Tuesday, August 14, 2012

AOP implementation using annotations


Audience.java:
package com.lnn.advice.auto;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;

@Aspect
public class Audience {

      @Before("execution(* *.perform(..))")
      public void takeSeats() {
            System.out.println("The audience is taking their seats.");
      }

      @Before("execution(* *.perform(..))")
      public void turnOffCellPhones() {
            System.out.println("The audience is turning off their cellphones");
      }

      @AfterReturning("execution(* *.perform(..))")
      public void applaud() {
            System.out.println("CLAP CLAP CLAP CLAP CLAP");
      }

      @AfterThrowing("execution(* *.perform(..))")
      public void demandRefund() {
            System.out.println("Boo! We want our money back!");
      }

      @Around("execution(* *.perform(..))")
      public void watchPerformance(ProceedingJoinPoint joinpoint) {
            try {
                  System.out.println("Before Method");
                  joinpoint.proceed();
                  System.out.println("After Return");
            } catch (Throwable e) {
                  System.out.println("After Throwing.");
            }
      }
}
Instrument.java:
package com.lnn.advice;

public interface Instrument {
      public void play();
}
Violin.java:
package com.lnn.advice;

public class Violin implements Instrument {
      @Override
      public void play() {
            System.out.println("violin is playing now...");
      }
}
PerformanceException:
package com.lnn.advice;

public class PerformanceException extends Exception {

      private static final long serialVersionUID = -6772609716850440380L;
     
}
Performer.java:
package com.lnn.advice;

public interface Performer {
      public void perform() throws PerformanceException;
}
Instrumentalist.java:
package com.lnn.advice;

import com.lnn.advice.Instrument;
import com.lnn.advice.PerformanceException;
import com.lnn.advice.Performer;

public class Instrumentalist implements Performer {
      public Instrumentalist() {
      }

      public void perform() throws PerformanceException {
            System.out.print("Playing " + song + " : ");
            if (instrument != null) {
                  instrument.play();
            } else {
                  throw new PerformanceException();
            }
      }

      private String song;

      public void setSong(String song) {
            this.song = song;
      }

      private Instrument instrument;

      public void setInstrument(Instrument instrument) {
            this.instrument = instrument;
      }
}
auto.xml:
<beans xmlns="http://www.springframework.org/schema/beans"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
      xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">
      <bean id="violin" class="com.lnn.advice.Violin" />
      <bean id="instrumentalist" class="com.lnn.advice.Instrumentalist">
            <property name="song" value="It's My Life" />
            <property name="instrument" ref="violin" />
      </bean>
      <bean id="audience" class="com.lnn.advice.auto.Audience" />
      <aop:aspectj-autoproxy/>        
</beans>
Test.java:
package com.lnn.advice.auto;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.lnn.advice.PerformanceException;
import com.lnn.advice.Performer;

public class Test {
      public static void main(String[] args) throws PerformanceException {
            ApplicationContext context = new ClassPathXmlApplicationContext("aop/auto.xml");
            Performer performer = (Performer) context.getBean("instrumentalist");
            performer.perform();
      }
}

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