都说 Cglib 创建的动态代理的运行性能比 JDK 动态代理能高出大概 10 倍，今日抱着怀疑精神验证了一下，发现情况有所不同，遂贴出实验结果，以供参考和讨论。
代码很简单，首先，定义一个 Test 接口，和一个实现 TestImpl 。Test 接口仅定义一个方法 test，对传入的 int 参数加 1 后返回。代码如下：
package my.test; public interface Test { public int test(int i); }
package my.test; public class TestImpl implements Test{ public int test(int i) { return i+1; } }
然后，定义了三种代理的实现：装饰者模式实现的代理(decorator)，JDK 动态代理(dynamic proxy) 和 Cglib 动态代理 (cglib proxy)。代码如下：
package my.test; public class DecoratorTest implements Test{ private Test target; public DecoratorTest(Test target) { this.target = target; } public int test(int i) { return target.test(i); } }
package my.test; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; public class DynamicProxyTest implements InvocationHandler { private Test target; private DynamicProxyTest(Test target) { this.target = target; } public static Test newProxyInstance(Test target) { return (Test) Proxy .newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class<?>[] { Test.class }, new DynamicProxyTest(target)); } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(target, args); } }
package my.test; import java.lang.reflect.Method; import net.sf.cglib.proxy.Enhancer; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; public class CglibProxyTest implements MethodInterceptor { private CglibProxyTest() { } public static <T extends Test> Test newProxyInstance(Class<T> targetInstanceClazz){ Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(targetInstanceClazz); enhancer.setCallback(new CglibProxyTest()); return (Test) enhancer.create(); } public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable { return proxy.invokeSuper(obj, args); } }
以 TestImpl 的调用耗时作为基准，对比通过其它三种代理进行调用的耗时。测试代码如下：
package my.test; import java.util.LinkedHashMap; import java.util.Map; public class ProxyPerfTester { public static void main(String[] args) { //创建测试对象； Test nativeTest = new TestImpl(); Test decorator = new DecoratorTest(nativeTest); Test dynamicProxy = DynamicProxyTest.newProxyInstance(nativeTest); Test cglibProxy = CglibProxyTest.newProxyInstance(TestImpl.class); //预热一下； int preRunCount = 10000; runWithoutMonitor(nativeTest, preRunCount); runWithoutMonitor(decorator, preRunCount); runWithoutMonitor(cglibProxy, preRunCount); runWithoutMonitor(dynamicProxy, preRunCount); //执行测试； Map<String, Test> tests = new LinkedHashMap<String, Test>(); tests.put("Native ", nativeTest); tests.put("Decorator", decorator); tests.put("Dynamic ", dynamicProxy); tests.put("Cglib ", cglibProxy); int repeatCount = 3; int runCount = 1000000; runTest(repeatCount, runCount, tests); runCount = 50000000; runTest(repeatCount, runCount, tests); } private static void runTest(int repeatCount, int runCount, Map<String, Test> tests){ System.out.println(String.format(" ==================== run test : [repeatCount=%s] [runCount=%s] [java.version=%s] ====================", repeatCount, runCount, System.getProperty("java.version"))); for (int i = 0; i < repeatCount; i++) { System.out.println(String.format(" --------- test : [%s] ---------", (i+1))); for (String key : tests.keySet()) { runWithMonitor(tests.get(key), runCount, key); } } } private static void runWithoutMonitor(Test test, int runCount) { for (int i = 0; i < runCount; i++) { test.test(i); } } private static void runWithMonitor(Test test, int runCount, String tag) { long start = System.currentTimeMillis(); for (int i = 0; i < runCount; i++) { test.test(i); } long end = System.currentTimeMillis(); System.out.println("["+tag + "] Elapsed Time:" + (end-start) + "ms"); } }
测试用例分别在 jdk6、 jdk7、jdk8 下进行了测试，每次测试分别以 1,000,000 和 50,000,000 循环次数调用 test 方法，并重复3次。
- jdk6 下的测试结果如下：
