(tng) (tng) (tng) 什么是AOPQ?/p>
(tng) (tng) (tng) 一个方面（aspect)是一个共有的Ҏ(gu)，h此代表性的有：(x)横向分离的方法，c，对象层次或者实体对象模型。它们看h应该是组合在一L(fng)Q但是在AOP里面你不用像以前面对对象QOOQ那hl织它们?jin)?/p>
(tng) (tng) (tng) 在传lJAVA中要加入计算旉的代码到你的应用中，你必L以下方式Q?/p>
public class BankAccountDAO{
(tng)public void withdraw(double amount){
(tng) long startTime = System.currentTimeMillis();
(tng) try (tng) {
(tng) (tng) (tng) // Actual method body...
(tng) }
(tng) finally (tng) {
(tng) (tng) (tng) long endTime = System.currentTimeMillis() - startTime;
(tng) (tng) (tng) System.out.println("withdraw took: " (tng) (tng) endTime);
(tng) }
(tng)}
}
(tng) (tng) (tng) 我们可以列Dq里面存在的几个问题Q?/p>
(tng) (tng) (tng) 1。如果你要在每个你的Ҏ(gu)中都加入q样的代理，无疑是十分糟p的Q特别是有try/catchq样的语句?/p>
(tng) (tng) (tng) 2。这里有很多代码都不是你真实需要用到的Q这样就使你的程序代码十分臃肿，读v来也十分困难。而且你不得不把你的代码放在try里面......
(tng) (tng) (tng)
(tng) (tng) (tng) 3。如果你要扩展这D代码，我们可以遇见到那是十分困难的工作?/p>
(tng) (tng) (tng) 所以可见，q样的代码是十分难于l护Q扩展和l承的，因ؓ(f)在这里面有很多东西分散了(jin)你对你这D代码真正要实现的东西的注意力。而且q只不过是一D|单的例子Q在真正的OOP中是很难实现对以上代码更好的表现Ҏ(gu)的?/p>
(tng) (tng) (tng) 面对斚w~程可以分离你的q些功能性，可以让你增加行ؓ(f)来围l你的功能代码。例如上面的QAOP可以在执行你自己的代码前你可以控制执行其它的功能?/p>
(tng) (tng) (tng) 所有实现AOP的框枉有两U方式：(x)l装x(chng)??a programmatic construct(~程实现)
(tng) (tng) (tng) JBOSS的一个横向切入关注点
01. public class Metrics implements org.jboss.aop.Interceptor
02. {
03. (tng) (tng) public Object invoke(Invocation invocation) throws Throwable
04. (tng) (tng) {
05. (tng) (tng) long startTime = System.currentTimeMillis();
06. (tng) (tng) try
07. (tng) (tng) {
08. (tng) (tng) (tng) (tng) return invocation.invokeNext();
09. (tng) (tng) }
10. (tng) (tng) finally
11. (tng) (tng) {
12. (tng) (tng) (tng) (tng) long endTime = System.currentTimeMillis() - startTime;
13. (tng) (tng) (tng) (tng) java.lang.reflect.Method m = ((MethodInvocation)invocation).method;
14. (tng) (tng) (tng) (tng) System.out.println("method " (tng) (tng) m.toString() (tng) (tng) " time: " (tng) (tng) endTime (tng) (tng) "ms");
15. (tng) (tng) }
16. (tng) }
17. }
(tng) (tng) (tng) 真正实现的功能代码是?行调用了(jin)Q这是实现?jin)组装关注点Q之成Z(jin)一个方面。这让我们在以后扩展实际功能的时候就十分方便?jin)，只需要去修改具体的实现方法，而不用去兛_(j)其它x(chng)点了(jin)?/p>
(tng) (tng) (tng) JBOOS中具体应用这个方?/p>
(tng) (tng) (tng) 需要定义一个切入点(pointcuts)Q全部通过政则表达式来实现?/p>
(tng) (tng) (tng) Listing Three: Defining a pointcut in JBoss AOP
1. <bind pointcut="public void com.mc.BankAccountDAO->withdraw(double amount)">
2. (tng) (tng) (tng) (tng) <interceptor class="com.mc.Metrics"/>
3. </bind >
4. <bind pointcut="* com.mc.billing.*->*(..)">
