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翻译-面向方面编程和JBoss之二

摘要: 翻译-面向方面编程和JBoss之二

public class TracingInterceptor implements Interceptor
{
 public String getName() { return TracingInterceptor; }
 public InvocationResponse invoke(Invocation invocation) 
  throws Throwable
 {
  String filter = (String)invocation.getMetaData(tracing, filter);
  if (filter != null && filter.equals(true))
     return invocation.invokeNext();

  String message = null;

  if (invocation.getType() == InvocationType.METHOD)
  {
   Method method = MethodInvocation.getMethod(invocation);
   message  = method: + method.getName();
  }
  else if (invocation.getType() == InvocationType.CONSTRUCTOR)
  {
   Constructor c = ConstructorInvocation.getConstructor(invocation);
   message  = constructor: + c.toString();
  }
  else
  {
   // Do nothing for fields. Just too verbose.
   return invocation.invokeNext();
  }

  System.out.println(Entering + message);

  // Continue on. Invoke the real method or constructor.
  InvocationResponse rsp = invocation.invokeNext();
  System.out.println(Leaving + message);
  return rsp;
 }
}

POJO类将扩展一点，增加get()和set()方法。
public class POJO
{
 public POJO() {}
 public void helloWorld() { System.out.println(Hello World!); }

 private int counter = 0;

 public int getCounter() { return counter; }
 public void setCounter(int val) { counter = val; }
 public static void main(String[] args)
 {
  POJO pojo = new POJO();
  pojo.helloWorld();
  pojo.setCounter(32);
  System.out.println(counter is: + pojo.getCounter());
 }
}
TracingInterceptor将拦截对main()，POJO()和helloWorld()调用。输出应该看起来如下：
Entering constructor: public POJO()
Leaving constructor: public POJO()
Entering method: helloWorld
Hello World!
Leaving method: helloWorld

public interface Tracing
{
 public void enableTracing();
 public void disableTracing();
}

import org.jboss.aop.Advised;

public class TracingMixin implements Tracing
{
 Advised advised;

 Public TracingMixin(Object obj)
 {
  this.advised = (Advised)obj;
 }

 public void enableTracing()
 {
  advised._getInstanceAdvisor().getMetaData().addMetaData(
     "tracing", "filter", true);
 }

 public void disableTracing()
 {
  advised._getInstanceAdvisor().getMetaData().addMetaData(
     "tracing", "filter", false);
 }
}

<?xml version="1.0" encoding="UTF-8">

 
  
   Tracing
   TracingMixin
   new TracingMixin(this)
  
 

public class POJO
{
 public POJO() {}
 public void helloWorld() { System.out.println(Hello World!); }

 public static void main(String[] args)
 {
  POJO pojo  = new POJO();
  Tracing trace = (Tracing)this;
  pojo.helloWorld();

  System.out.println("Turn off tracing.");

  trace.disableTracing();
  pojo.helloWorld();

  System.out.println("Turn on tracing.");

  trace.enableTracing();
  pojo.helloWorld();
 }
}

Entering constructor: POJO()
Leaving constructor: POJO()
Entering method: helloWorld
Hello World!
Leaving method: helloWorld
Turn off tracing.
Entering method: disableTracing
Leaving method: disableTracing
Hello World!
Turn on tracing.
Entering method: helloWorld
Hello World!
Leaving method: helloWorld

$ cd oreilly-aop/example3
$ export CLASSPATH=.;jboss-common.jar;jboss-aop.jar;javassist.jar
$ javac *.java
$ java -Djava.system.class.loader=org.jboss.aop.standalone.SystemClassLoader POJO