java 1.8 动态代理源码深度分析

JDK8动态代理源码分析

动态代理的基本使用就不详细介绍了：

例子：

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()));
  }
}

入口：newProxyInstance

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);
  }

  
  Class cl = getProxyClass0(loader, intfs);

  
  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() {
     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);
  }
 }

从上面的分析中可以看出，newProxyInstance帮我们执行了生成代理类----获取构造器----生成代理对象这三步；

我们重点分析生成代理类

getProxyClass0

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

 
 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);
 }

proxyClassCache.get

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> valuesMap = map.get(cacheKey);
  if (valuesMap == null) {
   ConcurrentMap> 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 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);
    }
   }
  }
 }

supplier.get

这个方法中会调用ProxyClassFactory的apply方法，就不过多介绍

ProxyClassFactory.apply

public Class apply(ClassLoader loader, Class[] interfaces) {

  Map, 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");
   }
    
   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;
   
  byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces, accessFlags);
  try {
   return defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length);
  } catch (ClassFormatError e) {
    
   throw new IllegalArgumentException(e.toString());
  }
 }

ProxyGenerator.generateProxyClass

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() {
      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;
 }

最终方法

private byte[] generateClassFile() {
  
  //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);
   }
  }

  
  for (List sigmethods : proxyMethods.values()) {
   checkReturnTypes(sigmethods);
  }

  
  try {
   //增加构造方法
   methods.add(generateConstructor());
   for (List 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");
  }

  
  
  cp.getClass(dotToSlash(className));
  cp.getClass(superclassName);
  for (Class intf: interfaces) {
   cp.getClass(dotToSlash(intf.getName()));
  }

  
  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();
 }

生成的字节码反编译

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());
   }
  }
 }

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