深度剖析java中JDK动态代理机制

public class MyProxy {

  public interface IHello{

    void sayHello();

  }

  static class Hello implements IHello{

    public void sayHello() {

      System.out.println("Hello world!!");

    }

  }

  //自定义InvocationHandler

  static class HWInvocationHandler implements InvocationHandler{

    //目标对象

    private Object target;

    public HWInvocationHandler(Object target){

      this.target = target;

    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

      System.out.println("------插入前置通知代码-------------");

      //执行相应的目标方法

      Object rs = method.invoke(target,args);

      System.out.println("------插入后置处理代码-------------");

      return rs;

    }

  }

  public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetExc  eption, InstantiationException {

    //生成$Proxy0的class文件

    System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

    //获取动态代理类

    Class proxyClazz = Proxy.getProxyClass(IHello.class.getClassLoader(),IHello.class);

    //获得代理类的构造函数，并传入参数类型InvocationHandler.class

    Constructor constructor = proxyClazz.getConstructor(InvocationHandler.class);

    //通过构造函数来创建动态代理对象，将自定义的InvocationHandler实例传入

    IHello iHello = (IHello) constructor.newInstance(new HWInvocationHandler(new Hello()));

    //通过代理对象调用目标方法

    iHello.sayHello();

  }

} 

public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {

    //生成$Proxy0的class文件

    System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

    IHello ihello = (IHello) Proxy.newProxyInstance(IHello.class.getClassLoader(), //加载接口的类加载器

        new Class[]{IHello.class},   //一组接口

        new HWInvocationHandler(new Hello())); //自定义的InvocationHandler

    ihello.sayHello();

  } 

public static Object newProxyInstance(ClassLoader loader,

                     Class<!--?-->[] interfaces,

                     InvocationHandler h)

      throws IllegalArgumentException

  {

    if (h == null) {  //如果h为空直接抛出异常，所以InvocationHandler实例对象是必须的

      throw new NullPointerException();

    }

    //对象的拷贝,暂不知道这里拷贝下的意义是啥？

    final Class<!--?-->[] intfs = interfaces.clone();

    //一些安全的权限检查

    final SecurityManager sm = System.getSecurityManager();

    if (sm != null) {

      checkProxyAccess(Reflection.getCallerClass(), loader, intfs);

    }

    //产生代理类

    Class<!--?--> cl = getProxyClass0(loader, intfs);

 

    //获取代理类的构造函数对象

    //参数constructorParames为常量值：private static final Class<!--?-->[] constructorParams = { InvocationHandler.class };

    final Constructor<!--?--> cons = cl.getConstructor(constructorParames);

    final InvocationHandler ih = h;

    //根据代理类的构造函数对象来创建代理类对象

    return newInstance(cons, ih);

       

  } 

private static Class<!--?--> getProxyClass0(ClassLoader loader,

                      Class<!--?-->... interfaces) {

//接口数不得超过65535个

    if (interfaces.length > 65535) {

      throw new IllegalArgumentException("interface limit exceeded");

    }

//代理类缓存，如果缓存中有代理类了直接返回，否则将由ProxyClassFactory创建代理类

    return proxyClassCache.get(loader, interfaces);

  } 

private static final class ProxyClassFactory

    implements BiFunction<classloader, class<?="">[], Class<!--?-->>

  {

    //统一代理类的前缀名都以$Proxy开关

    private static final String proxyClassNamePrefix = "$Proxy";

    //使用唯一的编号给作为代理类名的一部分，如$Proxy0,$Proxy1等

    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) {

        //验证指定的类加载器(loader)加载接口所得到的Class对象(interfaceClass)是否与intf对象相同

        Class<!--?--> interfaceClass = null;

        try {

          interfaceClass = Class.forName(intf.getName(), false, loader);

        } catch (ClassNotFoundException e) {

        }

        if (interfaceClass != intf) {

          throw new IllegalArgumentException(

            intf + " is not visible from class loader");

        }

        //验证该Class对象是不是接口

        if (!interfaceClass.isInterface()) {

          throw new IllegalArgumentException(

            interfaceClass.getName() + " is not an interface");

        }

        // 验证该接口是否重复了

        if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {

          throw new IllegalArgumentException(

            "repeated interface: " + interfaceClass.getName());

        }

      }

         //声明代理类所在包

      String proxyPkg = null;  

      /*验证你传入的接口中是否有非public接口，只要有一个接口是非public的，那么这些接口都必须在同一包中

      这里的接口修饰符直接影响到System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true")所生成

      的代理类的路径，往下看！！*/

      for (Class<!--?--> intf : interfaces) {

        int flags = intf.getModifiers();

        if (!Modifier.isPublic(flags)) {

          String name = intf.getName();

          int n = name.lastIndexOf('.');

          //截取完整包名

          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) {

        /*如果都是public接口，那么生成的代理类就在com.sun.proxy包下如果报java.io.FileNotFoundException: com\sun\proxy\$Proxy0.c         lass (系统找不到指定的路径。)的错误，就先在你项目中创建com.sun.proxy路径*/      

        proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";

