接上一篇代理（Proxy）模式，看下proxy内部到底做了什么处理。通过上篇的代码debug，如图
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发现这里调用proxy发现如下图中的$Proxy0和$Proxy1代理类，如何来的呢？先回顾一些知识：
类的完整生命周期如图：
一般类的完整生命周期从源文件开始，然后通过javac编译成字节码文件，然后通过类加载机制在元空间（1.7之前为方法区）生成class对象，然后new出实例化对象在堆中，之后通过可达性分析判断类是否还在被引用，没有引用在被垃圾回收GC回收。完整的生命周期。为啥在动态代理中谈到这个类的生命周期，其实所谓的$Proxy0和$Proxy1变量的生成就是跳过了源文件的编译直接从内存中生成的字节码。
接下来我们去看看源码，里面到底是如何在内存中生成字节码文件的。首先看到之前的getProxyInstance()方法：
进入看看源码：
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();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
*/
//******动态代理的核心方法
//*******JVM直接在内存中生成字节码文件并通过类加载机制得到class对象，对比类的生命周期
Class<?> cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
//**********通过class对象拿到目标对象的构造方法*************
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;
}
});
}
//**********通过反射得到类的实例对象*************
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);
}
}注解加入了//***的注解，核心代码还是getProxyClass0()方法。继续往里深入，
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
return proxyClassCache.get(loader, interfaces); //继续往下
}进入get（）方法：
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
//***************************优先从缓存里面去生成代理类******************************
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
//***************************如果从缓存中没有拿到代理类，就去生成代理类******************************
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));}
继续深入apply（）：真正的核心到了。
// prefix for all proxy class names
private static final String proxyClassNamePrefix = "$Proxy"; //前缀 @Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class<?> intf : interfaces) { //****判断多少个接口，在我们的例子中就是抽象接口——某激情公司，实现某置定接口
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
Class<?> interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);//****拿到接口的class
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " 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.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}
String proxyPkg = null; // package to define proxy class in
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* 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 (Class<?> intf : interfaces) { //判断接口里面是不是加了public修饰符
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) {
accessFlags = Modifier.FINAL;
String name = intf.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 = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num; //为什么会出现动态代理类$Proxy0和$Proxy1
/*
* Generate the specified proxy class.
*/
//获取到代理类的字节码（内存中直接生成class文件）
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
//把字节码，类名，类加载器丢进去拿到class对象（对应类周期的两步骤）defineClass0是一个native方法
return 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());
}
}
}内存中代理类的内部生成就到这里了。
之后对生成的代理类进行反编译工具，看到代理类都是Proxy的子类，代理类都要继承Porxy以及实现指定的接口。重写的方法里面调用相关业务方法的时候，调用this.h.invoke()，h->>InvocationHandler，所以就是调用动态代理类PassionProxyCompany中的invoke方法（通过动态代理对象对方法进行增强）。
动态代理类的生成核心代码基本如上了，搞清楚一个问题看源码的确不容易。继续加油把。。。。
