Spring的AOP-Java的代理机制

AOP的基本思想

AOP的意思是面向方面编程，英文全称：Aspect Oriented Programming；AOP能够降低代码的耦合性，使得代码易于维护和重（chong）用,一个应用程序分为核心关注点和横切关注点。核心关注点和具体应用的功能相关，而横切关注点存在于整个系统的范围内。Spring的AOP是建立在Java的代理机制之上的。

Java的代理机制

通用的日志输出方法

============TimeBook类============== package com.gc.action.book; import org.apache.log4j.Level; import org.apache.log4j.Logger; public class TimeBook {     private  Logger logger = Logger.getLogger(this.getClass().getName());     public void doAuditing(String name){        System.out.println(logger);        logger.log(Level.INFO,name +"开始。。。");        System.out.println("=================");        logger.log(Level.INFO,name +"结束。。。");     } } =============TestTimeBook类============ package com.gc.action.book;   public class TestTimeBook {       public static void main(String[] args) {        TimeBook timeBook = new TimeBook();        timeBook.doAuditing("zx");     } } ========log4j.properties 配置文件=================== # Set root category priority to INFO and its only appender to CONSOLE. log4j.rootCategory=INFO, CONSOLE #log4j.rootCategory=INFO, CONSOLE, LOGFILE   # Set the enterprise logger category to FATAL and its only appender to CONSOLE. log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE   # CONSOLE is set to be a ConsoleAppender using a PatternLayout. log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender log4j.appender.CONSOLE.Threshold=INFO log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout log4j.appender.CONSOLE.layout.ConversionPattern=- %m%n   # LOGFILE is set to be a File appender using a PatternLayout. log4j.appender.LOGFILE=org.apache.log4j.FileAppender log4j.appender.LOGFILE.File=axis.log log4j.appender.LOGFILE.Append=true log4j.appender.LOGFILE.Threshold=INFO log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout log4j.appender.LOGFILE.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n ==================结果=============== org.apache.log4j.Logger@1ddc4ec2 - zx开始。。。 ================= - zx结束。。。

通过面向接口编程实现日志输出

============接口TimeBookInterface类==================== package com.gc.action.impl; public interface TimeBookInterface {     //通过面向接口编程实现日志输出     public void doAuditing(String name); } ============接口实现TimeBookImpl类======================= package com.gc.action.impl; public class TimeBookImpl implements TimeBookInterface {       @Override     public void doAuditing(String name) {        System.out.println(name+"实现");     } } ===========日志输出类TimeBookProxy ========================= package com.gc.action.impl;   import org.apache.log4j.Level; import org.apache.log4j.Logger; /**  * 日志输出  * @author yltd  *  */ public class TimeBookProxy {     private  Logger logger = Logger.getLogger(this.getClass().getName());     private TimeBookInterface timeBookInterface;     public TimeBookProxy(TimeBookInterface timeBookInterface){        this.timeBookInterface = timeBookInterface;     }     /**      * 实际业务处理      */     public void doAuditing(String name){        logger.log(Level.INFO, name+" 开始审批。");        timeBookInterface.doAuditing(name);        logger.log(Level.INFO, name+" 审批结束。");     } }  ==============测试类TestTimeBook ================================ package com.gc.action.impl; public class TestTimeBook {     public static void main(String[] args) {        TimeBookProxy  timeBookProxy = new TimeBookProxy(new TimeBookImpl());        timeBookProxy.doAuditing("zyx");     } } ================结果====================== - zyx 开始审批。 zyx实现 - zyx 审批结束。

使用Java的代理机制实现日志输出

====接口TestLogInterface ========================= package com.gc.action.javaLog; /**  * 接口  * @author yltd  *  */ public interface TestLogInterface {     //操作方法     public void doSameing(String name); } ========实现类TestLogImpl ======================== package com.gc.action.javaLog; /**  * 实现类  * @author yltd  *  */ public class TestLogImpl implements TestLogInterface {       @Override     public void doSameing(String name) {        System.out.println("name = "+name);           }   } ============日志信息代理类LogProxy ==================== package com.gc.action.javaLog;   import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import org.apache.log4j.Level; import org.apache.log4j.Logger;   /**  * 日志信息的代理类  * @author yltd  *  */ public class LogProxy implements InvocationHandler{     private Logger  logger =Logger.getLogger(this.getClass().getName());     private Object obj;         public Object dind(Object obj){        this.obj=obj;        return Proxy.newProxyInstance(obj.getClass().getClassLoader(), obj.getClass().getInterfaces(),this);     }         @Override     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        Object result =null;        logger.log(Level.INFO, args[0]+" 开始。。。");        result = method.invoke(obj, args);        logger.log(Level.INFO, args[0]+" 结束。。。");        return result;     } } ============测试类TestMain =========================== package com.gc.action.javaLog; /**  * 测试类  * @author yltd  *  */ import com.gc.action.javaLog.TestLogInterface; public class TestMain {       public static void main(String[] args) {        LogProxy lp =new LogProxy();        TestLogInterface tli =(TestLogInterface) lp.dind(new TestLogImpl());        tli.doSameing("zyx");     }   } ==========结果============ - zyx 开始。。。 name = zyx - zyx 结束。。。

总结：第一种方式，需要在每个类里都增加对输出日志信息的代码；第二种方式，虽然实现了业务逻辑与输出日志信息代码的分离，但还是必须依赖于固定的接口；第三种方式，真正实现了对输出日志信息代码的重用，并且不依赖于固定的接口实现。