cglib動態代理和jdk動態代理的區別與應用
1,引入
如果從一個Controller呼叫Service的非事務方法a,然後在a裡呼叫事務方法b,b事務生效嗎?
public void update() { updateActual(); int a = 1 / 0; } @Transactional public void updateActual() { WithHoldInfoVO vo = new WithHoldInfoVO(); vo.setId(18); vo.setStatus(5); withholdMapper.updateWithHoldInfo(vo); WithHoldInfoVO vo1 = new WithHoldInfoVO(); vo1.setId(27); vo1.setStatus(5); withholdMapper.updateWithHoldInfo(vo1); } |
形如這樣,如果從Controller層直接呼叫update方法,updateActual方法的事務可以生效嗎?如果不能,那麼如何才能使事務生效?
2,什麼是代理?
代理,簡單來說,就是代替處理,代替原有操作者去處理一件事。在Java中一般是2種,靜態代理和動態代理,動態代理又分為CGLIB和jdk自帶。
3,如何使用?
3.1靜態代理:
public class StaticProxy { public static void main(String[] args) { Singer singer = new Agent(new Star()); singer.sing(); } } /** * 代理實現,代理了歌星,唱歌的時候 會先在歌手唱歌之前收錢,然後再唱歌 */ class Agent implements Singer { Star s; public Agent(Star s) { super(); this.s = s; } @Override public void sing() { System.out.println("在歌手唱歌之前收錢...."); s.sing(); } } /** * 真實實現,一個歌星 */ class Star implements Singer { @Override public void sing() { System.out.println("Star Singing~~~"); } } /** * 最頂層介面 歌手 */ interface Singer { void sing(); } |
3.2 jdk動態代理
@SuppressWarnings("restriction") public class JavaProxyTest { public static void main(String[] args) throws Exception { JavaProxyInterface javaProxyInterface = new ConcreteClass(); JavaProxyInterface newJavaProxyInterface = (JavaProxyInterface) Proxy.newProxyInstance( JavaProxyTest.class.getClassLoader(), new Class[] { JavaProxyInterface.class }, new MyInvocationHandler(javaProxyInterface)); //這裡可以看到這個類以及被代理,在執行方法前會執行aopMethod()。這裡需要注意的是oneDay()方法和oneDayFinal()的區別。oneDayFinal的方法aopMethod執行1次,oneDay的aopMethod執行1次 newJavaProxyInterface.gotoSchool(); newJavaProxyInterface.gotoWork(); newJavaProxyInterface.oneDayFinal(); newJavaProxyInterface.oneDay(); } } /** * InvocationHandler 的一個實現,實際上處理代理的邏輯在這裡 */ class MyInvocationHandler implements InvocationHandler { JavaProxyInterface javaProxy; public MyInvocationHandler(JavaProxyInterface javaProxy) { this.javaProxy = javaProxy; } private void aopMethod() { System.out.println("before method"); } //繼承方法,代理時實際執行的犯法,如果要實現原方法,則需要呼叫method.invoke(javaProxy, args),這裡還呼叫了一個aopMethod(),可以類比於Spring中的切面before註解。 @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { aopMethod(); return method.invoke(javaProxy, args); } } /** * 需要一個最頂層介面,必須 */ interface JavaProxyInterface { void gotoSchool(); void gotoWork(); void oneDay(); void oneDayFinal(); } /** * 需要被代理的類,實現了頂層介面,非必須 */ class ConcreteClass implements JavaProxyInterface { @Override public void gotoSchool() { System.out.println("gotoSchool"); } @Override public void gotoWork() { System.out.println("gotoWork"); } @Override public void oneDay() { gotoSchool(); gotoWork(); } @Override public final void oneDayFinal() { gotoSchool(); gotoWork(); } } |
3.3 cglib 動態代理