      }

 

       //将当前nextUniqueNumber的值以原子的方式的加1，所以第一次生成代理类的名字为$Proxy0.class

      long num = nextUniqueNumber.getAndIncrement();

      //代理类的完全限定名，如com.sun.proxy.$Proxy0.calss,

      String proxyName = proxyPkg + proxyClassNamePrefix + num;

      //生成代理类字节码文件       

      byte[] proxyClassFile = ProxyGenerator.generateProxyClass(

        proxyName, interfaces);

      try {

        return defineClass0(loader, proxyName,

                  proxyClassFile, 0, proxyClassFile.length);

      } catch (ClassFormatError e) {

        throw new IllegalArgumentException(e.toString());

      }

    }

  }</class<?></classloader,> 

public static byte[] generateProxyClass(final String var0, Class[] var1) {

    ProxyGenerator var2 = new ProxyGenerator(var0, var1);

    //生成代理类字节码文件的真正方法

    final byte[] var3 = var2.generateClassFile();

    //保存文件

    if(saveGeneratedFiles) {

      AccessController.doPrivileged(new PrivilegedAction() {

        public Void run() {

          try {

            FileOutputStream var1 = new FileOutputStream(ProxyGenerator.dotToSlash(var0) + ".class");

            var1.write(var3);

            var1.close();

            return null;

          } catch (IOException var2) {

            throw new InternalError("I/O exception saving generated file: " + var2);

          }

        }

      });

    }

    return var3;

  } 

private byte[] generateClassFile() {

    /addProxyMethod系列方法就是将接口的方法和Object的hashCode,equals,toString方法添加到代理方法容器(proxyMethods),

     其中方法签名作为key,proxyMethod作为value*/

    /*hashCodeMethod方法位于静态代码块中通过Object对象获得，hashCodeMethod=Object.class.getMethod("hashCode",new Class[0]),

     相当于从Object中继承过来了这三个方法equalsMethod,toStringMethod*/  

    this.addProxyMethod(hashCodeMethod, Object.class);  -->

    this.addProxyMethod(equalsMethod, Object.class);

    this.addProxyMethod(toStringMethod, Object.class);

    int var1;

    int var3;

     //获得所有接口中的所有方法，并将方法添加到代理方法中

    for(var1 = 0; var1 < this.interfaces.length; ++var1) {

      Method[] var2 = this.interfaces[var1].getMethods();      

      for(var3 = 0; var3 < var2.length; ++var3) {

        this.addProxyMethod(var2[var3], this.interfaces[var1]);

      }

    }

     

    Iterator var7 = this.proxyMethods.values().iterator();

    List var8;

    while(var7.hasNext()) {

      var8 = (List)var7.next();

      checkReturnTypes(var8);  //验证具有相同方法签名的的方法的返回值类型是否一致，因为不可能有两个方法名相同,参数相同，而返回值却不同的方法

    };

  //接下来就是写代理类文件的步骤了

    Iterator var11

    try {

       //生成代理类的构造函数

      this.methods.add(this.generateConstructor());

      var7 = this.proxyMethods.values().iterator();

      while(var7.hasNext()) {

        var8 = (List)var7.next();

        var11 = var8.iterator();

        while(var11.hasNext()) {

          ProxyGenerator.ProxyMethod var4 = (ProxyGenerator.ProxyMethod)var11.next();

          /将代理字段声明为Method，10为ACC_PRIVATE和ACC_STATAIC的与运算，表示该字段的修饰符为private static

           所以代理类的字段都是private static Method XXX*/

          this.fields.add(new ProxyGenerator.FieldInfo(var4.methodFieldName, "Ljava/lang/reflect/Method;", 10));

          //生成代理类的代理方法

          this.methods.add(var4.generateMethod());

        }

      }

      //为代理类生成静态代码块，对一些字段进行初始化

      this.methods.add(this.generateStaticInitializer());

    } catch (IOException var6) {

      throw new InternalError("unexpected I/O Exception");

    }

    

    if(this.methods.size() > '\uffff') { //代理方法超过65535将抛出异常

      throw new IllegalArgumentException("method limit exceeded");

    } else if(this.fields.size() > '\uffff') {  //代理类的字段超过65535将抛出异常

      throw new IllegalArgumentException("field limit exceeded");

    } else {

     //这里开始就是一些代理类文件的过程，此过程略过

      this.cp.getClass(dotToSlash(this.className));

      this.cp.getClass("java/lang/reflect/Proxy");

      for(var1 = 0; var1 < this.interfaces.length; ++var1) {

        this.cp.getClass(dotToSlash(this.interfaces[var1].getName()));

      }

      this.cp.setReadOnly();

      ByteArrayOutputStream var9 = new ByteArrayOutputStream();

