java中动态代理实现机制
v前言:
代理模式是常用的java設(shè)計(jì)模式,它的特征是代理類與委托類有同樣的接口,代理類主要負(fù)責(zé)為委托類預(yù)處理消息、過(guò)濾消息、把消息轉(zhuǎn)發(fā)給委托類,以及事后處理消息等。代理類與委托類之間通常會(huì)存在關(guān)聯(lián)關(guān)系,一個(gè)代理類的對(duì)象與一個(gè)委托類的對(duì)象關(guān)聯(lián),代理類的對(duì)象本身并不真正實(shí)現(xiàn)服務(wù),而是通過(guò)調(diào)用委托類的對(duì)象的相關(guān)方法,來(lái)提供特定的服務(wù)。?
vJAVA各種動(dòng)態(tài)代理實(shí)現(xiàn)的比較
v接口
interface AddInterface{int add(int a, int b); }interface SubInterface{int sub(int a, int b); }v實(shí)現(xiàn)類
class Arithmetic implements AddInterface, SubInterface{@Overridepublic int sub(int a, int b) {return a-b;}@Overridepublic int add(int a, int b) {return a+b;} }v方式1: JDK自帶的動(dòng)態(tài)代理
v實(shí)現(xiàn)方式
Java在JDK1.3后引入的動(dòng)態(tài)代理機(jī)制,使我們可以在運(yùn)行期動(dòng)態(tài)的創(chuàng)建代理類。使用動(dòng)態(tài)代理實(shí)現(xiàn)AOP需要有四個(gè)角色:被代理的類,被代理類的接口,織入器,和InvocationHandler,而織入器使用接口反射機(jī)制生成一個(gè)代理類,然后在這個(gè)代理類中織入代碼。被代理的類是AOP里所說(shuō)的目標(biāo),InvocationHandler是切面,它包含了Advice和Pointcut。?
vInvocationHandler接口的實(shí)現(xiàn)
class JdkDPQueryHandler implements InvocationHandler{private Arithmetic real;public JdkDPQueryHandler(Arithmetic real){this.real = real;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {String methodName = method.getName();System.out.println(method);System.out.println("the method: " + methodName + "開(kāi)始, 參數(shù): "+Arrays.asList(args));Object result = method.invoke(real, args);System.out.println("the method: "+methodName+"結(jié)束, 結(jié)果: " + result);return result;} }v創(chuàng)建代理類并且調(diào)用代理類
public class Main{private static int a = 4, b = 2;public static Object createJDKProxy(Arithmetic real){Object proxyArithmetic = Proxy.newProxyInstance(real.getClass().getClassLoader(),real.getClass().getInterfaces(), new JdkDPQueryHandler(real)); return proxyArithmetic;}public static void main(String[] args){Arithmetic real = new Arithmetic();Object proxyArithmetic = createJDKProxy(real);((AddInterface)proxyArithmetic).add(a, b);((SubInterface)proxyArithmetic).sub(a, b);} }v方式2:動(dòng)態(tài)字節(jié)碼生成(cglib)
v實(shí)現(xiàn)方式
Enhancer和MethodInterceptor。Enhancer可以用來(lái)動(dòng)態(tài)的生成一個(gè)類,這個(gè)類可以繼承指定的一個(gè)類,實(shí)現(xiàn)指定的一些接口。同時(shí),Enhancer在生成一個(gè)類之前需要指定一個(gè)Callback,當(dāng)類方法調(diào)用時(shí),方法的執(zhí)行被分配給這個(gè)Callback,MethodInterceptor是一個(gè)使用比較多的繼承自Callback的接口,它只有一個(gè)方法聲明。v接口InvocationHandler(jdk中)和接口MethodInterceptor(cglib中)對(duì)比
public interface MethodInterceptor extends Callback { public Object intercept(Object obj, java.lang.reflect.Method method, Object[] args,MethodProxy proxy) throws Throwable; } public interface InvocationHandler { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable; } 從參數(shù)構(gòu)成上,methodInterceptor的輸入?yún)?shù)比Invocationhandler多1個(gè),其實(shí)前3個(gè)參數(shù)對(duì)象的含義與Invocationhandler的含義是相同的。 第一個(gè)參數(shù)表示調(diào)用方法來(lái)自哪個(gè)對(duì)象; 第二個(gè)參數(shù)表示調(diào)用方法的Method對(duì)象; 第三個(gè)參數(shù)表示此次調(diào)用的輸入?yún)?shù)列表; 多出來(lái)的參數(shù)是MethodProxy 類型的,它應(yīng)該是cglib生成用來(lái)代替Method對(duì)象的一個(gè)對(duì)象,使用MethodProxy比調(diào)用JDK自身的Method直接執(zhí)行方法效率會(huì)有提升。v實(shí)現(xiàn)1
