Java JDK动态代理（AOP）的实现原理与使用详析

publicobject invoke(Object obj,Method method, Object[] args) 

package jiankunking; 
 
/** 
 * 需要动态代理的接口 
 */ 
public interface Subject 
{ 
 /** 
 * 你好 
 * 
 * @param name 
 * @return 
 */ 
 public String SayHello(String name); 
 
 /** 
 * 再见 
 * 
 * @return 
 */ 
 public String SayGoodBye(); 
} 

package jiankunking; 
 
/** 
 * 实际对象 
 */ 
public class RealSubject implements Subject 
{ 
 
 /** 
 * 你好 
 * 
 * @param name 
 * @return 
 */ 
 public String SayHello(String name) 
 { 
 return "hello " + name; 
 } 
 
 /** 
 * 再见 
 * 
 * @return 
 */ 
 public String SayGoodBye() 
 { 
 return " good bye "; 
 } 
} 

package jiankunking; 
 
import java.lang.reflect.InvocationHandler; 
import java.lang.reflect.Method; 
 
 
/** 
 * 调用处理器实现类 
 * 每次生成动态代理类对象时都需要指定一个实现了该接口的调用处理器对象 
 */ 
public class InvocationHandlerImpl implements InvocationHandler 
{ 
 
 /** 
 * 这个就是我们要代理的真实对象 
 */ 
 private Object subject; 
 
 /** 
 * 构造方法，给我们要代理的真实对象赋初值 
 * 
 * @param subject 
 */ 
 public InvocationHandlerImpl(Object subject) 
 { 
 this.subject = subject; 
 } 
 
 /** 
 * 该方法负责集中处理动态代理类上的所有方法调用。 
 * 调用处理器根据这三个参数进行预处理或分派到委托类实例上反射执行 
 * 
 * @param proxy 代理类实例 
 * @param method 被调用的方法对象 
 * @param args 调用参数 
 * @return 
 * @throws Throwable 
 */ 
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable 
 { 
 //在代理真实对象前我们可以添加一些自己的操作 
 System.out.println("在调用之前，我要干点啥呢？"); 
 
 System.out.println("Method:" + method); 
 
 //当代理对象调用真实对象的方法时，其会自动的跳转到代理对象关联的handler对象的invoke方法来进行调用 
 Object returnValue = method.invoke(subject, args); 
 
 //在代理真实对象后我们也可以添加一些自己的操作 
 System.out.println("在调用之后，我要干点啥呢？"); 
 
 return returnValue; 
 } 
} 

package jiankunking; 
 
import java.lang.reflect.InvocationHandler; 
import java.lang.reflect.Proxy; 
 
/** 
 * 动态代理演示 
 */ 
public class DynamicProxyDemonstration 
{ 
 public static void main(String[] args) 
 { 
 //代理的真实对象 
 Subject realSubject = new RealSubject(); 
 
 /** 
 * InvocationHandlerImpl 实现了 InvocationHandler 接口，并能实现方法调用从代理类到委托类的分派转发 
 * 其内部通常包含指向委托类实例的引用，用于真正执行分派转发过来的方法调用. 
 * 即：要代理哪个真实对象，就将该对象传进去，最后是通过该真实对象来调用其方法 
 */ 
 InvocationHandler handler = new InvocationHandlerImpl(realSubject); 
 
 ClassLoader loader = realSubject.getClass().getClassLoader(); 
 Class[] interfaces = realSubject.getClass().getInterfaces(); 
 /** 
 * 该方法用于为指定类装载器、一组接口及调用处理器生成动态代理类实例 
 */ 
 Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler); 
 
 System.out.println("动态代理对象的类型："+subject.getClass().getName()); 
 
 String hello = subject.SayHello("jiankunking"); 
 System.out.println(hello); 
// String goodbye = subject.SayGoodBye(); 
// System.out.println(goodbye); 
 } 
 
} 

Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler); 