public class CglibProxyTest { public static void main(String[] args) throws Exception { CglibTestSon CglibTestSon = new CglibTestSon(); Enhancer enhancer = new Enhancer(); Callback s = new MthdInvoker(CglibTestSon); enhancer.setSuperclass(CglibTestSon.class); Callback callbacks[] = new Callback[] { s }; enhancer.setCallbacks(callbacks); CglibTestSon CglibTestSon2 = (CglibTestSon) enhancer.create(); CglibTestSon2.gotoHome(); CglibTestSon2.gotoSchool(); ////這裡可以看到這個類以及被代理,在執行方法前會執行aopMethod()。這裡需要注意的是oneDay()方法和onedayFinal()的區別。onedayFinal的方法aopMethod執行2次,oneDay的aopMethod執行1次 ,注意這裡和jdk的代理的區別 CglibTestSon2.oneday(); CglibTestSon2.onedayFinal(); } } /** * 需要被代理的類,不需要實現頂層介面 */ class CglibTestSon { public CglibTestSon() { } public void gotoHome() { System.out.println("============gotoHome============"); } public void gotoSchool() { System.out.println("===========gotoSchool============"); } public void oneday() { gotoHome(); gotoSchool(); } public final void onedayFinal() { gotoHome(); gotoSchool(); } } /** * 可以類比於jdk動態代理中的InvocationHandler ,實際上被代理後重要的類,實際上後續執行的就是intercept裡的方法,如果需要執行原來的方法,則呼叫 method.invoke(s, args);這裡也加了一個aopMethod(); */ class MthdInvoker implements MethodInterceptor { private CglibTestSon s; public MthdInvoker(CglibTestSon s) { this.s = s; } private void aopMethod() { System.out.println("i am aopMethod"); } public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable { aopMethod(); Object a = method.invoke(s, args); return a; } } cglib 需要的maven配置: <dependencies> <dependency> <groupId>cglib</groupId> <artifactId>cglib</artifactId> <version>3.2.6</version> </dependency> </dependencies> |
4,區別
名稱 | 備註 |
---|---|
靜態代理 | 簡單,代理模式,是動態代理的理論基礎。常見使用在代理模式 |
jdk動態代理 |
需要有頂層接口才能使用,但是在只有頂層介面的時候也可以使用,常見是mybatis的mapper檔案是代理。 使用反射完成。使用了動態生成位元組碼技術。 |
cglib動態代理 | 可以直接代理類,使用位元組碼技術,不能對 final類進行繼承。使用了動態生成位元組碼技術。 |
5,底層怎麼實現呢?
都知道是動態代理是使用動態生成位元組碼技術生成了位元組碼,那麼生成的位元組碼有什麼區別呢?怎麼看生成的位元組碼呢?如何生成的位元組碼呢?
5.1 jdk底層實現
位元組碼最後是靠這一句來生成,
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(proxyName, interfaces); // proxyName 為類名,interfaces為頂層介面Class //如果需要看,可以將位元組碼寫入檔案進行觀察 File file = new File("D:/testProxy/Ddd.class"); FileOutputStream fileOutputStream = new FileOutputStream(file); fileOutputStream.write(bs); fileOutputStream.flush(); fileOutputStream.close(); |
自己觀察可以從Proxy.newProxyInstance( ClassLoader paramClassLoader, Class<?>[] paramArrayOfClass, InvocationHandler paramInvocationHandler)進行觀察,簡單來看就是先生成新的class檔案,然後載入到jvm中,然後使用反射,先用class取得他的構造方法,然後使用構造方法反射得到他的一個例項。
標紅的是最複雜的。然後cglib的實現原理基本一致,唯一的區別在於生成新的class檔案方式和結果不一樣。
5.2 cglib 底層實現
直接上最終生成位元組碼的程式碼。需要注意的是這裡要想執行這句話,必須在實現cglib動態代理的程式碼之後,否則取不到DefaultGeneratorStrategy的例項。
byte[] bs = DefaultGeneratorStrategy.INSTANCE.generate(enhancer); FileOutputStream fileOutputStream = new FileOutputStream("D:/testProxy/Cc.class"); fileOutputStream.write(bs); fileOutputStream.flush(); fileOutputStream.close(); |
跟蹤enhancer.create(); 這個程式碼可以看具體怎麼生成位元組碼,怎麼將位元組碼轉化為類。過程基本雷同於jdk,主要區別在於生成位元組碼的區別。
5.3 小結
這裡生成程式碼的過程中,都使用了快取,jdk自帶的使用了weakReference引用,而cglib使用的直接是 WeakHashMap,基本也類似。
6,生成的位元組碼到底是什麼樣子的呢?
