package common;

public class Test {
  static interface Subject{
    void sayHi();
    void sayHello();
  }

  static class SubjectImpl implements Subject{

    @Override
    public void sayHi() {
      System.out.println("hi");
    }

    @Override
    public void sayHello() {
      System.out.println("hello");
    }
  }

  static class SubjectImplProxy implements Subject{
    private Subject target;

    public SubjectImplProxy(Subject target) {
      this.target=target;
    }

    @Override
    public void sayHi() {
      System.out.print("say:");
      target.sayHi();
    }

    @Override
    public void sayHello() {
      System.out.print("say:");
      target.sayHello();
    }
  }

  public static void main(String[] args) {
    Subject subject=new SubjectImpl();
    Subject subjectProxy=new SubjectImplProxy(subject);
    subjectProxy.sayHi();
    subjectProxy.sayHello();
  }
}

package common;

import java.lang.invoke.MethodHandle;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class Test {
  static interface Subject{
    void sayHi();
    void sayHello();
  }

  static class SubjectImpl implements Subject{

    @Override
    public void sayHi() {
      System.out.println("hi");
    }

    @Override
    public void sayHello() {
      System.out.println("hello");
    }
  }

  static class ProxyInvocationHandler implements InvocationHandler{
    private Subject target;
    public ProxyInvocationHandler(Subject target) {
      this.target=target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      System.out.print("say:");
      return method.invoke(target, args);
    }

  }

  public static void main(String[] args) {
    Subject subject=new SubjectImpl();
    Subject subjectProxy=(Subject) Proxy.newProxyInstance(subject.getClass().getClassLoader(), subject.getClass().getInterfaces(), new ProxyInvocationHandler(subject));
    subjectProxy.sayHi();
    subjectProxy.sayHello();

  }
}

  public static Object newProxyInstance(ClassLoader loader,
                     Class<?>[] interfaces,
                     InvocationHandler h)
    throws IllegalArgumentException
  {
    if (h == null) {
      throw new NullPointerException();
    }

    /*
     * Look up or generate the designated proxy class.
     */
    Class<?> cl = getProxyClass(loader, interfaces);　　//獲取代理類的Class

    /*
     * Invoke its constructor with the designated invocation handler.
     */
    try {
      Constructor cons = cl.getConstructor(constructorParams);　　//constructorParams是寫死的：{ InvocationHandler.class }，上邊返回的代理類Class一定是extends Proxy的，而Proxy有一個參數為InvocationHandler的構造函數
      return cons.newInstance(new Object[] { h });　　//這里通過構造函數將我們自己定義的InvocationHandler的子類傳到代理類的實例里，當我們調用代理類的任何方法時，實際上都會調用我們定義的InvocationHandler子類重寫的invoke()函數
    } catch (NoSuchMethodException e) {
      throw new InternalError(e.toString());
    } catch (IllegalAccessException e) {
      throw new InternalError(e.toString());
    } catch (InstantiationException e) {
      throw new InternalError(e.toString());
    } catch (InvocationTargetException e) {
      throw new InternalError(e.toString());
    }
  }

public static Class<?> getProxyClass(ClassLoader loader,
                     Class<?>... interfaces)
    throws IllegalArgumentException
  {
    if (interfaces.length > 65535) {　　//因為在class文件中，一個類保存的接口數量是用2個字節(jié)來表示的，因此java中一個類最多可以實現65535個接口
      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<Class<?>> interfaceSet = new HashSet<>();
　　　　 //驗證interfaces里的接口是否能被類加載器加載，是否是接口，是否有重復的　
    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<String> key = Arrays.asList(interfaceNames);　　//使用interfaces列表作為key緩存在cache里，也就是實現了相同interfaces的代理類只會創(chuàng)建加載一次

