheValue)
// lazily construct a Factory
if (factory == null) {
factory = new Factory(key, parameter, subKey, valuesMap);
} if (supplier == null) {
supplier = valuesMap.putIfAbsent(subKey, factory); if (supplier == null) { // successfully installed Factory
supplier = factory;
} // else retry with winning supplier
} else { if (valuesMap.replace(subKey, supplier, factory)) { // successfully replaced
// cleared CacheEntry / unsuccessful Factory
// with our Factory
supplier = factory;
} else { // retry with current supplier
supplier = valuesMap.get(subKey);
}
}
}
} /*
* Invoke its constructor with the designated invocation handler.
*/
try { if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
} final Constructor<?> cons = cl.getConstructor(constructorParams); final InvocationHandler ih = h; if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() { public Void run() {
cons.setAccessible(true); return null;
}
});
} return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) { throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause(); if (t instanceof RuntimeException) { throw (RuntimeException) t;
} else { throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) { throw new InternalError(e.toString(), e);
}
}Spring 使用示例
Spring自己的AOP，搞清楚哪种方式是Spring自己实现的AOP，哪种方式是Spring引入aspectj的AOP。
Spring自己的AOP实现在于ProxyFactoryBean。先看下使用案例
接口MyService
实现类MyServiceImpl
通知MyBeforeAdvice
然后就是xml的配置：
<bean id="aServiceImpl" class="com.lg.aop.service.impl.AServiceImpl"/> <bean id="myBeforAdvice" class="com.lg.aop.MyBeforeAdvice"/> <bean class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="interfaces" value="com.lg.aop.service.AService"/> <property name="target"> <ref bean="aServiceImpl"/> </property> <property name="interceptorNames"> <list> <value>myBeforAdvice</value> </list> </property> </bean>
然后就可以使用了：
@Autowired
private AService aService; @Test
public void testAOP(){
aService.barA();
}运行这个单元测试，然后你就会看到报如下错误：
No qualifying bean of type [com.lg.aop.service.AService] is defined: expected single matching bean but found 2: aServiceImpl,org.springframework.aop.framework.ProxyFactoryBean#0
对于接口MyService，有两个实现类MyServiceImpl和ProxyFactoryBean所生产的代理类
所以我们不能使用@Autowired（它是按类型注入），要使用按名称注入，我们怎么获取ProxyFactoryBean所产生的代理类的名称呢？
其实就是ProxyFactoryBean配置的名称。因为ProxyFactoryBean实现了FactoryBean接口
对于这种接口从容器中获取该bean，不是获取的本身而是获取其getObject方法所返回的值，看FactoryBean的文档：
/**
* Interface to be implemented by objects used within a {@link BeanFactory}
* which are themselves factories. If a bean implements this interface,
* it is used as a factory for an object to expose, not directly as a bean
* instance that will be exposed itself.
*
* <p><b>NB: A bean that implements this interface cannot be used as a
* normal bean.</b> A FactoryBean is defined in a bean style, but the
* object exposed for bean references ({@link #getObject()} is always
* the object that it creates.所以通过beanName找到了ProxyFactoryBean，然而不是返回该对象，而是返回他的getObject方法的返回值，所以我们通过ProxyFactoryBean的id就可以获取到它所产生的代理对象，所以更改如下：
<bean id="MyServiceImplProxy" class="org.springframework.aop.framework.ProxyFactoryBean"> ...
在使用注入的时候按名称注入
@Resource(name="MyServiceImplProxy") private AService aService;
然后就可以正常运行了如下：
Run my before adviceMyServiceImpl.barA()
然后我们就要源码分析下这一过程，先看下是如何产生代理对象的，在ProxyFactoryBean的getObject方法中：
重点1：就是根据我们配置的interceptorNames来获取对应的bean，并转化成Advisor
private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException { if (this.advisorChainInitialized) { return;
} if (!ObjectUtils.isEmpty(this.interceptorNames)) { if (this.beanFactory == null) { throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " + "- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames));
} // Globals can't be last unless we specified a targetSource using the property...
if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) && this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) { throw new AopConfigException("Target required after globals");
} // Materialize interceptor chain from bean names.
for (String name : this.interceptorNames) { if (logger.isTraceEnabled()) {
logger.trace("Configuring advisor or advice '" + name + "'");
} if (name.endsWith(GLOBAL_SUFFIX)) { if (!(this.beanFactory instanceof ListableBeanFactory)) { throw new AopConfigException( "Can only use global advisors or interceptors with a ListableBeanFactory");
}
addGlobalAdvisor((ListableBeanFactory) this.beanFactory,
name.substring(0, name.length() - GLOBAL_SUFFIX.length()));
} else { // If we get here, we need to add a named interceptor.
// We must check if it's a singleton or prototype.
Object advice; if (this.singleton || this.beanFactory.isSingleton(name)) { // Add the real Advisor/Advice to the chain.
advice = this.beanFactory.getBean(name);
} else { // It's a prototype Advice or Advisor: replace with a prototype.
