摘要：序论整个，是其中的基石之一，而动态代理是的基础。这里主要摘录下基于接口的动态代理的源码，备忘。
序
论整个J2EE，aop是其中的基石之一，而动态代理是aop的基础。这里主要摘录下jdk基于接口的动态代理的源码，备忘。
Proxy.newProxyInstance/**
* Returns an instance of a proxy class for the specified interfaces
* that dispatches method invocations to the specified invocation
* handler. This method is equivalent to:
*
* Proxy.getProxyClass(loader, interfaces).
* getConstructor(new Class[] { InvocationHandler.class }).
* newInstance(new Object[] { handler });
*
*
* {@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 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
{
if (h == null) {
throw new NullPointerException();
}
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, interfaces);
}
/*
* Look up or generate the designated proxy class.
*/
Class cl = getProxyClass0(loader, interfaces);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
final Constructor cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
// create proxy instance with doPrivilege as the proxy class may
// implement non-public interfaces that requires a special permission
return AccessController.doPrivileged(new PrivilegedAction
getProxyClass0
/**
* 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");
}
Class proxyClass = null;
/* collect interface names to use as key for proxy class cache */
String[] interfaceNames = new String[interfaces.length];
// for detecting duplicates
Set> interfaceSet = new HashSet<>();
for (int i = 0; i < interfaces.length; i++) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
String interfaceName = interfaces[i].getName();
Class interfaceClass = null;
try {
interfaceClass = Class.forName(interfaceName, false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != interfaces[i]) {
throw new IllegalArgumentException(
interfaces[i] + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
if (interfaceSet.contains(interfaceClass)) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
interfaceSet.add(interfaceClass);
interfaceNames[i] = interfaceName;
}
/*
* Using string representations of the proxy interfaces as
* keys in the proxy class cache (instead of their Class
* objects) is sufficient because we require the proxy
* interfaces to be resolvable by name through the supplied
* class loader, and it has the advantage that using a string
* representation of a class makes for an implicit weak
* reference to the class.
*/
List key = Arrays.asList(interfaceNames);
/*
* Find or create the proxy class cache for the class loader.
*/
Map, Object> cache;
synchronized (loaderToCache) {
cache = loaderToCache.get(loader);
if (cache == null) {
cache = new HashMap<>();
loaderToCache.put(loader, cache);
}
/*
* This mapping will remain valid for the duration of this
* method, without further synchronization, because the mapping
* will only be removed if the class loader becomes unreachable.
*/
}
/*
* Look up the list of interfaces in the proxy class cache using
* the key. This lookup will result in one of three possible
* kinds of values:
* null, if there is currently no proxy class for the list of
* interfaces in the class loader,
* the pendingGenerationMarker object, if a proxy class for the
* list of interfaces is currently being generated,
* or a weak reference to a Class object, if a proxy class for
* the list of interfaces has already been generated.
*/
synchronized (cache) {
/*
* Note that we need not worry about reaping the cache for
* entries with cleared weak references because if a proxy class
* has been garbage collected, its class loader will have been
* garbage collected as well, so the entire cache will be reaped
* from the loaderToCache map.
*/
do {
Object value = cache.get(key);
if (value instanceof Reference) {
proxyClass = (Class) ((Reference) value).get();
}
if (proxyClass != null) {
// proxy class already generated: return it
return proxyClass;
} else if (value == pendingGenerationMarker) {
// proxy class being generated: wait for it
try {
cache.wait();
} catch (InterruptedException e) {
/*
* The class generation that we are waiting for should
* take a small, bounded time, so we can safely ignore
* thread interrupts here.
*/
}
continue;
} else {
/*
* No proxy class for this list of interfaces has been
* generated or is being generated, so we will go and
* generate it now. Mark it as pending generation.
*/
cache.put(key, pendingGenerationMarker);
break;
}
} while (true);
}
try {
String proxyPkg = null; // package to define proxy class in
/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package. Verify that
* all non-public proxy interfaces are in the same package.
*/
for (int i = 0; i < interfaces.length; i++) {
int flags = interfaces[i].getModifiers();
if (!Modifier.isPublic(flags)) {
String name = interfaces[i].getName();
int n = name.lastIndexOf(".");
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) {
// if no non-public proxy interfaces, use com.sun.proxy package
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}
{
/*
* Choose a name for the proxy class to generate.