    /*
     * Find or create the proxy class cache for the class loader.
     */
    Map<List<String>, 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.
     */
　　　　 //看看緩存里有沒有，如果有就直接取出來然后return，否則判斷根據pendingGenerationMarker判斷是否有其它線程正在生成當前的代理類，如果有則cache.wait()等待，如果沒有則創(chuàng)建。
    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);
    }
　　　　 //確認要生成的代理類所屬的包，如果interfaces里所有接口都是public的，代理類所屬包就是默認包；如果有interface不是public，那么所有不是public的interface必須在一個包里否則報錯。
    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,
        proxyPkg = "";     // use the unnamed package
      }

      {
        /*
         * Choose a name for the proxy class to generate.
         */
        long num;
        synchronized (nextUniqueNumberLock) {
          num = nextUniqueNumber++;
        }
        String proxyName = proxyPkg + proxyClassNamePrefix + num;　　//生成代理類的名字，proxyPkg是上面確定下來的代理類所在的包名，proxyClassNamePrefix是寫死的字符串“$Proxy”，num是一個全局唯一的long型數字，從0開始累積，每次生成新的代理類就+1，從這里也能看出生成的動態(tài)代理類的數量不能超過Long.maxValue
        /*
         * 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);　　//生成一個以proxyName為類名的，實現了Interfaces里所有接口的類的字節(jié)碼
        try {
          proxyClass = defineClass0(loader, proxyName,
            proxyClassFile, 0, proxyClassFile.length);　　//加載生成的類
        } 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.
       */
　　　　　　　//創(chuàng)建成功，則將cache中該key的pendingGenerationMarker替換為實際的代理類的弱引用，否則也要清除pendingGenerationMarker標記；不管是否成功，都要執(zhí)行cache.notifyAll()，讓其它要創(chuàng)建相同代理類并且執(zhí)行了cache.wait()的線程恢復執(zhí)行。
      synchronized (cache) {
        if (proxyClass != null) {
          cache.put(key, new WeakReference<Class<?>>(proxyClass));
        } else {
          cache.remove(key);
        }
        cache.notifyAll();
      }
    }
    return proxyClass; //最后返回代理類Class
  }

package common;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0 extends Proxy
 implements Test.Subject
{
 private static Method m4;
 private static Method m1;
 private static Method m3;
 private static Method m0;
 private static Method m2;

 static
 {
   try {
     m4 = Class.forName("Test$Subject").getMethod("sayHello", new Class[0]);
     m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
     m3 = Class.forName("Test$Subject").getMethod("sayHi", new Class[0]);
     m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
     m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
  } catch (Exception e) {
    throw new RuntimeException(e);
  }
 }

 public $Proxy0(InvocationHandler paramInvocationHandler)
 {
  super(paramInvocationHandler);
 }

 public final void sayHello()
 {
  try
  {
   this.h.invoke(this, m4, null);
   return;
  }
  catch (RuntimeException localRuntimeException)
  {
   throw localRuntimeException;
  }
  catch (Throwable localThrowable)
  {
    throw new UndeclaredThrowableException(localThrowable);
  }
 }

 public final boolean equals(Object paramObject)
 {
  try
  {
   return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
  }
  catch (RuntimeException localRuntimeException)
  {
   throw localRuntimeException;
  }
  catch (Throwable localThrowable)
  {
    throw new UndeclaredThrowableException(localThrowable);
  }
 }

 public final void sayHi()
 {
  try
  {
   this.h.invoke(this, m3, null);
   return;
  }
  catch (RuntimeException localRuntimeException)
  {
   throw localRuntimeException;
  }
  catch (Throwable localThrowable)
  {
    throw new UndeclaredThrowableException(localThrowable);
  }
 }

 public final int hashCode()
 {
  try
  {
   return ((Integer)this.h.invoke(this, m0, null)).intValue();
  }
  catch (RuntimeException localRuntimeException)
  {
   throw localRuntimeException;
  }
  catch (Throwable localThrowable)
  {
    throw new UndeclaredThrowableException(localThrowable);
  }
 }

 public final String toString()
 {
  try
  {
   return (String)this.h.invoke(this, m2, null);
  }
  catch (RuntimeException localRuntimeException)
  {
   throw localRuntimeException;
  }
  catch (Throwable localThrowable)
  {
    throw new UndeclaredThrowableException(localThrowable);
  }
 }
}