// Avoid unnecessary creation of prototype bean just for advisor chain initialization.
advice = new PrototypePlaceholderAdvisor(name);
}
addAdvisorOnChainCreation(advice, name);
}
}
} this.advisorChainInitialized = true;
}advisorChainInitialized：标示是否已初始化，若已初始化则不再进行初始化
然后就是将interceptorNames转化成Advisor
根据interceptorNames所包含的字符串到容器中进行查找，如果含有*则表示进行一定的匹配，符合的都会纳入
<bean id="proxy" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="service"/> <property name="interceptorNames"> <list> <value>global*</value> </list> </property></bean><bean id="global_debug" class="org.springframework.aop.interceptor.DebugInterceptor"/><bean id="global_performance" class="org.springframework.aop.interceptor.PerformanceMonitorInterceptor"/>
这中间也经过了Advice到Advisor的转换
/**
* Invoked when advice chain is created.
* <p>Add the given advice, advisor or object to the interceptor list.
* Because of these three possibilities, we can't type the signature
* more strongly.
* @param next advice, advisor or target object
* @param name bean name from which we obtained this object in our owning
* bean factory
*/
private void addAdvisorOnChainCreation(Object next, String name) { // We need to convert to an Advisor if necessary so that our source reference
// matches what we find from superclass interceptors.
Advisor advisor = namedBeanToAdvisor(next); if (logger.isTraceEnabled()) {
logger.trace("Adding advisor with name '" + name + "'");
}
addAdvisor(advisor);
}private Advisor namedBeanToAdvisor(Object next) { try { return this.advisorAdapterRegistry.wrap(next);
}
}
}public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException { if (adviceObject instanceof Advisor) { return (Advisor) adviceObject;
} if (!(adviceObject instanceof Advice)) { throw new UnknownAdviceTypeException(adviceObject);
}
Advice advice = (Advice) adviceObject; if (advice instanceof MethodInterceptor) { // So well-known it doesn't even need an adapter.
return new DefaultPointcutAdvisor(advice);
} for (AdvisorAdapter adapter : this.adapters) { // Check that it is supported.
if (adapter.supportsAdvice(advice)) { return new DefaultPointcutAdvisor(advice);
}
} throw new UnknownAdviceTypeException(advice);
}这个包裹过程，采用了适配器模式
之后又是和其他的AOP方式接轨了，设置一些列要实现的接口和参数，使用DefaultAopProxyFactory先创建出AopProxy，然后就可以调用AopProxy的getProxy方法来获取代理对象了
这种方式实现的AOP还是比较麻烦的，同时配置一个ProxyFactoryBean仅能实现对一个目标对象的拦截，要想拦截多个目标对象，需要配置多个ProxyFactoryBean
所以大部分还是使用Spring引进的aspectj的AOP方式来进行AOP编程
JdkDynamicAopProxy使用实例
代理类是由默认AOP代理工厂DefaultAopProxyFactory中createAopProxy方法产生的
如果代理对象是接口类型，则生成JdkDynamicAopProxy代理
否则生成ObjenesisCglibAopProxy代理，ObjenesisCglibAopProxy代理是继承于CglibAopProxy
从熟悉的入手，选择JdkDynamicAopProxy分析
构造器
一个final类，不能被继承和实现
JdkDynamicAopProxy依赖于AdvisedSupport，根据config配置信息创建动态代理对象
getProxy
实现AopProxy接口,在创建代理时，既可以采用默认的类加载器，也可以指定特定的类加载器
JDK动态代理的代理对象是接口类型，先获取被代理对象的完整接口、根据指定的类加载器以及实现的调用处理器应用静态方法Proxy.newProxyInstance创建代理对象
@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());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces); return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
} /**
* 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;
}
}
}
}invoke
该类实现了InvocationHandler 接口，必然实现invoke方法
/**
* Implementation of {@code InvocationHandler.invoke}.
* <p>Callers will see exactly the exception thrown by the target,
* unless a hook method throws an exception.
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation; Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Class<?> targetClass = null; Object target = null; try { if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) { // The target does not implement the equals(Object) method itself.
return equals(args[0]);
} if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) { // The target does not implement the hashCode() method itself.
return hashCode();
} 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.
// 得到被代理对象的类名
target = targetSource.getTarget(); if (target != null) {
targetClass = target.getClass();
} // Get the interception chain for this method
// 根据被代理类名和方法名得到通知链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass); // 如果通知链为空，则直接反射调用被代理方法，
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.
// 反射执行被代理方法
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
} else { // 否则创建代理方法
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); // Proceed to the joinpoint through the interceptor chain.
// 执行代理方法
retVal = invocation.proceed();
} // Massage return value if necessary.