MethodInterceptor接口的實(shí)現(xiàn)
class CglibDPQueryInterceptor implements MethodInterceptor{private Arithmetic real;public CglibDPQueryInterceptor(Arithmetic real){this.real = real;}@Overridepublic Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {String methodName = method.getName();System.out.println(method);System.out.println("the method: " + methodName + "開(kāi)始, 參數(shù): "+Arrays.asList(args));//Object result = method.invoke(real, args);//兩種方式都是可以得Object result = proxy.invoke(real, args);System.out.println("the method: "+methodName+"結(jié)束, 結(jié)果: " + result);return result;} }創(chuàng)建代理類并調(diào)用代理類
public class Main{private static int a = 4, b = 2;public static Object createCglibProxy(Arithmetic real){Enhancer enhancer = new Enhancer();enhancer.setCallback(new CglibDPQueryInterceptor(real));enhancer.setInterfaces(real.getClass().getInterfaces());return enhancer.create();}public static void main(String[] args){Arithmetic real = new Arithmetic(); Object proxyArithmetic = createCglibProxy(real); ((AddInterface)proxyArithmetic).add(a, b);((SubInterface)proxyArithmetic).sub(a, b);} }? 注意了,MethodProxy在對(duì)執(zhí)行函數(shù)的時(shí)候,提供了2個(gè)方法
public Object invoke (Object obj, Object[] args) throws Throwable public Object invokeSuper(Object obj, Object[] args) throws Throwable其中,javadoc上說(shuō)這個(gè)invoke()方法可以用于相同類中的其他對(duì)象的方法執(zhí)行,也就是說(shuō)這個(gè)方法中的obj需要傳入相同一個(gè)類的另一個(gè)對(duì)象(上述方法中就是傳入了Arithmetic類的不同對(duì)象),否則會(huì)進(jìn)入無(wú)限遞歸循環(huán)(測(cè)試之后還真是出現(xiàn)了StackOverflowError)。仔細(xì)的想一想就會(huì)發(fā)現(xiàn),public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy)中的target是實(shí)現(xiàn)的代理類對(duì)象,通過(guò)target調(diào)用add()方法時(shí)會(huì)觸發(fā)intercept()方法被調(diào)用,如果在intercept()方法中再調(diào)用method.invoke(target, args),就相當(dāng)于add()方法中又調(diào)用add()方法,導(dǎo)致無(wú)限的遞歸循環(huán)。但是如果執(zhí)行method.invoke(real, args)則不會(huì),因?yàn)閞eal和target是同一個(gè)類不同對(duì)象,real是真實(shí)邏輯主題,target是真實(shí)主題real的代理。
下面一個(gè)例子來(lái)模擬一下:
interface SolveInterface{void solve(); }class Real implements SolveInterface{public void solve(){System.out.println("Real Solve!");} }class Target extends Real{private Object obj;public void setObject(Object obj){this.obj = obj;}private void invoke(){try {Method method = SolveInterface.class.getMethod("solve", new Class[]{});method.invoke(obj, new Class[]{});} catch (Exception e) {e.printStackTrace();}}public void solve(){System.out.println("Target Solve!");invoke();} }public class Main{public static void main(String[] args) throws Exception{ Target target = new Target();target.setObject(new Real());//正確
//target.setObject(target);//發(fā)生循環(huán)調(diào)用target.solve();} }
其實(shí)Method的invoke()方法會(huì)根據(jù)obj的類型去調(diào)用對(duì)應(yīng)的solve()方法,也就是多態(tài)性。
v實(shí)現(xiàn)2
MethodInterceptor接口的實(shí)現(xiàn)
