JDK动态代理原理

public class ProxySubject implements InvocationHandler {    private Object target;    /**     * @param obj     *            真实对象     * @return 代理对象     */    public Object bind(Object obj) {        this.target = obj;        return Proxy.newProxyInstance(obj.getClass().getClassLoader(), obj.getClass().getInterfaces(), this);    }    /*     *  返回调用实例方法的返回值     */    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        return method.invoke(target);    }}

动态代理实现原理

//动态代理类的参数类型private static final Class<?>[] constructorParams ={ InvocationHandler.class };protected InvocationHandler h;//构造方法私有化，不允许外部实例化对象，单例设计private Proxy() {    }//有参的也被被封装起来，用protecct貌似是为了方便吧子类调用protected Proxy(InvocationHandler h) {        Objects.requireNonNull(h);        this.h = h;    } //提供统一的获取代理类的实例方法（摘要主要的方法，其他省略）   public static Object newProxyInstance(ClassLoader loader,  Class<?>[] interfaces,InvocationHandler h)throws IllegalArgumentException {//类似有getClass,Class.forName()的一个获取Class对象的方法Class<?> cl = getProxyClass0(loader, intfs);//反射获得构造final Constructor<?> cons = cl.getConstructor(constructorParams); final InvocationHandler ih = h;//代理类返回实例化对象return cons.newInstance(new Object[]{h});}

 private static Class<?> getProxyClass0(ClassLoader loader,                                           Class<?>... interfaces) {        if (interfaces.length > 65535) {            throw new IllegalArgumentException("interface limit exceeded");        }        //它将通过proxyclassfactory创建代理类        // 给定的接口存在，从缓存中获取        return proxyClassCache.get(loader, interfaces);    }

private static final WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

KeyFactory获得类加载器和接口

ProxyClassFactory 获得真正的代理类

 //这是代理类工厂类      private static final class ProxyClassFactory          implements BiFunction<ClassLoader, Class<?>[], Class<?>>      {          //定义的名字前缀          private static final String proxyClassNamePrefix = "$Proxy";          // 生成的数,跟在$Proxy这个名字之后,JDK动态代理类的名字都是 $ProxyN (N=0,1,2,3,4,5,6,7,8)         private static final AtomicLong nextUniqueNumber = new AtomicLong();           //验证类加载器是否解析过这个接口        @Override          public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {              Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);              for (Class<?> intf : interfaces) {                  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");                  }                  //判断Class对象是否代表的是一个接口                  if (!interfaceClass.isInterface()) {                      throw new IllegalArgumentException(                          interfaceClass.getName() + " is not an interface");                  }                  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;              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 + ".";              }              long num = nextUniqueNumber.getAndIncrement();              String proxyName = proxyPkg + proxyClassNamePrefix + num;              //产生本地字节文件              byte[] proxyClassFile = ProxyGenerator.generateProxyClass(                  proxyName, interfaces, accessFlags);              try {                  //按照产生的字节码文件来产生动态代理类                  return defineClass0(loader, proxyName,                                      proxyClassFile, 0, proxyClassFile.length);              } catch (ClassFormatError e) {                  throw new IllegalArgumentException(e.toString());              }          }      }  

 public static byte[] generateProxyClass(final String name,                                                 Class[] interfaces)         {             ProxyGenerator gen = new ProxyGenerator(name, interfaces);          // 这里动态生成代理类的字节码，比较复杂           final byte[] classFile = gen.generateClassFile();          // 把所生成的代理类的字节码保存到硬盘上             if (saveGeneratedFiles) {                 java.security.AccessController.doPrivileged(                 new java.security.PrivilegedAction<Void>() {                     public Void run() {                         try {                             FileOutputStream file =                                 new FileOutputStream(dotToSlash(name) + ".class");                             file.write(classFile);                             file.close();                             return null;                         } catch (IOException e) {                             throw new InternalError(                                 "I/O exception saving generated file: " + e);                         }                     }                 });             }          // 返回代理类的字节码             return classFile;         }  

JNI调用原生态方法

 private static native Class<?> defineClass0(ClassLoader loader, String name,byte[] b, int off, int len);