java动态代理【二】：JDK动态代理的内部原理

public synchronized V get()
    {
		//factory获取
      WeakCache.Supplier localSupplier = (WeakCache.Supplier)this.valuesMap.get(this.subKey);
      if (localSupplier != this)
        return null;
      Object localObject1 = null;
      try
      {
		//调用ProxyClassFactory的apply，返回Class类型为localObject1
        localObject1 = Objects.requireNonNull(WeakCache.this.valueFactory.apply(this.key, this.parameter));
      }
      finally
      {
        if (localObject1 == null)
          this.valuesMap.remove(this.subKey, this);
      }
      assert (localObject1 != null);
      WeakCache.CacheValue localCacheValue = new WeakCache.CacheValue(localObject1);
	  //因为Factory和CacheValue都继承Supplier，故可以将原本指向Factory对象替换成指向CacheValue
      if (this.valuesMap.replace(this.subKey, this, localCacheValue))
		//缓存Class
        WeakCache.this.reverseMap.put(localCacheValue, Boolean.TRUE);
      else
        throw new AssertionError("Should not reach here");
      return localObject1;
    }

 /**
     * A factory function that generates, defines and returns the proxy class given
     * the ClassLoader and array of interfaces.
     */
    private static final class ProxyClassFactory
        implements BiFunction<ClassLoader, Class<?>[], Class<?>>
    {
        // prefix for all proxy class names
        //定义类名前缀
        private static final String proxyClassNamePrefix = "$Proxy";
        // next number to use for generation of unique proxy class names
        //生成类序列号和$Proxy组合成类名
        private static final AtomicLong nextUniqueNumber = new AtomicLong();
        @Override
        public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
            Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
            for (Class<?> intf : interfaces) {
                /*
                 * Verify that the class loader resolves the name of this
                 * interface to the same Class object.
                 */
                //循环获取接口类数组
                Class<?> interfaceClass = null;
                try {
                    加载接口类
                    interfaceClass = Class.forName(intf.getName(), false, loader);
                } 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.
                 */
                //判断是否接口
                if (!interfaceClass.isInterface()) {
                    throw new IllegalArgumentException(
                        interfaceClass.getName() + " is not an interface");
                }
                /*
                 * Verify that this interface is not a duplicate.
                 */
                //判断是否有重复的接口
                if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
                    throw new IllegalArgumentException(
                        "repeated interface: " + interfaceClass.getName());
                }
            }
            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.
             */
            //判断是否存在接口类不是public，存在就使用它的包路径
            for (Class<?> intf : interfaces) {
                int flags = intf.getModifiers();
                if (!Modifier.isPublic(flags)) {
                    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");
                    }
                }
            }
            //使用默认的包路径
            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.
             */
            //获取这次动态代理生成class的序列号
            long num = nextUniqueNumber.getAndIncrement();
            String proxyName = proxyPkg + proxyClassNamePrefix + num;
            /*
             * Generate the specified proxy class.
             */
                    //主要代码，生成ProxyClass的java字节码文件
            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces);
            try {
                //defineClass函数会校验class文件并将class文件加载并返回成Class对象
                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());
            }
        }
    }

 public static void writeToDisk(String path) {   
        byte[] class = ProxyGenerator.generateProxyClass("$Proxy0", Star.class.getInterfaces());  
          
        FileOutputStream out = null;  
          
        try {  
            out = new FileOutputStream(path);  
            out.write(class);  
            out.flush();  
        } catch (Exception e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                out.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

private byte[] generateClassFile()
  {
    //添加hashCode函数字节码
    addProxyMethod(hashCodeMethod, Object.class);
    //添加equals函数字节码
    addProxyMethod(equalsMethod, Object.class);
    //添加toString函数字节码
    addProxyMethod(toStringMethod, Object.class);
    //循环添加接口的方法字节码，存储到名为ProxyMethods的Map中，其Key(String)是方法的字符串如
    //java/io/PrintStream.println:(Ljava/lang/String;),value是List<ProxyMethod>,
    for (int i = 0; i < this.interfaces.length; i++)
    {
      localObject1 = this.interfaces[i].getMethods();
      for (int k = 0; k < localObject1.length; k++)
        addProxyMethod(localObject1[k], this.interfaces[i]);
    }
    Iterator localIterator1 = this.proxyMethods.values().iterator();
    while (localIterator1.hasNext())
    {
      localObject1 = (List)localIterator1.next();
      //校验List<ProxyMethod>（有可能有函数名相同的函数，来自不同的接口，但返回类不一样）,判断这些返回类中是否有共同的父类，并设置为函数最终返回类型
      checkReturnTypes((List)localObject1);
    }
    Object localObject2;
    try
    {
      //methods存储的是最终要输出到Class的函数
      this.methods.add(generateConstructor());//添加构造器
      localIterator1 = this.proxyMethods.values().iterator();
      while (localIterator1.hasNext())
      {
        