class CglibDPQueryInterceptor implements MethodInterceptor{@Overridepublic Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {String methodName = method.getName();System.out.println(method);System.out.println("the method: " + methodName + "開(kāi)始, 參數(shù): "+Arrays.asList(args));// 打印類信息 :target.getClass();省略Object result = proxy.invokeSuper(target, args);System.out.println("the method: "+methodName+"結(jié)束, 結(jié)果: " + result);return result;} }創(chuàng)建代理類并調(diào)用代理類
public class Main{private static int a = 4, b = 2; public static Object createCglibProxy(){Enhancer enhancer = new Enhancer();enhancer.setCallback(new CglibDPQueryInterceptor());enhancer.setSuperclass(Arithmetic.class);return enhancer.create();}public static void main(String[] args){Arithmetic real = new Arithmetic(); Object proxyArithmetic = createCglibProxy();((AddInterface)proxyArithmetic).add(a, b);((SubInterface)proxyArithmetic).sub(a, b);} }注意了,實(shí)現(xiàn)2中Enhancer 沒(méi)有設(shè)置接口,因?yàn)樵O(shè)置了Superclass了(也就是代理類的父類是Arithmetic),我們的代理類會(huì)繼承它,而Arithmetic已經(jīng)實(shí)現(xiàn)了我們的接口。為了證明這一點(diǎn),可以在MethodInterceptor的?intercept方法中打印?target.getClass()的類信息,你會(huì)發(fā)現(xiàn)cglib的兩種方式代理類的父類是不同的。如下:
(如果需要打印類信息代碼,請(qǐng)參考:http://www.cnblogs.com/hujunzheng/p/5132943.html)
實(shí)現(xiàn)1:
public class com.test.Arithmetic$$EnhancerByCGLIB$$4fa786eb extends java.lang.Object實(shí)現(xiàn)2:
public class com.test.Arithmetic$$EnhancerByCGLIB$$4fa786eb extends com.test.Arithmeticv方式3:javassist生成動(dòng)態(tài)代理(代理工廠創(chuàng)建?或者?動(dòng)態(tài)代碼創(chuàng)建)
Javassist是一個(gè)編輯字節(jié)碼的框架,可以讓你很簡(jiǎn)單地操作字節(jié)碼。它可以在運(yùn)行期定義或修改Class。使用Javassist實(shí)現(xiàn)AOP的原理是在字節(jié)碼加載前直接修改需要切入的方法。這比使用Cglib實(shí)現(xiàn)AOP更加高效,并且沒(méi)太多限制,實(shí)現(xiàn)原理如下圖:?
v實(shí)現(xiàn)1:
接口的實(shí)現(xiàn)
class JavassistDPQueryHandler implements MethodHandler{@Overridepublic Object invoke(Object target, Method method, Method proxy, Object[] args) throws Throwable {String methodName = method.getName();System.out.println(method);System.out.println("the method: " + methodName + "開(kāi)始, 參數(shù): "+Arrays.asList(args));Object result = proxy.invoke(target, args);System.out.println("the method: "+methodName+"結(jié)束, 結(jié)果: " + result);return result;} }創(chuàng)建代理類并調(diào)用代理類
public class Main{private static int a = 4, b = 2; public static Object createJavassistProxy() throws Exception{ProxyFactory factory = new ProxyFactory();factory.setSuperclass(Arithmetic.class);factory.setHandler(new JavassistDPQueryHandler());return factory.createClass().newInstance();}public static void main(String[] args) throws Exception{Arithmetic real = new Arithmetic();Object proxyArithmetic = createJavassistProxy();((AddInterface)proxyArithmetic).add(a, b);((SubInterface)proxyArithmetic).sub(a, b);} }注意:MethodHandler接口中invoke方法的定義,如下:
public Object invoke(Object target, Method method, Method proxy, Object[] args)method代表調(diào)用方法的Method對(duì)象,proxy是代理類產(chǎn)生并代替method的對(duì)象,否則用method.invoke(target, args)會(huì)產(chǎn)生無(wú)限循環(huán)調(diào)用。
v實(shí)現(xiàn)2:
(來(lái)自:http://cuishen.iteye.com/blog/421464),代碼注釋很詳細(xì),仔細(xì)研究一下就會(huì)懂了!