Class<?> returnType = method.getReturnType(); if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) { // Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
} else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) { throw new AopInvocationException("Null return value from advice does not match primitive return type for: " + method);
} return retVal;
} finally { if (target != null && !targetSource.isStatic()) { // Must have come from TargetSource.
targetSource.releaseTarget(target);
} if (setProxyContext) { // Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}反射执行被代理方法是调用工具类AopUtils中方法invokeJoinpointUsingReflection实现的，具体如下：
/**
* Invoke the given target via reflection, as part of an AOP method invocation.
* @param target the target object
* @param method the method to invoke
* @param args the arguments for the method
* @return the invocation result, if any
* @throws Throwable if thrown by the target method
* @throws org.springframework.aop.AopInvocationException in case of a reflection error
*/
public static Object invokeJoinpointUsingReflection(Object target, Method method, Object[] args)
throws Throwable { // Use reflection to invoke the method.
try {
ReflectionUtils.makeAccessible(method); return method.invoke(target, args);
} catch (InvocationTargetException ex) { // Invoked method threw a checked exception.
// We must rethrow it. The client won't see the interceptor.
throw ex.getTargetException();
} catch (IllegalArgumentException ex) { throw new AopInvocationException("AOP configuration seems to be invalid: tried calling method [" +
method + "] on target [" + target + "]", ex);
} catch (IllegalAccessException ex) { throw new AopInvocationException("Could not access method [" + method + "]", ex);
}
}创建代理方法是通过ReflectiveMethodInvocation实现的，然后调用proceed()方法执行拦截链和被代理方法。ReflectiveMethodInvocation实现了Joinpoint接口，其构造器如下：
/**
* Construct a new ReflectiveMethodInvocation with the given arguments.
* @param proxy the proxy object that the invocation was made on
* @param target the target object to invoke
* @param method the method to invoke
* @param arguments the arguments to invoke the method with
* @param targetClass the target class, for MethodMatcher invocations
* @param interceptorsAndDynamicMethodMatchers interceptors that should be applied,
* along with any InterceptorAndDynamicMethodMatchers that need evaluation at runtime.
* MethodMatchers included in this struct must already have been found to have matched
* as far as was possibly statically. Passing an array might be about 10% faster,
* but would complicate the code. And it would work only for static pointcuts.
*/
protected ReflectiveMethodInvocation(
Object proxy, Object target, Method method, Object[] arguments,
Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers) { this.proxy = proxy; this.target = target; this.targetClass = targetClass; this.method = BridgeMethodResolver.findBridgedMethod(method); this.arguments = arguments; this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;
}ReflectiveMethodInvocation调用proceed方法执行代理，proceed方法是在Joinpoint接口中定义的，ReflectiveMethodInvocation中进行了实现。具体实现如下：
@Override
public Object proceed() throws Throwable { // We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) { return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex); if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) { // Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice; if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) { return dm.interceptor.invoke(this);
} else { // Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
} else { // It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}从上面分析源码大致可以了解Spring AOP 动态代理的设计思想，采用类加载器根据接口产生代理方法，代理方法是在原方法的基础上加上通知链，以实现AOP功能。当执行方法时，判断该方法通知链是否为空，若为空，则通过反射直接调用原方法；若不为空，则产生代理方法，执行代理方法
MapperProxyFactory
在MyBatis中Mapper文件中的方法和xml配置文件中的SQL映射最重要的3个类就是MapperProxyFactoryMapperProxyMapperMethod
弄懂这3个类你就理解Mapper接口与SQL的映射，为什么是接口，没有实例类也可以完成注入或者调用。
在调用MyBatis的addMapper的时候如果你跟踪源码就会最终跟到MapperRegistry的addMapper中有如下的语句：
type就是Mapper接口
MapperProxyFactory
一看名字我们就知道肯定是一个工厂类，就是为了生成MapperProxy
其实MapperProxyFactory也非常简单
2个成员
就是Mapper接口
对Mapper接口中的方法和方法的封装类（MapperMethod）的映射
MapperMethod主要：处理Mapper接口中方法的注解，参数，和返回值
2个newInstance方法
工厂方法
public方法
参数SqlSession:处理执行一次SQL的过程
public的newInstance就是new了一个MapperProxy,然后调用了protected的newInstance
protected的newInstance
protected简单明了，就是使用Java Proxy的工厂方法生成一个了Mapper接口的代理类
在MapperRegistry中调用了该方法
MapperProxy
MapperProxy实现了InvocationHandlerMapperProxy#invoke则把Method包装成了MapperMethod
MapperMethod处理Mapper接口方法与xml映射的关系,处理方法的注解，参数，返回值，参数与SQL语句中的参数的对应关系
MapperProxy实现了InvocationHandler接口，基于Java动态代理
首先检查如果是Object类中方法就直接调用
如果不是就把方法包装成MapperMethod
因为把Method处理为MapperMethod还是一个比较重的操作，所以这里做了缓存处理
享元模式实例
作者：芥末无疆sss
链接：https://www.jianshu.com/p/7596ae4398db
随时随地看视频
