CGLIB动态代理示例与源码解析

1. 原理，代理模式

代理模式的本质：调用方--->代理方--->实现方。

不细介绍，看我上一篇文章 JDK8动态代理示例与原码解析

1.1 动态代理模式步骤

      生成代理类二进制字节码，可配置参数生成文件。

      classloader load二进制字节码，生成Class对象( 可使用public static Class forName(String className))

      Class对象反射构造方法，构造方法newInstance创建对象

2. CGLib代理示例

pom.xml加入

    cglib
    cglib
    3.2.5

public class HelloService {
    public void sayHello(String something) {
        System.out.println("hello, " + something);
    }
}

public class HelloCGLibProxy implements MethodInterceptor {

    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("-----------"+method.getName()+"-------");
        return methodProxy.invokeSuper(o, objects);
    }
}

public static void main(String[] args) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(HelloService.class);
        enhancer.setCallback(new HelloCGLibProxy());

        Object obj = enhancer.create();
        HelloService helloService = (HelloService) obj;
        helloService.sayHello("ok");
}


-----------sayHello-------
hello, ok

3. 源码分析

核心方法

enhancer.create()

 看注释一目了然，Generate a new class if necessary

    /**
     * Generate a new class if necessary and uses the specified
     * callbacks (if any) to create a new object instance.
     * Uses the no-arg constructor of the superclass.
     * @return a new instance
     */
    public Object create() {
        classOnly = false;
        argumentTypes = null;
        return createHelper();
    }

createHelper()

    private static final EnhancerKey KEY_FACTORY =
      (EnhancerKey)KeyFactory.create(EnhancerKey.class, KeyFactory.HASH_ASM_TYPE, null);

    public interface EnhancerKey {
        public Object newInstance(String type,
                                  String[] interfaces,
                                  WeakCacheKey filter,
                                  Type[] callbackTypes,
                                  boolean useFactory,
                                  boolean interceptDuringConstruction,
                                  Long serialVersionUID);
    }

    private Object createHelper() {
        //验证
        preValidate();
        //生成key，EnhancerKey KEY_FACTORY初始化的时候，通过CGLIB动态生成实现类
        //先自己CGLIB给自己动态创建实现类了
        Object key = KEY_FACTORY.newInstance((superclass != null) ? superclass.getName() : null,
                ReflectUtils.getNames(interfaces),
                filter == ALL_ZERO ? null : new WeakCacheKey(filter),
                callbackTypes,
                useFactory,
                interceptDuringConstruction,
                serialVersionUID);
        this.currentKey = key;
        //父类使用EnhancerKey创建对象
        Object result = super.create(key);
        return result;
    }

调试看图，传入了代理的类对象和方法拦截器（CGLIB的核心思想）

3.1 创建KeyFactory对象，此处居然就使用了CGLIB动态代理技术，下面逐一分析。

KeyFactory.create(EnhancerKey.class, KeyFactory.HASH_ASM_TYPE, null)
//动态创建EnhancerKey实现类

    public static KeyFactory create(ClassLoader loader, Class keyInterface, KeyFactoryCustomizer customizer,
                                    List next) {
        Generator gen = new Generator();
        gen.setInterface(keyInterface);

        if (customizer != null) {
            gen.addCustomizer(customizer);
        }
        if (next != null && !next.isEmpty()) {
            for (KeyFactoryCustomizer keyFactoryCustomizer : next) {
                gen.addCustomizer(keyFactoryCustomizer);
            }
        }
        gen.setClassLoader(loader);
        return gen.create();
    }

    public KeyFactory create() {
            setNamePrefix(keyInterface.getName());
            return (KeyFactory)super.create(keyInterface.getName());
        }

super.create(keyInterface.getName()