/** 
 * Returns an instance of a proxy class for the specified interfaces 
 * that dispatches method invocations to the specified invocation 
 * handler. 
 * 
 * <p>{@code Proxy.newProxyInstance} throws 
 * {@code IllegalArgumentException} for the same reasons that 
 * {@code Proxy.getProxyClass} does. 
 * 
 * @param loader the class loader to define the proxy class 
 * @param interfaces the list of interfaces for the proxy class 
 * to implement 
 * @param h the invocation handler to dispatch method invocations to 
 * @return a proxy instance with the specified invocation handler of a 
 * proxy class that is defined by the specified class loader 
 * and that implements the specified interfaces 
 * @throws IllegalArgumentException if any of the restrictions on the 
 * parameters that may be passed to {@code getProxyClass} 
 * are violated 
 * @throws SecurityException if a security manager, <em>s</em>, is present 
 * and any of the following conditions is met: 
 * <ul> 
 * <li> the given {@code loader} is {@code null} and 
 * the caller's class loader is not {@code null} and the 
 * invocation of {@link SecurityManager#checkPermission 
 * s.checkPermission} with 
 * {@code RuntimePermission("getClassLoader")} permission 
 * denies access;</li> 
 * <li> for each proxy interface, {@code intf}, 
 * the caller's class loader is not the same as or an 
 * ancestor of the class loader for {@code intf} and 
 * invocation of {@link SecurityManager#checkPackageAccess 
 * s.checkPackageAccess()} denies access to {@code intf};</li> 
 * <li> any of the given proxy interfaces is non-public and the 
 * caller class is not in the same {@linkplain Package runtime package} 
 * as the non-public interface and the invocation of 
 * {@link SecurityManager#checkPermission s.checkPermission} with 
 * {@code ReflectPermission("newProxyInPackage.{package name}")} 
 * permission denies access.</li> 
 * </ul> 
 * @throws NullPointerException if the {@code interfaces} array 
 * argument or any of its elements are {@code null}, or 
 * if the invocation handler, {@code h}, is 
 * {@code null} 
 */ 
@CallerSensitive 
public static Object newProxyInstance(ClassLoader loader, 
   Class<?>[] interfaces, 
   InvocationHandler h) 
 throws IllegalArgumentException 
 { 
 //检查h 不为空，否则抛异常 
 Objects.requireNonNull(h); 
 
 final Class<?>[] intfs = interfaces.clone(); 
 final SecurityManager sm = System.getSecurityManager(); 
 if (sm != null) { 
 checkProxyAccess(Reflection.getCallerClass(), loader, intfs); 
 } 
 
 /* 
 * 获得与指定类装载器和一组接口相关的代理类类型对象 
 */ 
 Class<?> cl = getProxyClass0(loader, intfs); 
 
 /* 
 * 通过反射获取构造函数对象并生成代理类实例 
 */ 
 try { 
 if (sm != null) { 
 checkNewProxyPermission(Reflection.getCallerClass(), cl); 
 } 
 //获取代理对象的构造方法（也就是$Proxy0(InvocationHandler h)） 
 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; 
  } 
 }); 
 } 
 //生成代理类的实例并把InvocationHandlerImpl的实例传给它的构造方法 
 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); 
 } 
 } 

/** 
 * Generate a proxy class. Must call the checkProxyAccess method 
 * to perform permission checks before calling this. 
 */ 
 private static Class<?> getProxyClass0(ClassLoader loader, 
   Class<?>... interfaces) { 
 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 
 return proxyClassCache.get(loader, interfaces); 
 } 

/** 
 * a cache of proxy classes 
 */ 
 private static final WeakCache<ClassLoader, Class<?>[], Class<?>> 
 proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); 

/** 
 * Look-up the value through the cache. This always evaluates the 
 * {@code subKeyFactory} function and optionally evaluates 
 * {@code valueFactory} function if there is no entry in the cache for given 
 * pair of (key, subKey) or the entry has already been cleared. 
 * 
 * @param key possibly null key 
 * @param parameter parameter used together with key to create sub-key and 
 *  value (should not be null) 
 * @return the cached value (never null) 
 * @throws NullPointerException if {@code parameter} passed in or 
 *  {@code sub-key} calculated by 
 *  {@code subKeyFactory} or {@code value} 
 *  calculated by {@code valueFactory} is null. 
 */ 
 public V get(K key, P parameter) { 
 Objects.requireNonNull(parameter); 
 
 expungeStaleEntries(); 
 
