Tuesday, August 14, 2012

AOP Implementation using MethodBeforeAdvice


Audience.java:
package com.lnn.advice;

public class Audience {
      public Audience() {
      }

      public void takeSeats() {
            System.out.println("The audience is taking their seats.");
      }

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

      public void applaud() {
            System.out.println("CLAP CLAP CLAP CLAP CLAP");
      }

      public void demandRefund() {
            System.out.println("Boo! We want our money back!");
      }
}
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;
      }
}
BeforeAdvice.java:
package com.lnn.advice.before;

import java.lang.reflect.Method;

import org.springframework.aop.MethodBeforeAdvice;

import com.lnn.advice.Audience;

public class BeforeAdvice implements MethodBeforeAdvice {
      private Audience audience;

      public void setAudience(Audience audience) {
            this.audience = audience;
      }

      @Override
      public void before(Method arg0, Object[] arg1, Object arg2) throws Throwable {
            audience.takeSeats();
            audience.turnOffCellPhones();
      }
}
before.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="instrumentalist" class="com.lnn.advice.Instrumentalist">
            <property name="song" value="It's My Life" />
            <property name="instrument" ref="violin" />
      </bean>
      <bean id="violin" class="com.lnn.advice.Violin" />
      <bean id="audience" class="com.lnn.advice.Audience" />
      <bean id="audienceAdvice" class="com.lnn.advice.before.BeforeAdvice">
            <property name="audience" ref="audience" />
      </bean>
      <bean id="performancePointcut" class="org.springframework.aop.support.JdkRegexpMethodPointcut">
            <property name="pattern" value=".*perform" />
      </bean>
      <bean id="audienceAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">
            <property name="advice" ref="audienceAdvice" />
            <property name="pointcut" ref="performancePointcut" />
      </bean>
      <bean id="instrumentalistproxy" class="org.springframework.aop.framework.ProxyFactoryBean">
            <property name="target" ref="instrumentalist" />
            <property name="interceptorNames" value="audienceAdvisor" />
            <property name="proxyInterfaces" value="com.lnn.advice.Performer" />
      </bean>
</beans>
Test.java:
package com.lnn.advice.before;

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/before.xml");
            Performer performer = (Performer) context.getBean("instrumentalistproxy");
            performer.perform();
      }
}

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