javassist使用動(dòng)態(tài)java代碼常見(jiàn)代理過(guò)程和前文的方法略有不同。javassist內(nèi)部可以通過(guò)動(dòng)態(tài)java代碼,生成字節(jié)碼。這種方式創(chuàng)建的動(dòng)態(tài)代理可以非常靈活,甚至可以在運(yùn)行時(shí)產(chǎn)生業(yè)務(wù)邏輯。
//自定義攔截器接口interface InterceptorHandler { /** * 調(diào)用動(dòng)態(tài)代理對(duì)象的方法將反射本方法,可在本方法實(shí)現(xiàn)中添加類似AOP的事前事后操作,只有在本方法體中加入如下代碼 * 被代理的方法才會(huì)被執(zhí)行,返回值將返回給代理最后返回給程序 * @param obj Object 被代理的對(duì)象 * @param method Method 被代理對(duì)象的方法 * @param args Object[] 被代理對(duì)象的方法的參數(shù) * @return Object 被代理對(duì)象的方法執(zhí)行后的返回值 * @throws Throwable */ public Object invoke(Object obj, Method method, Object[] args) throws Throwable; }
//攔截器的實(shí)現(xiàn) class InterceptorHandlerImpl implements InterceptorHandler{@Overridepublic Object invoke(Object obj, Method method, Object[] args) throws Throwable {String methodName = method.getName();System.out.println(method);System.out.println("the method: " + methodName + "開(kāi)始, 參數(shù): "+Arrays.asList(args));Object result = method.invoke(obj, args);System.out.println("the method: "+methodName+"結(jié)束, 結(jié)果: " + result);return result;} }class MyProxyImpl { /** 動(dòng)態(tài)代理類的類名后綴 */ private final static String PROXY_CLASS_NAME_SUFFIX = "$MyProxy_"; /** 攔截器接口 */ private final static String INTERCEPTOR_HANDLER_INTERFACE = "com.test.InterceptorHandler"; /** 動(dòng)態(tài)代理類的類名索引,防止類名重復(fù) */ private static int proxyClassIndex = 1; /** * 暴露給用戶的動(dòng)態(tài)代理接口,返回某個(gè)接口的動(dòng)態(tài)代理對(duì)象,注意本代理實(shí)現(xiàn)需和com.cuishen.myAop.InterceptorHandler攔截器配合 * 使用,即用戶要使用本動(dòng)態(tài)代理,需先實(shí)現(xiàn)com.cuishen.myAop.InterceptorHandler攔截器接口 * @param interfaceClassName String 要?jiǎng)討B(tài)代理的接口類名, e.g test.StudentInfoService * @param classToProxy String 要?jiǎng)討B(tài)代理的接口的實(shí)現(xiàn)類的類名, e.g test.StudentInfoServiceImpl * @param interceptorHandlerImplClassName String 用戶提供的攔截器接口的實(shí)現(xiàn)類的類名 * @return Object 返回某個(gè)接口的動(dòng)態(tài)代理對(duì)象 * @throws InstantiationException * @throws IllegalAccessException * @throws NotFoundException * @throws CannotCompileException * @throws ClassNotFoundException * @see com.cuishen.myAop.InterceptorHandler */ public static Object newProxyInstance(String interfaceClassName, String classToProxy, String interceptorHandlerImplClassName) throws InstantiationException, IllegalAccessException, NotFoundException, CannotCompileException, ClassNotFoundException { Class interfaceClass = Class.forName(interfaceClassName); Class interceptorHandlerImplClass = Class.forName(interceptorHandlerImplClassName); return dynamicImplementsInterface(classToProxy, interfaceClass, interceptorHandlerImplClass); } /** * 動(dòng)態(tài)實(shí)現(xiàn)要代理的接口 * @param classToProxy String 要?jiǎng)討B(tài)代理的接口的實(shí)現(xiàn)類的類名, e.g test.StudentInfoServiceImpl * @param interfaceClass Class 要?jiǎng)討B(tài)代理的接口類, e.g test.StudentInfoService * @param interceptorHandlerImplClass Class 用戶提供的攔截器接口的實(shí)現(xiàn)類 * @return Object 返回某個(gè)接口的動(dòng)態(tài)代理對(duì)象 * @throws NotFoundException * @throws CannotCompileException * @throws InstantiationException * @throws IllegalAccessException */ private static Object dynamicImplementsInterface(String classToProxy, Class interfaceClass, Class interceptorHandlerImplClass) throws NotFoundException, CannotCompileException, InstantiationException, IllegalAccessException { ClassPool cp = ClassPool.getDefault(); String interfaceName = interfaceClass.getName(); //動(dòng)態(tài)指定代理類的類名 String proxyClassName = interfaceName + PROXY_CLASS_NAME_SUFFIX + proxyClassIndex++; //要實(shí)現(xiàn)的接口的包名+接口名 String interfaceNamePath = interfaceName; CtClass ctInterface = cp.getCtClass(interfaceNamePath); CtClass cc = cp.makeClass(proxyClassName); cc.addInterface(ctInterface); Method [] methods = interfaceClass.getMethods(); for(int i = 0; i < methods.length; i++) { Method method = methods[i]; dynamicImplementsMethodsFromInterface(classToProxy, cc, method, interceptorHandlerImplClass, i); } return (Object)cc.toClass().newInstance(); } /** * 動(dòng)態(tài)實(shí)現(xiàn)接口里的方法 * @param classToProxy String 要?jiǎng)討B(tài)代理的接口的實(shí)現(xiàn)類的類名, e.g test.StudentInfoServiceImpl * @param implementer CtClass 動(dòng)態(tài)代理類的包裝 * @param methodToImpl Method 動(dòng)態(tài)代理類里面要實(shí)現(xiàn)的接口方法的包裝 * @param interceptorClass Class 用戶提供的攔截器實(shí)現(xiàn)類 * @param methodIndex int 要實(shí)現(xiàn)的方法的索引 * @throws CannotCompileException */ private static void dynamicImplementsMethodsFromInterface(String classToProxy, CtClass implementer, Method methodToImpl, Class interceptorClass, int methodIndex) throws CannotCompileException { String methodCode = generateMethodCode(classToProxy, methodToImpl, interceptorClass, methodIndex); CtMethod cm = CtNewMethod.make(methodCode, implementer); implementer.addMethod(cm); } /** * 動(dòng)態(tài)組裝方法體,當(dāng)然代理里面的方法實(shí)現(xiàn)并不是簡(jiǎn)單的方法拷貝,而是反射調(diào)用了攔截器里的invoke方法,并將接收到的參數(shù)進(jìn)行傳遞 * @param classToProxy String 要?jiǎng)討B(tài)代理的接口的實(shí)現(xiàn)類的類名, e.g test.StudentInfoServiceImpl * @param methodToImpl Method 動(dòng)態(tài)代理類里面要實(shí)現(xiàn)的接口方法的包裝 * @param interceptorClass Class 用戶提供的攔截器實(shí)現(xiàn)類 * @param methodIndex int 要實(shí)現(xiàn)的方法的索引 * @return String 動(dòng)態(tài)組裝的方法的字符串 */ private static String generateMethodCode(String classToProxy, Method methodToImpl, Class interceptorClass, int methodIndex) { String methodName = methodToImpl.getName(); String methodReturnType = methodToImpl.getReturnType().getName(); Class[] parameters = methodToImpl.getParameterTypes(); Class[] exceptionTypes = methodToImpl.getExceptionTypes(); StringBuffer exceptionBuffer = new StringBuffer(); //組裝方法的Exception聲明 if(exceptionTypes.length > 0) exceptionBuffer.append(" throws "); for(int i = 0; i < exceptionTypes.length; i++) { if(i != exceptionTypes.length - 1) exceptionBuffer.append(exceptionTypes[i].getName()).append(","); else exceptionBuffer.append(exceptionTypes[i].getName()); } StringBuffer parameterBuffer = new StringBuffer(); //組裝方法的參數(shù)列表 for(int i = 0; i < parameters.length; i++) { Class parameter = parameters[i]; String parameterType = parameter.getName(); //動(dòng)態(tài)指定方法參數(shù)的變量名 String refName = "a" + i; if(i != parameters.length - 1) parameterBuffer.append(parameterType).append(" " + refName).append(","); else parameterBuffer.append(parameterType).append(" " + refName); } StringBuffer methodDeclare = new StringBuffer(); //方法聲明,由于是實(shí)現(xiàn)接口的方法,所以是public methodDeclare.append("public ").append(methodReturnType).append(" ").append(methodName).append("(").append(parameterBuffer).append(")").append(exceptionBuffer).append(" {\n"); String