 Object cacheKey = CacheKey.valueOf(key, refQueue); 
 
 // lazily install the 2nd level valuesMap for the particular cacheKey 
 ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey); 
 if (valuesMap == null) { 
 //putIfAbsent这个方法在key不存在的时候加入一个值,如果key存在就不放入 
 ConcurrentMap<Object, Supplier<V>> oldValuesMap 
 = map.putIfAbsent(cacheKey, 
   valuesMap = new ConcurrentHashMap<>()); 
 if (oldValuesMap != null) { 
 valuesMap = oldValuesMap; 
 } 
 } 
 
 // create subKey and retrieve the possible Supplier<V> stored by that 
 // subKey from valuesMap 
 Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter)); 
 Supplier<V> supplier = valuesMap.get(subKey); 
 Factory factory = null; 
 
 while (true) { 
 if (supplier != null) { 
 // supplier might be a Factory or a CacheValue<V> instance 
 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 synchronized V get() { // serialize access 
 // re-check 
 Supplier<V> supplier = valuesMap.get(subKey); 
 if (supplier != this) { 
 // something changed while we were waiting: 
 // might be that we were replaced by a CacheValue 
 // or were removed because of failure -> 
 // return null to signal WeakCache.get() to retry 
 // the loop 
 return null; 
 } 
 // else still us (supplier == this) 
 
 // create new value 
 V value = null; 
 try { 
 value = Objects.requireNonNull(valueFactory.apply(key, parameter)); 
 } finally { 
 if (value == null) { // remove us on failure 
  valuesMap.remove(subKey, this); 
 } 
 } 
 // the only path to reach here is with non-null value 
 assert value != null; 
 
 // wrap value with CacheValue (WeakReference) 
 CacheValue<V> cacheValue = new CacheValue<>(value); 
 
 // try replacing us with CacheValue (this should always succeed) 
 if (valuesMap.replace(subKey, this, cacheValue)) { 
 // put also in reverseMap 
 reverseMap.put(cacheValue, Boolean.TRUE); 
 } else { 
 throw new AssertionError("Should not reach here"); 
 } 
 
 // successfully replaced us with new CacheValue -> return the value 
 // wrapped by it 
 return value; 
 } 
 } 

/** 
 * 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 
 private static final String proxyClassNamePrefix = "$Proxy"; 
 
 // next number to use for generation of unique proxy class names 
 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. 
 */ 
 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. 
 */ 
 if (!interfaceClass.isInterface()) { 
  throw new IllegalArgumentException( 
  interfaceClass.getName() + " is not an interface"); 
 } 
 /* 
 * Verify that this interface is not a duplicate. 
 */ 
 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. 
 */ 
 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. 
 */ 
 long num = nextUniqueNumber.getAndIncrement(); 
 String proxyName = proxyPkg + proxyClassNamePrefix + num; 
 
 /* 
 * Generate the specified proxy class. 
 */ 
 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()); 
 } 
 } 
 } 

//生成字节码 
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(proxyName, interfaces, accessFlags); 

package jiankunking; 
 
import sun.misc.ProxyGenerator; 
 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.lang.reflect.InvocationHandler; 
import java.lang.reflect.Proxy; 
 
/** 
 * 动态代理演示 
 */ 
public class DynamicProxyDemonstration 
{ 
 public static void main(String[] args) 
 { 
 //代理的真实对象 
 Subject realSubject = new RealSubject(); 
 
 /** 
 * InvocationHandlerImpl 实现了 InvocationHandler 接口，并能实现方法调用从代理类到委托类的分派转发 
 * 其内部通常包含指向委托类实例的引用，用于真正执行分派转发过来的方法调用. 
 * 即：要代理哪个真实对象，就将该对象传进去，最后是通过该真实对象来调用其方法 
 */ 
 InvocationHandler handler = new InvocationHandlerImpl(realSubject); 
 
 ClassLoader loader = handler.getClass().getClassLoader(); 
 Class[] interfaces = realSubject.getClass().getInterfaces(); 
 /** 
 * 该方法用于为指定类装载器、一组接口及调用处理器生成动态代理类实例 
 */ 
 Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler); 
 
