SPRING 阅读--JdkDynamicAopProxy
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(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false; // 通过this.advised得到代理的目标类,
TargetSource targetSource = this.advised.targetSource;
Object target = null; try {
// 如何代理接口没有定义equals方法,则调用JdkDynamicAopProxy的重写的equals方法
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
// 如何代理接口没有定义equals方法,则调用JdkDynamicAopProxy的重写的equals方法
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
//如果该方法申明类是DecoratingProxy,则直接最终的被代理类的类Class
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
//如果目标对象是Advice类型,则直接使用反射进行调用
//opaque-->标记是否需要阻止通过该配置创建的代理对象转换为Advised类型,默认值为false,表示代理对象可以被转换为Advised类型 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;
// 看是否需要暴露代理对象,如果需要放到threadLocal上
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); // 得到该调用方法的拦截链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass); // Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
// 如果拦截链为空,直接返回调到该方法
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.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// 否则创建 MethodInvocation 执行拦截调用
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed();
} // Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
// 如果返回值是this,那么返回值替换为代理对象,而不是原对象。
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);
}
}
}
static Class<?>[] completeProxiedInterfaces(AdvisedSupport advised, boolean decoratingProxy) {
Class<?>[] specifiedInterfaces = advised.getProxiedInterfaces();
// 首先得到用户设置的代理接口,如果没有检查和设置代理类是否是一个接口
if (specifiedInterfaces.length == 0) {
// No user-specified interfaces: check whether target class is an interface.
Class<?> targetClass = advised.getTargetClass();
if (targetClass != null) {
if (targetClass.isInterface()) {
advised.setInterfaces(targetClass);
}
else if (Proxy.isProxyClass(targetClass)) {
advised.setInterfaces(targetClass.getInterfaces());
}
specifiedInterfaces = advised.getProxiedInterfaces();
}
}
// 如果用户代理的接口设置中没有SpringProxy接口,需要把代理类实现SpringProxy接口,该接口是个标记接口,说明是Spring代理
boolean addSpringProxy = !advised.isInterfaceProxied(SpringProxy.class);
// 如果代理类可以转化为Advised类型,并且用户没有指定Advised,则添加该接口,
//所以这里可以知道一般Spring的代理类都实现了该Advised接口
boolean addAdvised = !advised.isOpaque() && !advised.isInterfaceProxied(Advised.class);
//如果decoratingProxy==true,并且用户未添加DecoratingProxy接口,则代理需要实现该接口DecoratingProxy
boolean addDecoratingProxy = (decoratingProxy && !advised.isInterfaceProxied(DecoratingProxy.class));
int nonUserIfcCount = 0;
if (addSpringProxy) {
nonUserIfcCount++;
}
if (addAdvised) {
nonUserIfcCount++;
}
if (addDecoratingProxy) {
nonUserIfcCount++;
}
Class<?>[] proxiedInterfaces = new Class<?>[specifiedInterfaces.length + nonUserIfcCount];
System.arraycopy(specifiedInterfaces, 0, proxiedInterfaces, 0, specifiedInterfaces.length);
int index = specifiedInterfaces.length;
if (addSpringProxy) {
proxiedInterfaces[index] = SpringProxy.class;
index++;
}
if (addAdvised) {
proxiedInterfaces[index] = Advised.class;
index++;
}
if (addDecoratingProxy) {
proxiedInterfaces[index] = DecoratingProxy.class;
}
// 所以从上面分析得知,proxiedInterfaces会返回用户制定的代理接口+SpringProxy、Advised、DecoratingProxy
return proxiedInterfaces;
}
public interface Human {
Human getInstance();
}
public class ChineseHuman implements Human { private String desc; public ChineseHuman() {
} public ChineseHuman(String desc) {
this.desc = desc;
} public String getDesc() {
return desc;
} public void setDesc(String desc) {
this.desc = desc;
} @Override
public Human getInstance() {
System.out.println("human desc:" + desc);
return this;
}
}
public class JdkDynamicAopProxyTests { @Test
public void testJdkProxy() {
AdvisedSupport advisedSupport = new AdvisedSupport();
advisedSupport.setInterfaces(Human.class);
advisedSupport.setTargetSource(new TargetSource() {
@Override
public Class<?> getTargetClass() {
return ChineseHuman.class;
} @Override
public boolean isStatic() {
return false;
} @Override
public Object getTarget() throws Exception {
return new ChineseHuman("中国人");
} @Override
public void releaseTarget(Object target) throws Exception { }
});
JdkDynamicAopProxy jdkDynamicAopProxy = new JdkDynamicAopProxy(advisedSupport); Human human = (Human) Proxy.newProxyInstance(JdkDynamicAopProxy.class.getClassLoader(), new Class[]{Human.class}, jdkDynamicAopProxy); System.out.println(human.getInstance()); // JDK原生代理,必然为true,因为本身是生成的是代理的接口的对象
System.out.println("human instanceof Human:" + (human instanceof Human)); //false
System.out.println("human instanceof ChineseHuman:" + (human instanceof ChineseHuman));
//false
System.out.println("human instanceof Advised:" + (human instanceof Advised));
//false
System.out.println("human instanceof SpringProxy:" + (human instanceof SpringProxy));
//false
System.out.println("human instanceof DecoratingProxy:" + (human instanceof DecoratingProxy));
//true, 有个面试题是这么问的,java动态代理为啥代理是接口,不能是类,
// 其根原在于JDK的动态代理实现方式是代理对象继承了java.lang.reflect.Proxy,并且java单继承,所以无法代理类
System.out.println("human instanceof Proxy:" + (human instanceof Proxy)); System.out.println("Spring JDK代理扩展========="); human = (Human) jdkDynamicAopProxy.getProxy(); System.out.println(human.getInstance()); // 该代理对象的getInstance返回是其本身,原因也在于上面分析的红色部分原因。
System.out.println("human== human.getInstance():" + (human == human.getInstance())); // true
System.out.println("human instanceof Human:" + (human instanceof Human));
//false
System.out.println("human instanceof ChineseHuman:" + (human instanceof ChineseHuman));
//true
System.out.println("human instanceof Advised:" + (human instanceof Advised));
// true
System.out.println("human instanceof SpringProxy:" + (human instanceof SpringProxy));
// true
System.out.println("human instanceof DecoratingProxy:" + (human instanceof DecoratingProxy));
//true
System.out.println("human instanceof Proxy:" + (human instanceof Proxy));
}
}
从上面的测试可以知道,一个对象被Spring的JDK动态代理后,其代理对象会实现其用户指定的代理接口外,还会实现Advised,SpringProxy,DecoratingProxy接口。
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