interceptorImplName = interceptorClass.getName(); //方法體 methodDeclare.append(INTERCEPTOR_HANDLER_INTERFACE).append(" interceptor = new ").append(interceptorImplName).append("();\n"); //反射調(diào)用用戶的攔截器接口 methodDeclare.append("Object returnObj = interceptor.invoke(Class.forName(\"" + classToProxy + "\").newInstance(), Class.forName(\"" + classToProxy + "\").getMethods()[" + methodIndex + "], "); //傳遞方法里的參數(shù) if(parameters.length > 0) methodDeclare.append("new Object[]{"); for(int i = 0; i < parameters.length; i++) { //($w) converts from a primitive type to the corresponding wrapper type: e.g. //Integer i = ($w)5; if(i != parameters.length - 1) methodDeclare.append("($w)a" + i + ","); else methodDeclare.append("($w)a" + i); } if(parameters.length > 0) methodDeclare.append("});\n"); else methodDeclare.append("null);\n"); //對(duì)調(diào)用攔截器的返回值進(jìn)行包裝 if(methodToImpl.getReturnType().isPrimitive()) { if(methodToImpl.getReturnType().equals(Boolean.TYPE)) methodDeclare.append("return ((Boolean)returnObj).booleanValue();\n"); else if(methodToImpl.getReturnType().equals(Integer.TYPE)) methodDeclare.append("return ((Integer)returnObj).intValue();\n"); else if(methodToImpl.getReturnType().equals(Long.TYPE)) methodDeclare.append("return ((Long)returnObj).longValue();\n"); else if(methodToImpl.getReturnType().equals(Float.TYPE)) methodDeclare.append("return ((Float)returnObj).floatValue();\n"); else if(methodToImpl.getReturnType().equals(Double.TYPE)) methodDeclare.append("return ((Double)returnObj).doubleValue();\n"); else if(methodToImpl.getReturnType().equals(Character.TYPE)) methodDeclare.append("return ((Character)returnObj).charValue();\n"); else if(methodToImpl.getReturnType().equals(Byte.TYPE)) methodDeclare.append("return ((Byte)returnObj).byteValue();\n"); else if(methodToImpl.getReturnType().equals(Short.TYPE)) methodDeclare.append("return ((Short)returnObj).shortValue();\n"); } else { methodDeclare.append("return (" + methodReturnType + ")returnObj;\n"); } methodDeclare.append("}"); System.out.println(methodDeclare.toString()); return methodDeclare.toString(); } } public class Main{ public static void main(String[] args) throws Exception{
//分別對(duì)應(yīng) 代理類要實(shí)現(xiàn)的接口類名, 需要代理類的類名, 用戶自定義攔截器實(shí)現(xiàn)類的類名Object proxyArithmetic = MyProxyImpl.newProxyInstance("com.test.ArithmeticInterface", "com.test.Arithmetic",
"com.test.InterceptorHandlerImpl");((ArithmeticInterface)proxyArithmetic).add(a, b);((ArithmeticInterface)proxyArithmetic).sub(a, b); } }
打印一下動(dòng)態(tài)實(shí)現(xiàn)接口的代碼如下:
public int add(int a0,int a1) { com.test.InterceptorHandler interceptor = new com.test.InterceptorHandlerImpl(); Object returnObj = interceptor.invoke(Class.forName("com.test.Arithmetic").newInstance(), Class.forName("com.test.Arithmetic").getMethods()[0], new Object[]{($w)a0,($w)a1}); return ((Integer)returnObj).intValue(); } public int sub(int a0,int a1) { com.test.InterceptorHandler interceptor = new com.test.InterceptorHandlerImpl(); Object returnObj = interceptor.invoke(Class.forName("com.test.Arithmetic").newInstance(), Class.forName("com.test.Arithmetic").getMethods()[1], new Object[]{($w)a0,($w)a1}); return ((Integer)returnObj).intValue(); }?
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