      DataOutputStream var10 = new DataOutputStream(var9);

      try {

        var10.writeInt(-889275714);

        var10.writeShort(0);

        var10.writeShort(49);

        this.cp.write(var10);

        var10.writeShort(49);

        var10.writeShort(this.cp.getClass(dotToSlash(this.className)));

        var10.writeShort(this.cp.getClass("java/lang/reflect/Proxy"));

        var10.writeShort(this.interfaces.length);

        for(var3 = 0; var3 < this.interfaces.length; ++var3) {

          var10.writeShort(this.cp.getClass(dotToSlash(this.interfaces[var3].getName())));

        }

        var10.writeShort(this.fields.size());

        var11 = this.fields.iterator();

        while(var11.hasNext()) {

          ProxyGenerator.FieldInfo var12 = (ProxyGenerator.FieldInfo)var11.next();

          var12.write(var10);

        }

        var10.writeShort(this.methods.size());

        var11 = this.methods.iterator();

        while(var11.hasNext()) {

          ProxyGenerator.MethodInfo var13 = (ProxyGenerator.MethodInfo)var11.next();

          var13.write(var10);

        }

        var10.writeShort(0);

        return var9.toByteArray();

      } catch (IOException var5) {

        throw new InternalError("unexpected I/O Exception");

      }

    }

  } 

private void addProxyMethod(Method var1, Class var2) {

    String var3 = var1.getName(); //方法名

    Class[] var4 = var1.getParameterTypes();  //方法参数类型数组

    Class var5 = var1.getReturnType();  //返回值类型 

    Class[] var6 = var1.getExceptionTypes();  //异常类型

    String var7 = var3 + getParameterDescriptors(var4);  //方法签名

    Object var8 = (List)this.proxyMethods.get(var7);  //根据方法签名却获得proxyMethods的Value

    if(var8 != null) {  //处理多个代理接口中重复的方法的情况

      Iterator var9 = ((List)var8).iterator();

      while(var9.hasNext()) {

        ProxyGenerator.ProxyMethod var10 = (ProxyGenerator.ProxyMethod)var9.next();

        if(var5 == var10.returnType) {

          /*归约异常类型以至于让重写的方法抛出合适的异常类型，我认为这里可能是多个接口中有相同的方法，而这些相同的方法抛出的异常类           型又不同，所以对这些相同方法抛出的异常进行了归约*/

          ArrayList var11 = new ArrayList();

          collectCompatibleTypes(var6, var10.exceptionTypes, var11);

          collectCompatibleTypes(var10.exceptionTypes, var6, var11);

          var10.exceptionTypes = new Class[var11.size()];

          //将ArrayList转换为Class对象数组

          var10.exceptionTypes = (Class[])var11.toArray(var10.exceptionTypes);

          return;

        }

      }

    } else {

      var8 = new ArrayList(3);

      this.proxyMethods.put(var7, var8);

    }   

    ((List)var8).add(new ProxyGenerator.ProxyMethod(var3, var4, var5, var6, var2, null));

    /*24~27行的意思就是如果var8为空，就创建一个数组，并以方法签名为key,proxymethod对象数组为value添加到proxyMethods*/

  } 

public final class $Proxy0 extends Proxy implements IHello {  //继承了Proxy类和实现IHello接口

  //变量，都是private static Method XXX

  private static Method m3;  

  private static Method m1;

  private static Method m0;

  private static Method m2;

  //代理类的构造函数，其参数正是是InvocationHandler实例，Proxy.newInstance方法就是通过通过这个构造函数来创建代理实例的

  public $Proxy0(InvocationHandler var1) throws {

    super(var1);

  }

  //接口代理方法

  public final void sayHello() throws {

    try {

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

    } catch (RuntimeException | Error var2) {

      throw var2;

    } catch (Throwable var3) {

      throw new UndeclaredThrowableException(var3);

    }

  }

  //以下Object中的三个方法

  public final boolean equals(Object var1) throws {

    try {

      return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();

    } catch (RuntimeException | Error var3) {

      throw var3;

    } catch (Throwable var4) {

      throw new UndeclaredThrowableException(var4);

    }

  }

  public final int hashCode() throws {

    try {

      return ((Integer)super.h.invoke(this, m0, (Object[])null)).intValue();

    } catch (RuntimeException | Error var2) {

      throw var2;

    } catch (Throwable var3) {

      throw new UndeclaredThrowableException(var3);

    }

  }

  public final String toString() throws {

    try {

      return (String)super.h.invoke(this, m2, (Object[])null);

    } catch (RuntimeException | Error var2) {

      throw var2;

    } catch (Throwable var3) {

      throw new UndeclaredThrowableException(var3);

    }

  }

  //对变量进行一些初始化工作

  static {

    try { 

      m3 = Class.forName("com.mobin.proxy.IHello").getMethod("sayHello", new Class[0]);

      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});

      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);

      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);

    } catch (NoSuchMethodException var2) {

      throw new NoSuchMethodError(var2.getMessage());

    } catch (ClassNotFoundException var3) {

      throw new NoClassDefFoundError(var3.getMessage());

    }

  }

}