 使用WeakHashMap缓存，以classLoader为key，value是ClassLoaderData

    private static volatile Map CACHE = new WeakHashMap();

    protected Object create(Object key) {
        try {
            ClassLoader loader = getClassLoader();
            Map cache = CACHE;
            ClassLoaderData data = cache.get(loader);
            if (data == null) {
                synchronized (AbstractClassGenerator.class) {
                    cache = CACHE;
                    data = cache.get(loader);
                    if (data == null) {
                        Map newCache = new WeakHashMap(cache);
                        data = new ClassLoaderData(loader);
                        newCache.put(loader, data);
                        CACHE = newCache;
                    }
                }
            }
            this.key = key;
            Object obj = data.get(this, getUseCache());
            if (obj instanceof Class) {
                return firstInstance((Class) obj);
            }
            return nextInstance(obj);
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        }
    }

我们看new ClassLoaderData()发生了什么

    public ClassLoaderData(ClassLoader classLoader) {
            if (classLoader == null) {
                throw new IllegalArgumentException("classLoader == null is not yet supported");
            }
            this.classLoader = new WeakReference(classLoader);
            Function load =
                    new Function() {
                        public Object apply(AbstractClassGenerator gen) {
                            //此处生成字节码
                            Class klass = gen.generate(ClassLoaderData.this);
                            return gen.wrapCachedClass(klass);
                        }
                    };
            generatedClasses = new LoadingCache(GET_KEY, load);
        }

Class klass = gen.generate(ClassLoaderData.this);

    protected Class generate(ClassLoaderData data) {
        Class gen;
        Object save = CURRENT.get();
        CURRENT.set(this);
        try {
            ClassLoader classLoader = data.getClassLoader();
            if (classLoader == null) {
                throw new IllegalStateException("ClassLoader is null while trying to define class " +
                        getClassName() + ". It seems that the loader has been expired from a weak reference somehow. " +
                        "Please file an issue at cglib's issue tracker.");
            }
            synchronized (classLoader) {
              //动态代理生成类名称
              String name = generateClassName(data.getUniqueNamePredicate());              
              data.reserveName(name);
              this.setClassName(name);
            }
            //有代理类直接加载
            if (attemptLoad) {
                try {
                    gen = classLoader.loadClass(getClassName());
                    return gen;
                } catch (ClassNotFoundException e) {
                    // ignore
                }
            }
            //生成字节码
            byte[] b = strategy.generate(this);
            String className = ClassNameReader.getClassName(new ClassReader(b));
            ProtectionDomain protectionDomain = getProtectionDomain();
            synchronized (classLoader) { // just in case
                //加载类，生成class对象
                if (protectionDomain == null) {
                    gen = ReflectUtils.defineClass(className, b, classLoader);
                } else {
                    gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain);
                }
            }
            return gen;
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        } finally {
            CURRENT.set(save);
        }
    }

类名生成规则，使用$和$$加哈希值，跟上面调试的代码一致。 

    public String getClassName(String prefix, String source, Object key, Predicate names) {
        if (prefix == null) {
            prefix = "net.sf.cglib.empty.Object";
        } else if (prefix.startsWith("java")) {
            prefix = "$" + prefix;
        }
        String base =
            prefix + "$$" + 
            source.substring(source.lastIndexOf('.') + 1) +
            getTag() + "$$" +
            Integer.toHexString(STRESS_HASH_CODE ? 0 : key.hashCode());
        String attempt = base;
        int index = 2;
        while (names.evaluate(attempt))
            attempt = base + "_" + index++;
        return attempt;
    }