6.1 cglib
// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package aaa; import java.lang.reflect.Method; import net.sf.cglib.core.ReflectUtils; import net.sf.cglib.core.Signature; import net.sf.cglib.proxy.Callback; import net.sf.cglib.proxy.Factory; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; public class CglibTestSon$$EnhancerByCGLIB$$3119e01d extends CglibTestSon implements Factory { private boolean CGLIB$BOUND; public static Object CGLIB$FACTORY_DATA; private static final ThreadLocal CGLIB$THREAD_CALLBACKS; private static final Callback[] CGLIB$STATIC_CALLBACKS; private MethodInterceptor CGLIB$CALLBACK_0; private static Object CGLIB$CALLBACK_FILTER; private static final Method CGLIB$gotoHome$0$Method; private static final MethodProxy CGLIB$gotoHome$0$Proxy; private static final Object[] CGLIB$emptyArgs; private static final Method CGLIB$gotoSchool$1$Method; private static final MethodProxy CGLIB$gotoSchool$1$Proxy; private static final Method CGLIB$oneday$2$Method; private static final MethodProxy CGLIB$oneday$2$Proxy; private static final Method CGLIB$equals$3$Method; private static final MethodProxy CGLIB$equals$3$Proxy; private static final Method CGLIB$toString$4$Method; private static final MethodProxy CGLIB$toString$4$Proxy; private static final Method CGLIB$hashCode$5$Method; private static final MethodProxy CGLIB$hashCode$5$Proxy; private static final Method CGLIB$clone$6$Method; private static final MethodProxy CGLIB$clone$6$Proxy; static void CGLIB$STATICHOOK2() { CGLIB$THREAD_CALLBACKS = new ThreadLocal(); CGLIB$emptyArgs = new Object[0]; Class var0 = Class.forName("com.rrc.finance.CglibTestSon$$EnhancerByCGLIB$$3119e01d"); Class var1; Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods()); CGLIB$equals$3$Method = var10000[0]; CGLIB$equals$3$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$3"); CGLIB$toString$4$Method = var10000[1]; CGLIB$toString$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$4"); CGLIB$hashCode$5$Method = var10000[2]; CGLIB$hashCode$5$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$5"); CGLIB$clone$6$Method = var10000[3]; CGLIB$clone$6$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$6"); var10000 = ReflectUtils.findMethods(new String[]{"gotoHome", "()V", "gotoSchool", "()V", "oneday", "()V"}, (var1 = Class.forName("com.rrc.finance.CglibTestSon")).getDeclaredMethods()); CGLIB$gotoHome$0$Method = var10000[0]; CGLIB$gotoHome$0$Proxy = MethodProxy.create(var1, var0, "()V", "gotoHome", "CGLIB$gotoHome$0"); CGLIB$gotoSchool$1$Method = var10000[1]; CGLIB$gotoSchool$1$Proxy = MethodProxy.create(var1, var0, "()V", "gotoSchool", "CGLIB$gotoSchool$1"); CGLIB$oneday$2$Method = var10000[2]; CGLIB$oneday$2$Proxy = MethodProxy.create(var1, var0, "()V", "oneday", "CGLIB$oneday$2"); } final void CGLIB$gotoHome$0() { super.gotoHome(); } public final void gotoHome() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { var10000.intercept(this, CGLIB$gotoHome$0$Method, CGLIB$emptyArgs, CGLIB$gotoHome$0$Proxy); } else { super.gotoHome(); } } final void CGLIB$gotoSchool$1() { super.gotoSchool(); } public final void gotoSchool() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { var10000.intercept(this, CGLIB$gotoSchool$1$Method, CGLIB$emptyArgs, CGLIB$gotoSchool$1$Proxy); } else { super.gotoSchool(); } } final void CGLIB$oneday$2() { super.oneday(); } public final void oneday() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { var10000.intercept(this, CGLIB$oneday$2$Method, CGLIB$emptyArgs, CGLIB$oneday$2$Proxy); } else { super.oneday(); } } final