一、JDK动态代理和CGLIB代理方式:
1、如果目标对象实现了接口,默认会采用JDK代理实现AOP,也可以通过配置强制使用CGLIB实现
2、如果目标对象没有实现接口，必须采用CGLIB库，Spring会自动在JDK方式和CGLIB方式之前转换。
强制使用CGLIB实现：
1.添加CGLIB库,home目录下/cglib/*.jar
2.在spring applicationContext.xml 配置文件中添加<aop:aspectj-autoproxy proxy-target-class="true"/>
JDK动态代理和CGLIB字节码生成的区别:
jdk方式只能针对实现了接口的类，而不能针对类
cglib方式是针对类实现代理，主要是对指定的类生成一个子类，覆盖其中的方法,因为会用到继承，所有目标类和方法不要声明为final
CGLIB包底层通过使用一个小而快的字节码处理框架ASM,来转换字节码并生成新的类,如Groovy和BeanShell,都是使用ASM来生成字节码的。
接着上一节的 spring aop
ProxyFactory类
/**
* 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();
}
JdkDynamicAopProxy类
JdkDynamicAopProxy 类getProxy 追溯到在父类AbstractAutoProxyCreator的postProcessAfterInitialization方法
然后追溯 到refresh方法的doCreate方法 然后再到getBean()方法，也就是BeanFactory接口获取bean的时候就会先查找这个bean里面的所有增强advice,并创建好aop代理Proxy，然后调用的时候就可以调用invoke方法。
@Override
public Object getProxy() {
return getProxy(ClassUtils.getDefaultClassLoader());
}
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this); }
/**
* Implementation of {@code InvocationHandler.invoke}.
* <p>Callers will see exactly the exception thrown by the target,
* unless a hook method throws an exception.
*/
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
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.
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;
}
// 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);
// Get the interception chain for this method. //获取拦截器链
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()) { //如果没有拦截器直接调用切点方法
// 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 { //ReflectiveMethodInvocation把拦截器链chain传给了interceptorsAndDynamicMethodMatchers
// We need to create a method invocation... 将拦截器封装到ReflectiveMethodInvocation类
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed(); //执行拦截器链
}
// 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);
}
}
}
isAssignableFrom：
class1.isAssignableFrom(class2) 判定此 Class 对象所表示的类或接口与指定的 Class 参数所表示的类或接口是否相同，或是否是其超类或超接口。如果是则返回 true；否则返回 false
JDK动态代理的关键是创建InvocationHandler,
主要是 构造函数,invoke方法,getProxy方法
例子:
public class Tests {
public interface AService{
void test();
}
public class AServiceImpl implements AService{
public void test(){
System.out.println("---test---");
}
}
public class MyInvocationHandler implements InvocationHandler{
private Object target;//目标对象
public MyInvocationHandler(Object target) {
super();
this.target = target;
}
@Override //执行目标对象的方法
public Object invoke(Object proxy, Method method, Object[] arg2) throws Throwable {
Object result = method.invoke(target, arg2);
return result;
}
public Object getProxy(){ //获取目标对象的代理对象 classLoader指定一个类加载器来加载所生成的代理类的字节码
ClassLoader classLoader = target.getClass().getClassLoader(); //用这个classLoader和Thread.currentThread().getContextClassLoader()的classLoader都能正确代理
//return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), target.getClass().getInterfaces(), this);
return Proxy.newProxyInstance(classLoader, target.getClass().getInterfaces(), this);
}
}
@Test
public void testProxy(){
AService a = new AServiceImpl();
MyInvocationHandler in = new MyInvocationHandler(a);
AService proxy = (AService)in.getProxy();
proxy.test();
}
}
输出：---test---；
ReflectiveMethodInvocation类
@Override
@Nullable
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
//获取下一个要执行的拦截器
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.//普通拦截器，直接调用
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
二、拦截器
@FunctionalInterface
public interface MethodInterceptor extends Interceptor {
/**
* Implement this method to perform extra treatments before and
* after the invocation. Polite implementations would certainly
* like to invoke {@link Joinpoint#proceed()}.
* @param invocation the method invocation joinpoint
* @return the result of the call to {@link Joinpoint#proceed()};
* might be intercepted by the interceptor
* @throws Throwable if the interceptors or the target object
* throws an exception
*/
Object invoke(MethodInvocation invocation) throws Throwable;
}
1、MethodBeforeAdviceInterceptor
/**
* Interceptor to wrap am {@link org.springframework.aop.MethodBeforeAdvice}.