下面看字节码生成类

    public byte[] generate(ClassGenerator cg) throws Exception {
        DebuggingClassWriter cw = getClassVisitor();
        transform(cg).generateClass(cw);
        return transform(cw.toByteArray());
    }


    public class DebuggingClassWriter extends ClassVisitor {
    public static final String DEBUG_LOCATION_PROPERTY = "cglib.debugLocation";
    //这里可以设置写文件的位置
    private static String debugLocation = System.getProperty("cglib.debugLocation");
    private static Constructor traceCtor;
    private String className;
    private String superName;

    public DebuggingClassWriter(int flags) {
        super(327680, new ClassWriter(flags));
    }

    public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
        this.className = name.replace('/', '.');
        this.superName = superName.replace('/', '.');
        super.visit(version, access, name, signature, superName, interfaces);
    }

    public String getClassName() {
        return this.className;
    }

    public String getSuperName() {
        return this.superName;
    }

    public byte[] toByteArray() {
        return (byte[])((byte[])AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                byte[] b = ((ClassWriter)DebuggingClassWriter.access$001(DebuggingClassWriter.this)).toByteArray();
                //如果有文件位置则写文件
                if (DebuggingClassWriter.debugLocation != null) {
                    String dirs = DebuggingClassWriter.this.className.replace('.', File.separatorChar);

                    try {
                        (new File(DebuggingClassWriter.debugLocation + File.separatorChar + dirs)).getParentFile().mkdirs();
                        File file = new File(new File(DebuggingClassWriter.debugLocation), dirs + ".class");
                        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));

                        try {
                            out.write(b);
                        } finally {
                            out.close();
                        }

                        if (DebuggingClassWriter.traceCtor != null) {
                            file = new File(new File(DebuggingClassWriter.debugLocation), dirs + ".asm");
                            out = new BufferedOutputStream(new FileOutputStream(file));

                            try {
                                ClassReader cr = new ClassReader(b);
                                PrintWriter pw = new PrintWriter(new OutputStreamWriter(out));
                                ClassVisitor tcv = (ClassVisitor)DebuggingClassWriter.traceCtor.newInstance(null, pw);
                                cr.accept(tcv, 0);
                                pw.flush();
                            } finally {
                                out.close();
                            }
                        }
                    } catch (Exception var17) {
                        throw new CodeGenerationException(var17);
                    }
                }

                return b;
            }
        }));
    }

可以通过

System.getProperty("cglib.debugLocation") 

System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "/home/xxx");

 通过设置可以写文件，写道指定的路径。

此处 通过写字节码的方式实现了EnhancerKey子类，实现相关功能。这里没有注册方法拦截器，因为是自己实现接口的实现类。

    public void generateClass(ClassVisitor v) {
            //继承父类EnhancerKey
            ClassEmitter ce = new ClassEmitter(v);
            
            Method newInstance = ReflectUtils.findNewInstance(keyInterface);
            if (!newInstance.getReturnType().equals(Object.class)) {
                throw new IllegalArgumentException("newInstance method must return Object");
            }

            Type[] parameterTypes = TypeUtils.getTypes(newInstance.getParameterTypes());
            //继承实现
            ce.begin_class(Constants.V1_2,
                           Constants.ACC_PUBLIC,
                           getClassName(),
                           KEY_FACTORY,
                           new Type[]{ Type.getType(keyInterface) },
                           Constants.SOURCE_FILE);
            EmitUtils.null_constructor(ce);
            EmitUtils.factory_method(ce, ReflectUtils.getSignature(newInstance));

            int seed = 0;
            CodeEmitter e = ce.begin_method(Constants.ACC_PUBLIC,
                                            TypeUtils.parseConstructor(parameterTypes),
                                            null);
            e.load_this();
            e.super_invoke_constructor();
            e.load_this();
            //属性
            List fieldTypeCustomizers = getCustomizers(FieldTypeCustomizer.class);
            for (int i = 0; i < parameterTypes.length; i++) {
                Type parameterType = parameterTypes[i];
                Type fieldType = parameterType;
                for (FieldTypeCustomizer customizer : fieldTypeCustomizers) {
                    fieldType = customizer.getOutType(i, fieldType);
                }
                seed += fieldType.hashCode();
                ce.declare_field(Constants.ACC_PRIVATE | Constants.ACC_FINAL,
                                 getFieldName(i),
                                 fieldType,
                                 null);
                e.dup();
                e.load_arg(i);
                for (FieldTypeCustomizer customizer : fieldTypeCustomizers) {
                    customizer.customize(e, i, parameterType);
                }
                e.putfield(getFieldName(i));
            }
            e.return_value();
            e.end_method();
            