boolean CGLIB$equals$3(Object var1) { return super.equals(var1); } public final boolean equals(Object var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var2 = var10000.intercept(this, CGLIB$equals$3$Method, new Object[]{var1}, CGLIB$equals$3$Proxy); return var2 == null ? false : (Boolean)var2; } else { return super.equals(var1); } } final String CGLIB$toString$4() { return super.toString(); } public final String toString() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$4$Method, CGLIB$emptyArgs, CGLIB$toString$4$Proxy) : super.toString(); } final int CGLIB$hashCode$5() { return super.hashCode(); } public final int hashCode() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var1 = var10000.intercept(this, CGLIB$hashCode$5$Method, CGLIB$emptyArgs, CGLIB$hashCode$5$Proxy); return var1 == null ? 0 : ((Number)var1).intValue(); } else { return super.hashCode(); } } final Object CGLIB$clone$6() throws CloneNotSupportedException { return super.clone(); } protected final Object clone() throws CloneNotSupportedException { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? var10000.intercept(this, CGLIB$clone$6$Method, CGLIB$emptyArgs, CGLIB$clone$6$Proxy) : super.clone(); } public static MethodProxy CGLIB$findMethodProxy(Signature var0) { String var10000 = var0.toString(); switch(var10000.hashCode()) { case -1311123629: if (var10000.equals("gotoHome()V")) { return CGLIB$gotoHome$0$Proxy; } break; case -508378822: if (var10000.equals("clone()Ljava/lang/Object;")) { return CGLIB$clone$6$Proxy; } break; case 800823646: if (var10000.equals("gotoSchool()V")) { return CGLIB$gotoSchool$1$Proxy; } break; case 1826985398: if (var10000.equals("equals(Ljava/lang/Object;)Z")) { return CGLIB$equals$3$Proxy; } break; case 1913648695: if (var10000.equals("toString()Ljava/lang/String;")) { return CGLIB$toString$4$Proxy; } break; case 1984935277: if (var10000.equals("hashCode()I")) { return CGLIB$hashCode$5$Proxy; } break; case 2071325759: if (var10000.equals("oneday()V")) { return CGLIB$oneday$2$Proxy; } } return null; } public CglibTestSon$$EnhancerByCGLIB$$3119e01d() { CGLIB$BIND_CALLBACKS(this); } public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) { CGLIB$THREAD_CALLBACKS.set(var0); } public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) { CGLIB$STATIC_CALLBACKS = var0; } private static final void CGLIB$BIND_CALLBACKS(Object var0) { CglibTestSon$$EnhancerByCGLIB$$3119e01d var1 = (CglibTestSon$$EnhancerByCGLIB$$3119e01d)var0; if (!var1.CGLIB$BOUND) { var1.CGLIB$BOUND = true; Object var10000 = CGLIB$THREAD_CALLBACKS.get(); if (var10000 == null) { var10000 = CGLIB$STATIC_CALLBACKS; if (CGLIB$STATIC_CALLBACKS == null) { return; } } var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0]; } } public Object newInstance(Callback[] var1) { CGLIB$SET_THREAD_CALLBACKS(var1); CglibTestSon$$EnhancerByCGLIB$$3119e01d var10000 = new CglibTestSon$$EnhancerByCGLIB$$3119e01d(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Callback var1) { CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1}); CglibTestSon$$EnhancerByCGLIB$$3119e01d var10000 = new CglibTestSon$$EnhancerByCGLIB$$3119e01d(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) { CGLIB$SET_THREAD_CALLBACKS(var3); CglibTestSon$$EnhancerByCGLIB$$3119e01d var10000 = new CglibTestSon$$EnhancerByCGLIB$$3119e01d; switch(var1.length) { case 0: var10000.