* Used internally by the AOP framework; application developers should not need
* to use this class directly.
*
* @author Rod Johnson
*/
@SuppressWarnings("serial")
public class MethodBeforeAdviceInterceptor implements MethodInterceptor, Serializable {
private MethodBeforeAdvice advice; //代表了前置增强AspectMethodBeforeAdvice
/**
* Create a new MethodBeforeAdviceInterceptor for the given advice.
* @param advice the MethodBeforeAdvice to wrap
*/
public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
Assert.notNull(advice, "Advice must not be null");
this.advice = advice;
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
return mi.proceed();
}
}
@SuppressWarnings("serial")
public class AspectJMethodBeforeAdvice extends AbstractAspectJAdvice implements MethodBeforeAdvice, Serializable {
public AspectJMethodBeforeAdvice(
Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {
super(aspectJBeforeAdviceMethod, pointcut, aif);
}
@Override
public void before(Method method, Object[] args, @Nullable Object target) throws Throwable {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
@Override
public boolean isBeforeAdvice() {
return true;
}
@Override
public boolean isAfterAdvice() {
return false;
}
}AbstractAspectJAdvice类实现了 invokeAdviceMethod方法
/**
* Invoke the advice method.
* @param jpMatch the JoinPointMatch that matched this execution join point
* @param returnValue the return value from the method execution (may be null)
* @param ex the exception thrown by the method execution (may be null)
* @return the invocation result
* @throws Throwable in case of invocation failure
*/
protected Object invokeAdviceMethod(
@Nullable JoinPointMatch jpMatch, @Nullable Object returnValue, @Nullable Throwable ex)
throws Throwable {
return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}
// As above, but in this case we are given the join point.
protected Object invokeAdviceMethod(JoinPoint jp, @Nullable JoinPointMatch jpMatch,
@Nullable Object returnValue, @Nullable Throwable t) throws Throwable {
return invokeAdviceMethodWithGivenArgs(argBinding(jp, jpMatch, returnValue, t));
}
protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
Object[] actualArgs = args;
if (this.aspectJAdviceMethod.getParameterCount() == 0) {
actualArgs = null;
}
try {
ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
// TODO AopUtils.invokeJoinpointUsingReflection
return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
}
catch (IllegalArgumentException ex) {
throw new AopInvocationException("Mismatch on arguments to advice method [" +
this.aspectJAdviceMethod + "]; pointcut expression [" +
this.pointcut.getPointcutExpression() + "]", ex);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}invokeAdviceMethodWithGivenArgs方法里面 对apectJAdviceMethod
this.aspectJAdviceMethod.invoke方法 对上面的前置方法进行了调用2、AspectJAfterAdvice 后置增强
前置增强大致结构是 在拦截器链中防止 MethodBeforeAdviceInterceptor,而在MethodBeforeAdviceInterceptor中又防止了AspectJMethodBeforeAdvice,然后调用invoke(相当于用了中间的MethodBeforeAdviceInterceptor 适配器)
而后置增强 没有提供中间的类,直接在拦截器链中使用中间的AspectJAfterAdvice类
/**
* Spring AOP advice wrapping an AspectJ after advice method.