5. (tng) (tng) (tng) (tng) <interceptor class="com.mc.Metrics"/>
6. </bind >
(tng) (tng) (tng) 1-3定义的一个切入点的方法就?BankAccountDAO->withdraw(double amount)
(tng) (tng) (tng) 4-6定义的是一个通用的，它的切入Ҏ(gu)所有的com.mc.billing.下面的类的方法?/p>
(tng) (tng) (tng) 既然我们知道?jin)需要用advisor向主要代码中注入“不可见的”adviceQ让我们实现一个Spring AOP的例子。在q个例子中，我们实C个before adviceQ这意味着advice的代码在被调用的publicҎ(gu)开始前被执行。以下是q个before advice的实C码：(x)
(tng) (tng) (tng) 代码:
package com.company.springaop.test;
import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;
public class TestBeforeAdvice implements MethodBeforeAdvice {
public void before(Method m, Object[] args, Object target)
throws Throwable {
(tng) System.out.println("Hello world! (by "
(tng) (tng) (tng) + this.getClass().getName()
(tng) (tng) (tng) + ")");
}
}
(tng) (tng) (tng) 接口MethodBeforeAdvice只有一个方法before需要实玎ͼ它定义了(jin)advice的实现。beforeҎ(gu)q三个参数Q它们提供了(jin)相当丰富的信息。参数Method m是advice开始后执行的方法。方法名U可以用作判断是否执行代码的条g。Object[] args是传l被调用的publicҎ(gu)的参数数l。当需要记日志Ӟ参数args和被执行Ҏ(gu)的名Uͼ都是非常有用的信息。你也可以改变(sh)lm的参敎ͼ但要心(j)使用q个功能Q编写最初主E序的程序员q不知道ȝ序可能会(x)和传入参数的发生冲突。Object target是执行方法m对象的引用?/p>
(tng) (tng) (tng) 在下面的BeanImplcMQ每个publicҎ(gu)调用前，都会(x)执行adviceQ?/p>
(tng) (tng) (tng) 代码:
package com.company.springaop.test;
public class BeanImpl implements Bean {
public void theMethod() {
(tng) System.out.println(this.getClass().getName()
(tng) (tng) (tng) + "." + new Exception().getStackTrace()[0].getMethodName()
(tng) (tng) (tng) + "()"
(tng) (tng) (tng) + " says HELLO!");
}
}
(tng) (tng) (tng) cBeanImpl实现?jin)下面的接口BeanQ?/p>
(tng) (tng) (tng) 代码:
package com.company.springaop.test;
public interface Bean {
public void theMethod();
}
(tng) (tng) (tng) 虽然不是必须使用接口Q但面向接口而不是面向实现编E是良好的编E实践，Spring也鼓p样做?/p>
(tng) (tng) (tng) pointcut和advice通过配置文g来实玎ͼ因此Q接下来你只需~写L法的Java代码Q?/p>
(tng) (tng) (tng) 代码:
package com.company.springaop.test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;
public class Main {
public static void main(String[] args) {
(tng) //Read the configuration file
(tng) ApplicationContext ctx = new FileSystemXmlApplicationContext("springconfig.xml");
(tng) //Instantiate an object
(tng) Bean x = (Bean) ctx.getBean("bean");
(tng) //Execute the public method of the bean (the test)
(tng) x.theMethod();
}
}
(tng) (tng) (tng) 我们从读入和处理配置文g开始，接下来马上要创徏它。这个配|文件将作ؓ(f)_合E序不同部分的“胶水”。读入和处理配置文g后，我们?x)得C个创建工厂ctx。Q何一个Spring理的对象都必须通过q个工厂来创建。对象通过工厂创徏后便可正怋用?/p>
(tng) (tng) (tng) 仅仅用配|文件便可把E序的每一部分l装h?/p>
(tng) (tng) (tng) 代码:
(tng) (tng) (tng) 现在我们需要的是这样一个框Ӟ它可以方便地引入Q且不会(x)对原来的开发和构造过E生Q何媄(jing)响。满些要求的框架不止一个，例如JBoss AOP?span lang="EN-US">Nanning?span lang="EN-US">AspectwerkzQ?span lang="EN-US">AWQ。本文选用的是AspectwerkzQ因为它可能是最Ҏ(gu)学习(fn)的框Ӟ也是最Ҏ(gu)集成到现有项目的框架?font face="?hu)?>
(tng) (tng) (tng) Aspectwerkz?span lang="EN-US">Jonas Boner?span lang="EN-US">Alexandre Vasseur创徏Q它是目前最快速、功能最丰富的框架之一。虽然它q缺?span lang="EN-US">AspectJ的某些功能，但己以满大多数开发者在许多情Ş下的需要?font face="?hu)?>
(tng) (tng) (tng) Aspectwerkz最令h感兴的Ҏ(gu)之一是它能够以两U不同的模式q行Q联机模式和脱机模式。在联机模式下，AW直接q预属于JVM的底层类装入机制Q截取所有的c装入请求，对字节码实施x(chng)转换?span lang="EN-US">AW提供?jin)干预类装入q程的许多选项Q另外还有一个替?span lang="EN-US">bin/java命o(h)的封装脚本，q个脚本能够Ҏ(gu)Java版本?span lang="EN-US">JVM能力自动生成一l可q行的配制。对于开发者，联机模式有许多优点，它能插入CQ何类装入器ƈ在类装入期间生成新的cR也是_(d)我们不必手工修改应用E序的类Q只要按通常的方式部|即可。不q，联机模式要求对应用服务器q行额外的配Ӟ有时q一要求可能很难满?font face="?hu)?>
(tng) (tng) (tng) 在脱机模式下Q生成类需要二个步骤。第一步是用标准的~译器编译，W二步是重点—?/span>以脱机模式运?span lang="EN-US">AWcompiler~译器，让它处理新生成的cR编译器修改这些类的字节码Q根据一?span lang="EN-US">XML文g的定义，在适当?span lang="EN-US">point-cut插入advice。脱机模式的优点?span lang="EN-US">AWcompiler生成的类能够在Q?span lang="EN-US">JVM 1.3以上的虚拟机q行Q本文下面要用的是q种模式Q因为它不需要对Tomcat作Q何修改，只要Ҏ(gu)造过E稍作修改就可以照搬到大多数现有的项目?span lang="EN-US">
(tng) (tng) (tng) 1Q运行时和加载时字节码修正：(x)你可以在q行时或~译时轻杄攚wQ何（旧）(j)应用E序或除?span lang="EN-US">rt.jar以外的外部类?span lang="EN-US">
(tng) (tng) (tng) 2Q支?span lang="EN-US">join point模型
(tng) (tng) (tng) 3Q支?span lang="EN-US">AnnotationQ匹?span lang="EN-US">JavaDoc?span lang="EN-US">JSR-175Q支持用戯定义Annotation
(tng) (tng) (tng) 4Q支持部|多?span lang="EN-US">Aspect定义文g到部|的应用E序Q?span lang="EN-US">WEB-INF/aop.xml?span lang="EN-US">META-INF/aop.xmlQ?span lang="EN-US">
(tng) (tng) (tng) 5Q?span lang="EN-US">Introduction/内类型声明（也称MixinQ，也就是具有添加接口和实现到已存在的类中的能力
(tng) (tng) (tng) 6Q?span lang="EN-US">Annotation定义Q定?span lang="EN-US">Aspect使用的运行时AnnotationQؓ(f)JSR-175准备Q?span lang="EN-US">
(tng) (tng) (tng) 7Q?span lang="EN-US">XML定义Q定?span lang="EN-US">Aspect使用?span lang="EN-US">XMLQ?span lang="EN-US">XML可以用来_、改写和解析Annotation定义
(tng) (tng) (tng) 8Q插件式Aspect理器能够和IoC框架Q如Spring?span lang="EN-US">PicoContainerQ一起工?span lang="EN-US">
(tng) (tng) (tng) 9Q四U不同的Advice?span lang="EN-US">Introduction部v模型Q范_(d)(j)Q?span lang="EN-US">perJVMQ单模式Q?span lang="EN-US"> perClass?span lang="EN-US">perInstance ?span lang="EN-US">perThread
(tng) (tng) (tng) 10Q?span lang="EN-US">Advice?span lang="EN-US">Introduction能够动态部|Ӏ反部v或重新部|?span lang="EN-US">
(tng) (tng) (tng) 11Q高性能Q?span lang="EN-US">JIT~译
(tng) (tng) (tng) 12Q?span lang="EN-US">Fine-grained模式语言选择join point