        localObject1 = (List)localIterator1.next();
        Iterator localIterator2 = ((List)localObject1).iterator();
        while (localIterator2.hasNext())
        {
          localObject2 = (ProxyMethod)localIterator2.next();
          //ProxyClass的成员，成员的类型都是反射Method类型
          this.fields.add(new FieldInfo(((ProxyMethod)localObject2).methodFieldName, "Ljava/lang/reflect/Method;", 10));
          //添加方法
          this.methods.add(((ProxyMethod)localObject2).generateMethod());
        }
      }
      //添加静态的初始化模块：static{}
      this.methods.add(generateStaticInitializer());
    }
    catch (IOException localIOException1)
    {
      throw new InternalError("unexpected I/O Exception");
    }
    if (this.methods.size() > 65535)//
      throw new IllegalArgumentException("method limit exceeded");
    if (this.fields.size() > 65535)
      throw new IllegalArgumentException("field limit exceeded");
    //下面是常量池的创建赋值
    this.cp.getClass(dotToSlash(this.className));
    this.cp.getClass("java/lang/reflect/Proxy");
    for (int j = 0; j < this.interfaces.length; j++)
      this.cp.getClass(dotToSlash(this.interfaces[j].getName()));
    this.cp.setReadOnly();
    //最终输出Class文件，如果有兴趣可以去看一下java的字节码结构和含义
    ByteArrayOutputStream localByteArrayOutputStream = new ByteArrayOutputStream();
    Object localObject1 = new DataOutputStream(localByteArrayOutputStream);
    try
    {
      ((DataOutputStream)localObject1).writeInt(-889275714);
      ((DataOutputStream)localObject1).writeShort(0);
      ((DataOutputStream)localObject1).writeShort(49);
      this.cp.write((OutputStream)localObject1);
      ((DataOutputStream)localObject1).writeShort(49);
      ((DataOutputStream)localObject1).writeShort(this.cp.getClass(dotToSlash(this.className)));
      ((DataOutputStream)localObject1).writeShort(this.cp.getClass("java/lang/reflect/Proxy"));
      ((DataOutputStream)localObject1).writeShort(this.interfaces.length);
      for (int m = 0; m < this.interfaces.length; m++)
        ((DataOutputStream)localObject1).writeShort(this.cp.getClass(dotToSlash(this.interfaces[m].getName())));
      ((DataOutputStream)localObject1).writeShort(this.fields.size());
      Iterator localIterator3 = this.fields.iterator();
      while (localIterator3.hasNext())
      {
        localObject2 = (FieldInfo)localIterator3.next();
        ((FieldInfo)localObject2).write((DataOutputStream)localObject1);
      }
      ((DataOutputStream)localObject1).writeShort(this.methods.size());
      localIterator3 = this.methods.iterator();
      while (localIterator3.hasNext())
      {
        localObject2 = (MethodInfo)localIterator3.next();
        ((MethodInfo)localObject2).write((DataOutputStream)localObject1);
      }
      ((DataOutputStream)localObject1).writeShort(0);
    }
    catch (IOException localIOException2)
    {
      throw new InternalError("unexpected I/O Exception");
    }
    return (B)(B)localByteArrayOutputStream.toByteArray();
  }

import cglib.Eat;
import cglib.Speak;
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 Speak, Eat
{
   //对应this.fields.add(new FieldInfo(((ProxyMethod)localObject2).methodFieldName, "Ljava/lang/reflect/Method;", 10));
  private static Method m3;
  private static Method m1;
  private static Method m4;
  private static Method m0;
  private static Method m2;
// 对应this.methods.add(generateConstructor());//添加构造器
 public $Proxy0(InvocationHandler paramInvocationHandler)
    throws 
  {
    super(paramInvocationHandler);
  }
    // 对应this.methods.add(((ProxyMethod)localObject2).generateMethod());
  public final void say()
    throws 
  {
    try
    {
      this.h.invoke(this, m3, null);
      return;
    }
    catch (RuntimeException localRuntimeException)
    {
      throw localRuntimeException;
    }
    catch (Throwable localThrowable)
    {
    }
    throw new UndeclaredThrowableException(localThrowable);
  }
  public final boolean equals(Object paramObject)
    throws 
  {
    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 eat()
    throws 
  {
    try
    {
      this.h.invoke(this, m4, null);
      return;
    }
    catch (RuntimeException localRuntimeException)
    {
      throw localRuntimeException;
    }
    catch (Throwable localThrowable)
    {
    }
    throw new UndeclaredThrowableException(localThrowable);
  }
  public final int hashCode()
    throws 
  {
    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()
    throws 
  {
    try
    {
      return (String)this.h.invoke(this, m2, null);
    }
    catch (RuntimeException localRuntimeException)
    {
      throw localRuntimeException;
    }
    catch (Throwable localThrowable)
    {
    }
    throw new UndeclaredThrowableException(localThrowable);
  }
  //对应this.methods.add(generateStaticInitializer());
  static
  {
    try
    {
      m3 = Class.forName("cglib.Speak").getMethod("say", new Class[0]);
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m4 = Class.forName("cglib.Eat").getMethod("eat", 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]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
    }
    throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
  }
}