==================== run test : [repeatCount=3] [runCount=1000000] [java.version=1.6.0_45] ==================== --------- test : [1] --------- [Native ] Elapsed Time:2ms [Decorator] Elapsed Time:12ms [Dynamic ] Elapsed Time:31ms [Cglib ] Elapsed Time:31ms --------- test : [2] --------- [Native ] Elapsed Time:7ms [Decorator] Elapsed Time:7ms [Dynamic ] Elapsed Time:31ms [Cglib ] Elapsed Time:27ms --------- test : [3] --------- [Native ] Elapsed Time:7ms [Decorator] Elapsed Time:6ms [Dynamic ] Elapsed Time:23ms [Cglib ] Elapsed Time:29ms ==================== run test : [repeatCount=3] [runCount=50000000] [java.version=1.6.0_45] ==================== --------- test : [1] --------- [Native ] Elapsed Time:212ms [Decorator] Elapsed Time:226ms [Dynamic ] Elapsed Time:1054ms [Cglib ] Elapsed Time:830ms --------- test : [2] --------- [Native ] Elapsed Time:184ms [Decorator] Elapsed Time:222ms [Dynamic ] Elapsed Time:1020ms [Cglib ] Elapsed Time:826ms --------- test : [3] --------- [Native ] Elapsed Time:184ms [Decorator] Elapsed Time:208ms [Dynamic ] Elapsed Time:979ms [Cglib ] Elapsed Time:832ms
测试结果表明：jdk6 下，在运行次数较少的情况下，jdk动态代理与 cglib 差距不明显，甚至更快一些；而当调用次数增加之后， cglib 表现稍微更快一些，然而仅仅是“稍微”好一些，远没达到 10 倍差距。
- jdk7 下的测试结果如下：
==================== run test : [repeatCount=3] [runCount=1000000] [java.version=1.7.0_60] ==================== --------- test : [1] --------- [Native ] Elapsed Time:2ms [Decorator] Elapsed Time:12ms [Dynamic ] Elapsed Time:19ms [Cglib ] Elapsed Time:26ms --------- test : [2] --------- [Native ] Elapsed Time:3ms [Decorator] Elapsed Time:5ms [Dynamic ] Elapsed Time:17ms [Cglib ] Elapsed Time:20ms --------- test : [3] --------- [Native ] Elapsed Time:4ms [Decorator] Elapsed Time:4ms [Dynamic ] Elapsed Time:13ms [Cglib ] Elapsed Time:27ms ==================== run test : [repeatCount=3] [runCount=50000000] [java.version=1.7.0_60] ==================== --------- test : [1] --------- [Native ] Elapsed Time:208ms [Decorator] Elapsed Time:210ms [Dynamic ] Elapsed Time:551ms [Cglib ] Elapsed Time:923ms --------- test : [2] --------- [Native ] Elapsed Time:238ms [Decorator] Elapsed Time:210ms [Dynamic ] Elapsed Time:483ms [Cglib ] Elapsed Time:872ms --------- test : [3] --------- [Native ] Elapsed Time:217ms [Decorator] Elapsed Time:208ms [Dynamic ] Elapsed Time:494ms [Cglib ] Elapsed Time:881ms
测试结果表明：jdk7 下，情况发生了逆转！在运行次数较少（1,000,000）的情况下，jdk动态代理比 cglib 快了差不多30%；而当调用次数增加之后(50,000,000)， 动态代理比 cglib 快了接近1倍。
接下来再看看jdk8下的表现如何。
- jdk8 下的测试结果如下：
==================== run test : [repeatCount=3] [runCount=1000000] [java.version=1.8.0_05] ==================== --------- test : [1] --------- [Native ] Elapsed Time:5ms [Decorator] Elapsed Time:11ms [Dynamic ] Elapsed Time:27ms [Cglib ] Elapsed Time:52ms --------- test : [2] --------- [Native ] Elapsed Time:4ms [Decorator] Elapsed Time:6ms [Dynamic ] Elapsed Time:11ms [Cglib ] Elapsed Time:24ms --------- test : [3] --------- [Native ] Elapsed Time:4ms [Decorator] Elapsed Time:5ms [Dynamic ] Elapsed Time:9ms [Cglib ] Elapsed Time:26ms ==================== run test : [repeatCount=3] [runCount=50000000] [java.version=1.8.0_05] ==================== --------- test : [1] --------- [Native ] Elapsed Time:194ms [Decorator] Elapsed Time:211ms [Dynamic ] Elapsed Time:538ms [Cglib ] Elapsed Time:965ms --------- test : [2] --------- [Native ] Elapsed Time:194ms [Decorator] Elapsed Time:214ms [Dynamic ] Elapsed Time:503ms [Cglib ] Elapsed Time:969ms --------- test : [3] --------- [Native ] Elapsed Time:190ms [Decorator] Elapsed Time:209ms [Dynamic ] Elapsed Time:495ms [Cglib ] Elapsed Time:939ms
测试结果表明：jdk8 下，延续了 JDK7 下的惊天大逆转！不过还观察另外有一个细微的变化，从绝对值来看 cglib 在 jdk8 下的表现似乎比 jdk7 还要差一点点，尽管只是一点点，但经过反复多次的执行仍然是这个趋势（注：这个趋势的结论并不严谨，只是捎带一提，如需得出结论还需进行更多样的对比实验）。
结论：从 jdk6 到 jdk7、jdk8 ，动态代理的性能得到了显著的提升，而 cglib 的表现并未跟上，甚至可能会略微下降。传言的 cglib 比 jdk动态代理高出 10 倍的情况也许是出现在更低版本的 jdk 上吧。
以上测试用例虽然简单，但揭示了 jdk 版本升级可能会带来一些新技术改变，会使我们以前的经验失效。放在真实业务场景下时，还需要按照实际情况进行测试后才能得出特定于场景的结论。
总之，实践出真知，还要与时俱进地去检视更新一些以往经验。
注：上述实验中 cglib 的版本是 3.1 。