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1，引入

如果從一個Controller調用Service的非事務方法a,然后在a里調用事務方法b，b事務生效嗎？

?public void update() {updateActual();int a = 1 / 0;}@Transactionalpublic 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層直接調用update方法，updateActual方法的事務可以生效嗎？如果不能，那么如何才能使事務生效？

2，什么是代理？

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。

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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，然后再唱歌 */ class Agent implements Singer {Star s;public Agent(Star s) {super();this.s = s;}@Overridepublic 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 {@Overridepublic void sing() {System.out.println("Star Singing~~~");} } /** * 最頂層接口 歌手 */ interface Singer {void sing(); }

3.2 jdk動態代理

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@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));//這里可以看到這個類以及被代理，在執行方法前會執行aopMethod（）。這里需要注意的是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里 */ 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，則需要調用method.invoke(javaProxy, args)，這里還調用了一個aopMethod(),可以類比于Spring中的切面before注解。@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {aopMethod();return method.invoke(javaProxy, args);} } /** * 需要一個最頂層接口，必須 */ interface JavaProxyInterface {void gotoSchool();void gotoWork();void oneDay();void oneDayFinal(); } /** * 需要被代理的類，實現了頂層接口，非必須 */ class ConcreteClass implements JavaProxyInterface {@Overridepublic void gotoSchool() {System.out.println("gotoSchool");}@Overridepublic void gotoWork() {System.out.println("gotoWork");}@Overridepublic void oneDay() {gotoSchool();gotoWork();}@Overridepublic 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();這里可以看到這個類以及被代理，在執行方法前會執行aopMethod（）。這里需要注意的是oneDay（）方法和onedayFinal（）的區別。onedayFinal的方法aopMethod執行2次，oneDay的aopMethod執行1次 ,注意這里和jdk的代理的區別CglibTestSon2.oneday();CglibTestSon2.onedayFinal();} } /** * 需要被代理的類，不需要實現頂層接口 */ 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();} } /** * 可以類比于jdk動態代理中的InvocationHandler ，實際上被代理后重要的類，實際上后續執行的就是intercept里的方法，如果需要執行原來的方法，則調用 method.invoke(s, args);這里也加了一個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

名稱備注

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，但是在只有頂層接口的時候也可以使用，常見是mybatis的mapper文件是代理。 使用反射完成。使用了動態生成字節碼技術。
cglib動態代理	可以直接代理類，使用字節碼技術，不能對?final類進行繼承。使用了動態生成字節碼技術。

5，底層怎么實現呢？

都知道是動態代理是使用動態生成字節碼技術生成了字節碼，那么生成的字節碼有什么區別呢？怎么看生成的字節碼呢？如何生成的字節碼呢？

5.1 jdk底層實現

字節碼最后是靠這一句來生成，

byte[] proxyClassFile = ProxyGenerator.generateProxyClass(proxyName, interfaces); // proxyName 為類名，interfaces為頂層接口Class //如果需要看，可以將字節碼寫入文件進行觀察 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文件，然后加載到jvm中，然后使用反射，先用class取得他的構造方法，然后使用構造方法反射得到他的一個實例。

標紅的是最復雜的。然后cglib的實現原理基本一致，唯一的區別在于生成新的class文件方式和結果不一樣。

5.2 cglib 底層實現

直接上最終生成字節碼的代碼。需要注意的是這里要想執行這句話，必須在實現cglib動態代理的代碼之后，否則取不到DefaultGeneratorStrategy的實例。

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(); 這個代碼可以看具體怎么生成字節碼，怎么將字節碼轉化為類。過程基本雷同于jdk,主要區別在于生成字節碼的區別。

5.3 小結

這里生成代碼的過程中，都使用了緩存，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，生成的字節碼到底是什么樣子的呢？

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接口，而jdk是實現了自己的頂層接口，繼承了Proxy接口。這里需要注意一下，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，如果一個類有頂層接口，則默認使用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注解，Aop這種，則不會被代理。

問題來了，只說結論，沒有依據，怎么讓人信服？

@Service public class TestServiceImpl implements TestService {@Transactionalpublic void updateActual() {}}

在這里，我們實現一個Service，讓他實現一個頂層接口，然后我們如果在Controller里使用

@Autowired
private TestServiceImpl testServiceImpl;

注解來注入，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代碼是一個? TestService 卻不是一個TestServiceImpl。使用的是jdk的動態代理。

這里去掉事務注解和 去掉接口實現 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源碼來進行學習，來寫一個自己的項目。

例如：Mybatis的mapper代理，分頁插件的代理實現。Spring的Aop，事務注解等。

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