java 1.8 动态代理源码深度分析

class proxyed implements pro{ @Override public void text() {  System.err.println("本方法"); }}interface pro { void text();}public class JavaProxy implements InvocationHandler {  private Object source;  public JavaProxy(Object source) {   super();   this.source = source;  }  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {   System.out.println("before");   Object invoke = method.invoke(source, args);   System.out.println("after");   return invoke;  }  public Object getProxy(){   return Proxy.newProxyInstance(getClass().getClassLoader(), source.getClass().getInterfaces(), this);  }  public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchMethodException {   //第一种，自己写   //1.设置saveGeneratedFiles值为true则生成 class字节码文件方便分析   System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");   //2.获取动态代理类   Class proxyClazz = Proxy.getProxyClass(pro.class.getClassLoader(),pro.class);   //3.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);   //4.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   pro iHello = (pro) constructor.newInstance(new JavaProxy(new proxyed()));   //5.通过代理对象调用目标方法   iHello.text();   //第二种，调用JDK提供的方法，实现了2~4步   Proxy.newProxyInstance(JavaProxy.class.getClassLoader(),proxyed.class.getInterfaces(),new JavaProxy(new proxyed()));  }}

public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException {  //Objects.requireNonNull 判空方法，之后所有的单纯的判断null并抛异常，都是此方法  Objects.requireNonNull(h);  //clone 类实现的所有接口  final Class<?>[] intfs = interfaces.clone();  //获取当前系统安全接口  final SecurityManager sm = System.getSecurityManager();  if (sm != null) {   //Reflection.getCallerClass返回调用该方法的方法的调用类;loader：接口的类加载器   //进行包访问权限、类加载器权限等检查   checkProxyAccess(Reflection.getCallerClass(), loader, intfs);  }  /*   * Look up or generate the designated proxy class.   * 查找或生成代理类   */  Class<?> cl = getProxyClass0(loader, intfs);  /*   * Invoke its constructor with the designated invocation handler.   * 使用指定的调用处理程序调用它的构造函数   */  try {   if (sm != null) {    checkNewProxyPermission(Reflection.getCallerClass(), cl);   }   //获取构造   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;     }    });   }   //返回 代理对象   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);  } }

/**  * a cache of proxy classes：动态代理类的弱缓存容器  * KeyFactory:根据接口的数量，映射一个最佳的key生成函数,其中表示接口的类对象被弱引用；也就是key对象被弱引用继承自WeakReference（key0、key1、key2、keyX），保存接口密钥(hash值)  * ProxyClassFactory：生成动态类的工厂  * 注意，两个都实现了BiFunction<ClassLoader, Class<?>[], Object>接口  */ private static final WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); /**  * Generate a proxy class. Must call the checkProxyAccess method  * to perform permission checks before calling this.  * 生成代理类，调用前必须进行 checkProxyAccess权限检查，所以newProxyInstance进行了权限检查  */ private static Class<?> getProxyClass0(ClassLoader loader, Class<?>... interfaces) {  //实现接口的最大数量<65535;谁写的类能实现这么多接口  if (interfaces.length > 65535) {   throw new IllegalArgumentException("interface limit exceeded");  }  // If the proxy class defined by the given loader implementing  // the given interfaces exists, this will simply return the cached copy;  // otherwise, it will create the proxy class via the ProxyClassFactory  // 如果缓存中有，就直接返回，否则会生成  return proxyClassCache.get(loader, interfaces); }