*
* @author Rod Johnson
* @since 2.0
*/
@SuppressWarnings("serial")
public class AspectJAfterAdvice extends AbstractAspectJAdvice
implements MethodInterceptor, AfterAdvice, Serializable {
public AspectJAfterAdvice(
Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {
super(aspectJBeforeAdviceMethod, pointcut, aif);
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
try {
return mi.proceed();
}
finally {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
@Override
public boolean isBeforeAdvice() {
return false;
}
@Override
public boolean isAfterAdvice() {
return true;
}
}
项目中 调用目标方法时
大致流程是:
1、 调用 JdkDynamicAopProxy类的invoke方法
2、获取拦截器链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
3、执行ReflectiveMethodInvocation中的proceed()方法
4、执行拦截器里面的invoke()方法 如:AspectJAfterAdvice 后置通知里面的invoke 方法
那什么时候调用JdkDynamicAopProxy类的invoke方法呢？
class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable{}
InvocationHandler是JDK定义的反射类的一个接口，这个接口定义了invoke方法，而这个invoke方法是作为JDKProxy代理对象进行拦截的回调入口出现的，JdkDynamicAopProxy实现了InvocationHandler接口，也就是说当Proxy对象的代理方法被调用时，JdkDynamicAopProxy的invoke方法作为Proxy对象的回调函数而被触发，从而通过invoke的具体实现，来完成对目标对象方法调用的拦截或者说功能增强的工作
invoke方法是怎么调用的？
动态代理源码分析Proxy类
public class Proxy implements java.io.Serializable 类 实现
Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();////获取安全管理器，安全管理器用于对外部资源的访问控制
//获取安全管理器以及检查是否具有访问权限的过程。安全管理器可能在实际中不太常用，它是为了程序在某些敏感资源的访问上做的权限控制，也就是起到保护程序的作用
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
//1.2检查是否有访问权限//例如：有的程序不允许你对类进行代理，此时加入安全管理器即可防止你对该类的代理。 } /* * Look up or generate the designated proxy class. */ Class<?> cl = getProxyClass0(loader, intfs); /* * Invoke its constructor with the designated invocation handler. */ try { if (sm != null) { checkNewProxyPermission(Reflection.getCallerClass(), cl);//
//检查的是生成的代理类型做权限检查 } final Constructor<?> cons = cl.getConstructor(constructorParams);//
//cl是代理类型其构造器的参数类型为InvocationHandler，所以参数传入InvocationHandler
/
/因为proxy类构造函数是protected Proxy(InvocationHandler h) {}
所以类型是
InvocationHandler final InvocationHandler ih = h; if (!Modifier.isPublic(cl.getModifiers())) { AccessController.doPrivileged(new PrivilegedAction<Void>() { public Void run() { cons.setAccessible(true); return null; } }); }//这里是数组 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); } }
/** * Generate a proxy class. Must call the checkProxyAccess method * to perform permission checks before calling this. */ private static Class<?> getProxyClass0(ClassLoader loader, Class<?>... interfaces) { if (interfaces.length > 65535) { throw new IllegalArgumentException("interface limit exceeded"); } // If the proxy class defined by the given loader implementing // the given interfaces exists, this will simply return the cached copy; // otherwise, it will create the proxy class via the ProxyClassFactory return proxyClassCache.get(loader, interfaces); //从缓存中获取，如果缓存中没有就通过ProxyClassFactory创建 }
/**
* 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);
}
}
}
}
在WeakCache的内部类Factory中 完成了supplier.get()的实现
private final class Factory implements Supplier<V> {
private final K key;
private final P parameter;
private final Object subKey;
private final ConcurrentMap<Object, Supplier<V>> valuesMap;
Factory(K key, P parameter, Object subKey,
ConcurrentMap<Object, Supplier<V>> valuesMap) {
this.key = key;
this.parameter = parameter;
this.subKey = subKey;
this.valuesMap = valuesMap;
}
@Override
public synchronized V get() { // serialize access
// re-check
Supplier<V> supplier = valuesMap.get(subKey);
if (supplier != this) {
// something changed while we were waiting:
// might be that we were replaced by a CacheValue
// or were removed because of failure ->
// return null to signal WeakCache.get() to retry
// the loop
return null;
}
// else still us (supplier == this)
// create new value
V value = null;
try {
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
} finally {
if (value == null) { // remove us on failure
valuesMap.remove(subKey, this);
}
}
// the only path to reach here is with non-null value
assert value != null;
// wrap value with CacheValue (WeakReference)
CacheValue<V> cacheValue = new CacheValue<>(value);
// try replacing us with CacheValue (this should always succeed)
if (valuesMap.replace(subKey, this, cacheValue)) {
// put also in reverseMap
reverseMap.put(cacheValue, Boolean.TRUE);
} else {
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return value;
}
}
然后在实现里面有一个valueFactory.apply(key, parameter)方法，该方法的实现在Proxy的内部类ProxyClassFactory中
然后再到ProxyGenerator.generateProxyClass(proxyName, interfaces, accessFlags)
然后里面有一个 final byte[] classFile = gen.generateClassFile();方法用来生成字节码
最后在生成的字节码文件$Proxy0 里面就可以看到
Method m3;
public final int test(Object paramObject)
throws
{
try
{
return ((Integer)this.h.invoke(this, m3, new Object[] { paramObject })).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
我们在接口中定义的方法test通过反射得到的名字是m3,这里调用代理对象的test方法，
直接就调用了InvocationHandler中的invoke方法，并把m3传了进去。
this.h.invoke(this, m3, null);
这invoke方法是怎么调用的部分参考了https://www.jianshu.com/p/9d5ef621f2d1
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