            // hash code
            //方法
            e = ce.begin_method(Constants.ACC_PUBLIC, HASH_CODE, null);
            int hc = (constant != 0) ? constant : PRIMES[(int)(Math.abs(seed) % PRIMES.length)];
            int hm = (multiplier != 0) ? multiplier : PRIMES[(int)(Math.abs(seed * 13) % PRIMES.length)];
            e.push(hc);
            for (int i = 0; i < parameterTypes.length; i++) {
                e.load_this();
                e.getfield(getFieldName(i));
                EmitUtils.hash_code(e, parameterTypes[i], hm, customizers);
            }
            e.return_value();
            e.end_method();

            // equals
            e = ce.begin_method(Constants.ACC_PUBLIC, EQUALS, null);
            Label fail = e.make_label();
            e.load_arg(0);
            e.instance_of_this();
            e.if_jump(e.EQ, fail);
            for (int i = 0; i < parameterTypes.length; i++) {
                e.load_this();
                e.getfield(getFieldName(i));
                e.load_arg(0);
                e.checkcast_this();
                e.getfield(getFieldName(i));
                EmitUtils.not_equals(e, parameterTypes[i], fail, customizers);
            }
            e.push(1);
            e.return_value();
            e.mark(fail);
            e.push(0);
            e.return_value();
            e.end_method();

            // toString
            e = ce.begin_method(Constants.ACC_PUBLIC, TO_STRING, null);
            e.new_instance(Constants.TYPE_STRING_BUFFER);
            e.dup();
            e.invoke_constructor(Constants.TYPE_STRING_BUFFER);
            for (int i = 0; i < parameterTypes.length; i++) {
                if (i > 0) {
                    e.push(", ");
                    e.invoke_virtual(Constants.TYPE_STRING_BUFFER, APPEND_STRING);
                }
                e.load_this();
                e.getfield(getFieldName(i));
                EmitUtils.append_string(e, parameterTypes[i], EmitUtils.DEFAULT_DELIMITERS, customizers);
            }
            e.invoke_virtual(Constants.TYPE_STRING_BUFFER, TO_STRING);
            e.return_value();
            e.end_method();

            ce.end_class();
        }

 

3.2 示例的动态代理。

上面介绍了KeyFactory使用CGLIB的源码，下面是我们自己写的类实现动态代理

Object result = super.create(key)//key就是上面CGLIB动态创建的KeyFactory对象。

原理跟KeyFactory一样，只是generateClass实现不一样

核心：注册了方法拦截器，就是我们示例里面

public class HelloCGLibProxy implements MethodInterceptor

 

    public void generateClass(ClassVisitor v) throws Exception {
        Class sc = (superclass == null) ? Object.class : superclass;

        //final 类不能代理，因为CGLIB是通过继承实现子类的方式达到动态代理的目的
        if (TypeUtils.isFinal(sc.getModifiers()))
            throw new IllegalArgumentException("Cannot subclass final class " + sc.getName());
        //已定义的构造器
        List constructors = new ArrayList(Arrays.asList(sc.getDeclaredConstructors()));
        //剔除相同的构造器
        filterConstructors(sc, constructors);

        // Order is very important: must add superclass, then
        // its superclass chain, then each interface and
        // its superinterfaces.
        List actualMethods = new ArrayList();
        List interfaceMethods = new ArrayList();
        final Set forcePublic = new HashSet();
        getMethods(sc, interfaces, actualMethods, interfaceMethods, forcePublic);