<init>(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; default: throw new IllegalArgumentException("Constructor not found"); } } public Callback getCallback(int var1) { CGLIB$BIND_CALLBACKS(this); MethodInterceptor var10000; switch(var1) { case 0: var10000 = this.CGLIB$CALLBACK_0; break; default: var10000 = null; } return var10000; } public void setCallback(int var1, Callback var2) { switch(var1) { case 0: this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2; default: } } public Callback[] getCallbacks() { CGLIB$BIND_CALLBACKS(this); return new Callback[]{this.CGLIB$CALLBACK_0}; } public void setCallbacks(Callback[] var1) { this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0]; } static { CGLIB$STATICHOOK2(); } } |
6.2 jdk
// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // import com.rrc.finance.JavaProxyInterface; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.lang.reflect.UndeclaredThrowableException; public final class Ddd extends Proxy implements JavaProxyInterface { private static Method m1; private static Method m5; private static Method m3; private static Method m2; private static Method m4; private static Method m6; private static Method m0; public Ddd(InvocationHandler var1) throws { super(var1); } public final boolean equals(Object var1) throws { try { return (Boolean)super.h.invoke(this, m1, new Object[]{var1}); } catch (RuntimeException | Error var3) { throw var3; } catch (Throwable var4) { throw new UndeclaredThrowableException(var4); } } public final void gotoSchool() throws { try { super.h.invoke(this, m5, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } public final void oneDay() throws { try { super.h.invoke(this, m3, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } 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 oneDayFinal() throws { try { super.h.invoke(this, m4, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } public final void gotoWork() throws { try { super.h.invoke(this, m6, (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); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object")); m5 = Class.forName("com.rrc.finance.JavaProxyInterface").getMethod("gotoSchool"); m3 = Class.forName("com.rrc.finance.JavaProxyInterface").getMethod("oneDay"); m2 = Class.forName("java.lang.Object").getMethod("toString"); m4 = Class.forName("com.rrc.finance.JavaProxyInterface").getMethod("oneDayFinal"); m6 = Class.forName("com.rrc.finance.JavaProxyInterface").getMethod("gotoWork"); m0 = Class.forName("java.lang.Object").getMethod("hashCode"); } catch (NoSuchMethodException var2) { throw new NoSuchMethodError(var2.getMessage()); } catch (ClassNotFoundException var3) { throw new NoClassDefFoundError(var3.getMessage()); } } } |
可以看到cglib是直接繼承了原有類,實現了Factory介面,而jdk是實現了自己的頂層介面,繼承了Proxy介面。這裡需要注意一下,這樣的話,按照類來找話,jdk就找不到他的實現了,因為他的實現類實際上是一個Proxy類,而不是他自己。
這句話通俗點的意思,可以看下一小節。
7,Spring中使用的是哪種代理呢?
先上結論,如果一個類有頂層介面,則預設使用jdk的動態代理來代理,如果直接是一個類,則使用cglib動態代理。 其次,如果沒有需要代理的方法,如所有方法都沒有@Transactional註解,Aop這種,則不會被代理。
問題來了,只說結論,沒有依據,怎麼讓人信服?
@Service public class TestServiceImpl implements TestService { @Transactional public void updateActual() { } } |
在這裡,我們實現一個Service,讓他實現一個頂層介面,然後我們如果在Controller裡使用
@Autowired
private TestServiceImpl testServiceImpl;
註解來注入,這時候會發現,啟動時報錯的。
報錯也很明顯:
The bean 'testServiceImpl' could not be injected as a 'com.rrc.finance.service.apply.TestServiceImpl' because it is a JDK dynamic proxy that implements: com.rrc.finance.service.apply.TestService |
改成 :@Autowired
private TestService testServiceImpl;
即可正常啟動。
證明動態代理生成的程式碼是一個 TestService 卻不是一個TestServiceImpl。使用的是jdk的動態代理。
這裡去掉事務註解和 去掉介面實現 自己可以再試一下。
8,會了這些就完了嗎?
在Spring的體系下,大多數的實現都在使用動態代理,我們可以通過他們優秀的原始碼來進行學習,來寫一個自己的專案。
例如:Mybatis的mapper代理,分頁外掛的代理實現。Spring的Aop,事務註解等。