深入浅析java 1.8 中动态代理的原理

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()); } } }

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