public V get(K key, P parameter) {  //key：类加载器；parameter：接口数组  Objects.requireNonNull(parameter);  //清除已经被GC回收的弱引用  expungeStaleEntries();  //CacheKey弱引用类，refQueue已经被回收的弱引用队列；构建一个CacheKey  Object cacheKey = CacheKey.valueOf(key, refQueue);    //map一级缓存，获取valuesMap二级缓存  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;   }  }  // subKeyFactory类型是KeyFactory，apply返回表示接口的key  Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));  //Factory 实现了supplier，我们实际是获取缓存中的Factory，调用其get方法  Supplier<V> supplier = valuesMap.get(subKey);  Factory factory = null;    //下面用到了 CAS+重试 实现的多线程安全的 非阻塞算法  while (true) {   if (supplier != null) {    // 只需要知道，最终会调用get方法，此supplier可能是缓存中取出来的，也可能是Factory新new出来的    V value = supplier.get();    if (value != null) {     return value;    }   }   // else no supplier in cache   // or a supplier that returned null (could be a cleared CacheValue   // or a Factory that wasn't successful in installing the CacheValue)   // lazily construct a Factory   if (factory == null) {    factory = new Factory(key, parameter, subKey, valuesMap);   }   if (supplier == null) {    supplier = valuesMap.putIfAbsent(subKey, factory);    if (supplier == null) {     // successfully installed Factory     supplier = factory;    }    // else retry with winning supplier   } else {    if (valuesMap.replace(subKey, supplier, factory)) {     // successfully replaced     // cleared CacheEntry / unsuccessful Factory     // with our Factory     supplier = factory;    } else {     // retry with current supplier     supplier = valuesMap.get(subKey);    }   }  } }

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.     * 类加载器和接口名解析出的是同一个     */   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");   }    /*     * Verify that the Class object actually represents an interface.     * 确保是一个接口     */   if (!interfaceClass.isInterface()) {    throw new IllegalArgumentException( interfaceClass.getName() + " is not an interface");   }    /*     * Verify that this interface is not a duplicate.     * 确保接口没重复     */   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.    * 验证所有非公共的接口在同一个包内；公共的就无需处理    */  for (Class<?> intf : interfaces) {   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.    * proxyClassNamePrefix = $Proxy    * nextUniqueNumber 是一个原子类，确保多线程安全，防止类名重复，类似于：$Proxy0，$Proxy1......    */  long num = nextUniqueNumber.getAndIncrement();  String proxyName = proxyPkg + proxyClassNamePrefix + num;   /*    * Generate the specified proxy class.    * 生成类字节码的方法:重点    */  byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces, accessFlags);  try {   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 byte[] generateProxyClass(final String name, Class<?>[] interfaces, int accessFlags) {  ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);  //真正生成字节码的方法  final byte[] classFile = gen.generateClassFile();  //如果saveGeneratedFiles为true 则生成字节码文件，所以在开始我们要设置这个参数  //当然，也可以通过返回的bytes自己输出  if (saveGeneratedFiles) {   java.security.AccessController.doPrivileged( new java.security.PrivilegedAction<Void>() {      public Void run() {       try {        int i = name.lastIndexOf('.');        Path path;        if (i > 0) {         Path dir = Paths.get(name.substring(0, i).replace('.', File.separatorChar));         Files.createDirectories(dir);         path = dir.resolve(name.substring(i+1, name.length()) + ".class");        } else {         path = Paths.get(name + ".class");        }        Files.write(path, classFile);        return null;       } catch (IOException e) {        throw new InternalError( "I/O exception saving generated file: " + e);       }      }     });  }  return classFile; }