        List methods = CollectionUtils.transform(actualMethods, new Transformer() {
            public Object transform(Object value) {
                Method method = (Method)value;
                int modifiers = Constants.ACC_FINAL
                    | (method.getModifiers()
                       & ~Constants.ACC_ABSTRACT
                       & ~Constants.ACC_NATIVE
                       & ~Constants.ACC_SYNCHRONIZED);
                if (forcePublic.contains(MethodWrapper.create(method))) {
                    modifiers = (modifiers & ~Constants.ACC_PROTECTED) | Constants.ACC_PUBLIC;
                }
                return ReflectUtils.getMethodInfo(method, modifiers);
            }
        });

        //设置父类
        ClassEmitter e = new ClassEmitter(v);
        //写继承实现关系
        if (currentData == null) {
        e.begin_class(Constants.V1_2,
                      Constants.ACC_PUBLIC,
                      getClassName(),
                      Type.getType(sc),
                      (useFactory ?
                       TypeUtils.add(TypeUtils.getTypes(interfaces), FACTORY) :
                       TypeUtils.getTypes(interfaces)),
                      Constants.SOURCE_FILE);
        } else {
            e.begin_class(Constants.V1_2,
                    Constants.ACC_PUBLIC,
                    getClassName(),
                    null,
                    new Type[]{FACTORY},
                    Constants.SOURCE_FILE);
        }
        List constructorInfo = CollectionUtils.transform(constructors, MethodInfoTransformer.getInstance());

        //属性
        e.declare_field(Constants.ACC_PRIVATE, BOUND_FIELD, Type.BOOLEAN_TYPE, null);
        e.declare_field(Constants.ACC_PUBLIC | Constants.ACC_STATIC, FACTORY_DATA_FIELD, OBJECT_TYPE, null);
        if (!interceptDuringConstruction) {
            e.declare_field(Constants.ACC_PRIVATE, CONSTRUCTED_FIELD, Type.BOOLEAN_TYPE, null);
        }
        e.declare_field(Constants.PRIVATE_FINAL_STATIC, THREAD_CALLBACKS_FIELD, THREAD_LOCAL, null);
        e.declare_field(Constants.PRIVATE_FINAL_STATIC, STATIC_CALLBACKS_FIELD, CALLBACK_ARRAY, null);
        if (serialVersionUID != null) {
            e.declare_field(Constants.PRIVATE_FINAL_STATIC, Constants.SUID_FIELD_NAME, Type.LONG_TYPE, serialVersionUID);
        }

        for (int i = 0; i < callbackTypes.length; i++) {
            e.declare_field(Constants.ACC_PRIVATE, getCallbackField(i), callbackTypes[i], null);
        }
        // This is declared private to avoid "public field" pollution
        e.declare_field(Constants.ACC_PRIVATE | Constants.ACC_STATIC, CALLBACK_FILTER_FIELD, OBJECT_TYPE, null);

        //定义方法
        if (currentData == null) {
            emitMethods(e, methods, actualMethods);
            emitConstructors(e, constructorInfo);
        } else {
            emitDefaultConstructor(e);
        }

        //定义方法拦截器，CGLIB动态代理功能依赖于方法拦截器实现
        emitSetThreadCallbacks(e);
        emitSetStaticCallbacks(e);
        emitBindCallbacks(e);

        if (useFactory || currentData != null) {
            int[] keys = getCallbackKeys();
            emitNewInstanceCallbacks(e);
            emitNewInstanceCallback(e);
            emitNewInstanceMultiarg(e, constructorInfo);
            emitGetCallback(e, keys);
            emitSetCallback(e, keys);
            emitGetCallbacks(e);
            emitSetCallbacks(e);
        }

        e.end_class();
    }

调试结果如下：

可以看出是Enhancer中生成了HelloService的代理类，此类事HelloService的子类。

4. 反编译代理类

设置属性

System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "xxx");

 有三个文件，中间那个就是我们的代理类

通过继承的方式来实现代理的 

优点：可以代理类，代理速度快

缺点：不能代理final类final方法，生成字节码很慢，生成3个类