 System.out.println("动态代理对象的类型："+subject.getClass().getName()); 
 
 String hello = subject.SayHello("jiankunking"); 
 System.out.println(hello); 
 // 将生成的字节码保存到本地， 
 createProxyClassFile(); 
 } 
 private static void createProxyClassFile(){ 
 String name = "ProxySubject"; 
 byte[] data = ProxyGenerator.generateProxyClass(name,new Class[]{Subject.class}); 
 FileOutputStream out =null; 
 try { 
 out = new FileOutputStream(name+".class"); 
 System.out.println((new File("hello")).getAbsolutePath()); 
 out.write(data); 
 } catch (FileNotFoundException e) { 
 e.printStackTrace(); 
 } catch (IOException e) { 
 e.printStackTrace(); 
 }finally { 
 if(null!=out) try { 
 out.close(); 
 } catch (IOException e) { 
 e.printStackTrace(); 
 } 
 } 
 } 
 
} 

import java.lang.reflect.InvocationHandler; 
import java.lang.reflect.Method; 
import java.lang.reflect.Proxy; 
import java.lang.reflect.UndeclaredThrowableException; 
import jiankunking.Subject; 
 
public final class ProxySubject 
 extends Proxy 
 implements Subject 
{ 
 private static Method m1; 
 private static Method m3; 
 private static Method m4; 
 private static Method m2; 
 private static Method m0; 
 
 public ProxySubject(InvocationHandler paramInvocationHandler) 
 { 
 super(paramInvocationHandler); 
 } 
 
 public final boolean equals(Object paramObject) 
 { 
 try 
 { 
 return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue(); 
 } 
 catch (Error|RuntimeException localError) 
 { 
 throw localError; 
 } 
 catch (Throwable localThrowable) 
 { 
 throw new UndeclaredThrowableException(localThrowable); 
 } 
 } 
 
 public final String SayGoodBye() 
 { 
 try 
 { 
 return (String)this.h.invoke(this, m3, null); 
 } 
 catch (Error|RuntimeException localError) 
 { 
 throw localError; 
 } 
 catch (Throwable localThrowable) 
 { 
 throw new UndeclaredThrowableException(localThrowable); 
 } 
 } 
 
 public final String SayHello(String paramString) 
 { 
 try 
 { 
 return (String)this.h.invoke(this, m4, new Object[] { paramString }); 
 } 
 catch (Error|RuntimeException localError) 
 { 
 throw localError; 
 } 
 catch (Throwable localThrowable) 
 { 
 throw new UndeclaredThrowableException(localThrowable); 
 } 
 } 
 
 public final String toString() 
 { 
 try 
 { 
 return (String)this.h.invoke(this, m2, null); 
 } 
 catch (Error|RuntimeException localError) 
 { 
 throw localError; 
 } 
 catch (Throwable localThrowable) 
 { 
 throw new UndeclaredThrowableException(localThrowable); 
 } 
 } 
 
 public final int hashCode() 
 { 
 try 
 { 
 return ((Integer)this.h.invoke(this, m0, null)).intValue(); 
 } 
 catch (Error|RuntimeException localError) 
 { 
 throw localError; 
 } 
 catch (Throwable localThrowable) 
 { 
 throw new UndeclaredThrowableException(localThrowable); 
 } 
 } 
 
 static 
 { 
 try 
 { 
 m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") }); 
 m3 = Class.forName("jiankunking.Subject").getMethod("SayGoodBye", new Class[0]); 
 m4 = Class.forName("jiankunking.Subject").getMethod("SayHello", new Class[] { Class.forName("java.lang.String") }); 
 m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]); 
 m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]); 
 return; 
 } 
 catch (NoSuchMethodException localNoSuchMethodException) 
 { 
 throw new NoSuchMethodError(localNoSuchMethodException.getMessage()); 
 } 
 catch (ClassNotFoundException localClassNotFoundException) 
 { 
 throw new NoClassDefFoundError(localClassNotFoundException.getMessage()); 
 } 
 } 
} 

Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler); 

public final String SayHello(String paramString)