private byte[] generateClassFile() {  /* ============================================================   * Step 1: Assemble ProxyMethod objects for all methods to generate proxy dispatching code for.   * 步骤1：为所有方法生成代理调度代码，将代理方法对象集合起来。   */  //增加 hashcode、equals、toString方法  addProxyMethod(hashCodeMethod, Object.class);  addProxyMethod(equalsMethod, Object.class);  addProxyMethod(toStringMethod, Object.class);  //增加接口方法  for (Class<?> intf : interfaces) {   for (Method m : intf.getMethods()) {    addProxyMethod(m, intf);   }  }  /*   * 验证方法签名相同的一组方法，返回值类型是否相同；意思就是重写方法要方法签名和返回值一样   */  for (List<ProxyMethod> sigmethods : proxyMethods.values()) {   checkReturnTypes(sigmethods);  }  /* ============================================================   * Step 2: Assemble FieldInfo and MethodInfo structs for all of fields and methods in the class we are generating.   * 为类中的方法生成字段信息和方法信息   */  try {   //增加构造方法   methods.add(generateConstructor());   for (List<ProxyMethod> sigmethods : proxyMethods.values()) {    for (ProxyMethod pm : sigmethods) {     // add static field for method's Method object     fields.add(new FieldInfo(pm.methodFieldName,       "Ljava/lang/reflect/Method;",       ACC_PRIVATE | ACC_STATIC));     // generate code for proxy method and add it     methods.add(pm.generateMethod());    }   }   //增加静态初始化信息   methods.add(generateStaticInitializer());  } catch (IOException e) {   throw new InternalError("unexpected I/O Exception", e);  }  if (methods.size() > 65535) {   throw new IllegalArgumentException("method limit exceeded");  }  if (fields.size() > 65535) {   throw new IllegalArgumentException("field limit exceeded");  }  /* ============================================================   * Step 3: Write the final class file.   * 步骤3：编写最终类文件   */  /*   * Make sure that constant pool indexes are reserved for the following items before starting to write the final class file.   * 在开始编写最终类文件之前，确保为下面的项目保留常量池索引。   */  cp.getClass(dotToSlash(className));  cp.getClass(superclassName);  for (Class<?> intf: interfaces) {   cp.getClass(dotToSlash(intf.getName()));  }  /*   * Disallow new constant pool additions beyond this point, since we are about to write the final constant pool table.   * 设置只读，在这之前不允许在常量池中增加信息，因为要写常量池表   */  cp.setReadOnly();  ByteArrayOutputStream bout = new ByteArrayOutputStream();  DataOutputStream dout = new DataOutputStream(bout);  try {   // u4 magic;   dout.writeInt(0xCAFEBABE);   // u2 次要版本;   dout.writeShort(CLASSFILE_MINOR_VERSION);   // u2 主版本   dout.writeShort(CLASSFILE_MAJOR_VERSION);   cp.write(dout);    // (write constant pool)   // u2 访问标识;   dout.writeShort(accessFlags);   // u2 本类名;   dout.writeShort(cp.getClass(dotToSlash(className)));   // u2 父类名;   dout.writeShort(cp.getClass(superclassName));   // u2 接口;   dout.writeShort(interfaces.length);   // u2 interfaces[interfaces_count];   for (Class<?> intf : interfaces) {    dout.writeShort(cp.getClass(      dotToSlash(intf.getName())));   }   // u2 字段;   dout.writeShort(fields.size());   // field_info fields[fields_count];   for (FieldInfo f : fields) {    f.write(dout);   }   // u2 方法;   dout.writeShort(methods.size());   // method_info methods[methods_count];   for (MethodInfo m : methods) {    m.write(dout);   }   // u2 类文件属性：对于代理类来说没有类文件属性;   dout.writeShort(0); // (no ClassFile attributes for proxy classes)  } catch (IOException e) {   throw new InternalError("unexpected I/O Exception", e);  }  return bout.toByteArray(); }

final class $Proxy0 extends Proxy implements pro {  //fields   private static Method m1;  private static Method m2;  private static Method m3;  private static Method m0;  public $Proxy0(InvocationHandler var1) throws {   super(var1);  }  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 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);   }  }  public final void text() throws {   try {    //实际就是调用代理类的invoke方法     super.h.invoke(this, m3, (Object[])null);   } catch (RuntimeException | Error var2) {    throw var2;   } catch (Throwable var3) {    throw new UndeclaredThrowableException(var3);   }  }  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);   }  }  static {   try {    //这里每个方法对象 和类的实际方法绑定    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]);    m3 = Class.forName("spring.commons.api.study.CreateModel.pro").getMethod("text", 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());   }  } }