关于Java的动态代理机制

interface IFunction {
	void doAThing();
}

class FunctionProvider implement IFunction {
	public void doAThing {
		System.out.print("do A");
	}
}

class Proxy implement IFunction {
	private FunctionProvider provider;
	Proxy(FunctionProvider provider) {
		this.provider = provider;
	}
	public void doAThing {
		provider.doAThing();
	}
}

interface IAFunc {
	void doA();
}
interface IBFunc {
	void doB();
}
class TimeConsumeProxy implement IAFunc, IBFunc {
	private AFunc a;
	private BFunc b;
	public(AFunc a, BFunc b) {
		this.a = a;
		this.b = b;
	}
	void doA() {
		long start = System.currentMillions();
		a.doA();
		System.out.println("耗时：" + (System.currentMillions() - start));
	}
	void doB() {
		long start = System.currentMillions();
		b.doB();
		System.out.println("耗时：" + (System.currentMillions() - start));
	}
}

interface IAFunc {
	void doA();
}
interface IBFunc {
	void doB();
}
class A implement IAFunc { ... }
class B implement IBFunc { ... }
class TimeConsumeProxy implements InvocationHandler {
	private Object realObject;
	public Object bind(Object realObject) {
		this.realObject = realObject;
		Object proxyObject = Proxy.newInstance(
			realObject.getClass().getClassLoader(),
			realObject.getClass().getInterfaces(),
			this
		);
		return proxyObject;
	}
	@Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        long start = System.currentMillions();
        Object result = method.invoke(target, args);
        System.out.println("耗时：" + (System.currentMillions() - start));
        return result;
    }
}

public static void main(String[] args) {
	A a = new A();
	IAFunc aProxy = (IAFunc) new TimeConsumeProxy().bind(a);
	aProxy.doA();
	B b = new B();
	IBFunc bProxy = (IBFunc) new TimeConsumeProxy().bind(b);
	bProxy.doB();	
}

Object proxyObject = Proxy.newInstance(
			realObject.getClass().getClassLoader(),
			realObject.getClass().getInterfaces(),
			this
		);

IAFunc aProxy = (IAFunc) new TimeConsumeProxy().bind(a);
aProxy.doA();

final class $Proxy0 extends Proxy implements IAFunc {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;
    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }
    public final boolean equals(Object var1) throws  {
        // 省略
    }
    public final void doA() throws  {
        try {
        	// 划重点
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }
    public final String toString() throws  {
        // 省略
    }
    public final int hashCode() throws  {
        // 省略
    }
    static {
        try {
        	// 划重点
            m3 = Class.forName("proxy.IAFunc").getMethod("doA", new Class[0]);
            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

super.h.invoke(this, m3, (Object[])null);

public Object invoke(Object proxy, Method method, Object[] args);

IAFunc aProxy = (IAFunc) new TimeConsumeProxy().bind(a);aProxy.doA();

Object proxyObject = Proxy.newInstance(
			realObject.getClass().getClassLoader(),
			realObject.getClass().getInterfaces(),
			this
		);

public static Object newProxyInstance(ClassLoader loader,
                                      Class<?>[] interfaces,
                                      InvocationHandler h) {
    // 复制要代理的接口                                  	
	final Class<?>[] intfs = interfaces.clone();
	// 重点：生成 $Proxy0.class 文件并通过 ClassLoader 加载进来
	Class<?> cl = getProxyClass0(loader, intfs);
	// 对 $Proxy0.class 生成一个实例，就是 `proxyObject`
	final Constructor<?> cons = cl.getConstructor(constructorParams);
	return cons.newInstance(new Object[]{h});
}

@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
	// 参数为 ClassLoader 和要代理的接口
	Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
	// 1. 验证 ClassLoader 和接口有效性
	for (Class<?> intf : interfaces) {
		// 验证 classLoader 正确性
		Class<?> interfaceClass = Class.forName(intf.getName(), false, loader);
		if (interfaceClass != intf) {
            throw new IllegalArgumentException(
                intf + " is not visible from class loader");
        }
		// 验证传入的接口 class 有效
		if (!interfaceClass.isInterface()) { ... } 
		// 验证接口是否重复
		if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) { ... }
	}
	// 2. 创建包名及类名 $Proxy0.class
	proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
	long num = nextUniqueNumber.getAndIncrement();
    String proxyName = proxyPkg + proxyClassNamePrefix + num;
    // 3. 创建 class 字节码内容
    byte[] proxyClassFile = ProxyGenerator.generateProxyClass(proxyName, interfaces, accessFlags);
    // 4. 基于字节码和类名，生成 Class<?> 对象
    return defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length);
}

// 添加 hashCode equals toString 方法
addProxyMethod(hashCodeMethod, Object.class);
addProxyMethod(equalsMethod, Object.class);
addProxyMethod(toStringMethod, Object.class);
// 添加委托类的接口实现
for (int i = 0; i < interfaces.length; i++) {
    Method[] methods = interfaces[i].getMethods();
    for (int j = 0; j < methods.length; j++) {
         addProxyMethod(methods[j], interfaces[i]);
    }
}
// 添加构造函数
methods.add(this.generateConstructor());

ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(bout);
dout.writeInt(0xCAFEBABE);
...
dout.writeShort(ACC_PUBLIC | ACC_FINAL | ACC_SUPER);
...
return bout.toByteArray();