(tng) (tng) (tng) 13Q所?span lang="EN-US">Advice能够和所有的join point和各U合类型的pointcut
(tng) (tng) (tng) 14Q脱机变换（可以用作后处理器Q?span lang="EN-US">
(tng) (tng) (tng) 15Q?span lang="EN-US">Aspect?span lang="EN-US">Advice?span lang="EN-US">Introduction使用POJO~码
(tng) (tng) (tng) 16Q目标类可以是正规的POJOQ也是不需要接?span lang="EN-US">
(tng) (tng) (tng) 17Q支持通过定义传递参数给Advice和定义可重用?span lang="EN-US">Advice堆栈
(tng) (tng) (tng) 18Q元数据被加到类?span lang="EN-US">
(tng) (tng) (tng) 19Q简单的用法和配|?span lang="EN-US">
开?span lang="EN-US">AOP
1Q这里我们要在屏q打印出?span lang="EN-US">Hello AOP!”，看如下代码：(x)
//HelloAOP.java
public class HelloAOP {
(tng) (tng) (tng) public static void main(String args[]) {
(tng) (tng) (tng) (tng) (tng) (tng) (tng) HelloAOP ha = new HelloAOP();
(tng) (tng) (tng) (tng) (tng) (tng) (tng) ha.test();
(tng) (tng) (tng) }
(tng) (tng) (tng) public void test() {
(tng) (tng) (tng) (tng) (tng) (tng) (tng) System.out.println("Hello AOP!");
(tng) (tng) (tng) }
}
~译HelloAOP.java文gQ?span lang="EN-US">javac HelloAOP.java
2Q现在我要在输出?span lang="EN-US">Hello AOP!”前后做一些工作，q些工作在运行时?x)得到调用机会(x)，如果使?span lang="EN-US">AOP术语Q我们可以说我们要编写我们的aspectQ这?span lang="EN-US">aspect?x)在q行时被weave into Q织入）(j)HelloAOP class?span lang="EN-US">
//MyAspect.java
import org.codehaus.aspectwerkz.joinpoint.JoinPoint;
public class MyAspect {
(tng) (tng) (tng) public void beforeTesting(JoinPoint joinPoint) {
(tng) (tng) (tng) (tng) (tng) (tng) (tng)System.out.println("before testing...");
(tng) (tng) (tng) }
(tng) (tng) (tng) public void afterTesting(JoinPoint joinPoint) {
(tng) (tng) (tng) (tng) (tng) (tng) (tng) System.out.println("after testing...");
(tng) (tng) (tng) }
}
javac MyAspect.java
3Q织入过Eƈ不简单，我们需要撰写一个描q文件来?span lang="EN-US">aspect和其l入?span lang="EN-US">class中的信息联系h?span lang="EN-US">
//aop.xml
<aspectwerkz>
(tng) (tng) (tng) <system id="AspectWerkzExample">
(tng) (tng) (tng) (tng) (tng) (tng) (tng) <aspect class="MyAspect">
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) <pointcut name="testMethod" expression="execution(* HelloAOP.test(..))"/>
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) <advice name="beforeTesting" type="before" bind-to="testMethod"/>
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)<advice name="afterTesting" type="after" bind-to="testMethod"/>
(tng) (tng) (tng) (tng) (tng) (tng) (tng) </aspect>
(tng) (tng) (tng) </system>
</aspectwerkz>
4)run it
aspectwerkz -Daspectwerkz.definition.file=aop.xml HelloAOP
//output:
before testing...
Hello AOP!
after testing...
]]>