*/
long num;
synchronized (nextUniqueNumberLock) {
num = nextUniqueNumber++;
}
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Verify that the class loader hasn"t already
* defined a class with the chosen name.
*/
/*
* Generate the specified proxy class.
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces);
try {
proxyClass = defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
// add to set of all generated proxy classes, for isProxyClass
proxyClasses.put(proxyClass, null);
} finally {
/*
* We must clean up the "pending generation" state of the proxy
* class cache entry somehow. If a proxy class was successfully
* generated, store it in the cache (with a weak reference);
* otherwise, remove the reserved entry. In all cases, notify
* all waiters on reserved entries in this cache.
*/
synchronized (cache) {
if (proxyClass != null) {
cache.put(key, new WeakReference>(proxyClass));
} else {
cache.remove(key);
}
cache.notifyAll();
}
}
return proxyClass;
}
newInstance
private static Object newInstance(Constructor cons, InvocationHandler h) {
try {
return cons.newInstance(new Object[] {h} );
} catch (IllegalAccessException | InstantiationException e) {
throw new InternalError(e.toString());
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString());
}
}
}
文章版权归作者所有，未经允许请勿转载,若此文章存在违规行为，您可以联系管理员删除。
转载请注明本文地址：https://www.ucloud.cn/yun/65750.html
摘要：值得一提的是由于采用动态创建子类的方式生成代理对象，所以不能对目标类中的方法进行代理。动态代理中生成的代理类是子类，调试的时候可以看到，打开源码可看到实现了和也就实现方法。 前面讲到了动态代理的底层原理，接下来我们来看一下aop的动态代理.Spring AOP使用了两种代理机制：一种是基于JDK的动态代理，一种是基于CGLib的动态代理. ①JDK动态代理：使用JDK创建代理有一个限制...
摘要：总结动态代理的相关原理已经讲解完毕，接下来让我们回答以下几个思考题。 【干货点】 此处是【好好面试】系列文的第12篇文章。文章目标主要是通过原理剖析的方式解答Aop动态代理的面试热点问题，通过一步步提出问题和了解原理的方式，我们可以记得更深更牢，进而解决被面试官卡住喉咙的情况。问题如下 SpringBoot默认代理类型是什么 为什么不用静态代理 JDK动态代理原理 CGLIB动态代理...
摘要：最近公司内部系统相互通信调用用到了的机制后来有空研究了一下的机制在这里做一个简单的摘要有不对的地方希望指正首先看客户端的基础类他是一个工厂意味着他具有包装的功能当你调用的的的方法返回的并不是他本身而是被他包装过得下图的箭头及包装的地方实际上 最近公司内部系统相互通信调用用到了spring的hessian机制,后来有空研究了一下spring hessian的机制,在这里做一个简单的摘要,...
摘要：，，面向切面编程。，切点，切面匹配连接点的点，一般与切点表达式相关，就是切面如何切点。例子中，注解就是切点表达式，匹配对应的连接点，通知，指在切面的某个特定的连接点上执行的动作。，织入，将作用在的过程。因为源码都是英文写的。 之前《零基础带你看Spring源码——IOC控制反转》详细讲了Spring容器的初始化和加载的原理，后面《你真的完全了解Java动态代理吗？看这篇就够了》介绍了下...
摘要：与静态代理对比，动态代理是在动态生成代理类，由代理类完成对具体方法的封装，实现的功能。本文将分析中两种动态代理的实现方式，和，比较它们的异同。那如何动态编译呢你可以使用，这是一个封装了的库，帮助你方便地实现动态编译源代码。 发现Java面试很喜欢问Spring AOP怎么实现的之类的问题，所以写一篇文章来整理一下。关于AOP和代理模式的概念这里并不做赘述，而是直奔主题，即AOP的实现方...
阅读 1097·2021-09-27 13:35
阅读 2316·2021-09-06 15:12
阅读 3164·2019-08-30 15:55
阅读 2717·2019-08-30 15:43
阅读 302·2019-08-29 16:42
阅读 3292·2019-08-29 15:39
阅读 2964·2019-08-29 12:28
阅读 1116·2019-08-29 11:11
