Implementation of CAS using AspectJ

readme.md

Follow these steps to use the CAS annotation feature.

1. Add the @EnableCAS annotation to inject CAS behavior into a class.

2. Add the following to the VM arguments of your application:

   -javaagent:/home/user/.m2/repository/org/aspectj/aspectjweaver/1.8.6/aspectjweaver-1.8.6.jar

CheckAndSet.java

/*
 * Copyright 2015 Piazza Software Consulting, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.piazzaconsulting.couchbase.cas;

/**
 * Simple interface to describe behavior needed to support CAS.
 * 
 * @author Tony Piazza
 */
public interface CheckAndSet {
	long getCas();
	void setCas(long cas);
}

CheckAndSetAspect.java

/*
 * Copyright 2015 Piazza Software Consulting, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.piazzaconsulting.couchbase.cas;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.DeclareParents;

/**
 * Aspect for injecting CAS behavior into classes that will be stored in 
 * Couchbase.
 * 
 * @author Tony Piazza
 */
@Aspect
public class CheckAndSetAspect {
	public static class CheckAndSetSupportImpl implements CheckAndSet {
		private long cas;

		@Override
		public long getCas() {
			return cas;
		}

		@Override
		public void setCas(long cas) {
			this.cas = cas;
		}
	}

	@DeclareParents(value="@EnableCAS *",defaultImpl=CheckAndSetSupportImpl.class)
	private CheckAndSet implementedInterface;
}

CheckAndSetUtil.java

/*
 * Copyright 2015 Piazza Software Consulting, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.piazzaconsulting.couchbase.cas;

/**
 * Utility class for using the CAS capability injected by the EnableCAS
 * annotation.
 * 
 * @author Tony Piazza
 */
public final class CheckAndSetUtil {
	private CheckAndSetUtil() {
		// prevents instantiation
	}

	/**
	 * Set the CAS value of the target object.
	 * 
	 * @param target Object reference of target
	 * @param cas long CAS value
	 */
	public static void set(Object target, long cas) {
		getObject(target).setCas(cas);
	}

	/**
	 * Get the CAS value of the target object.
	 * 
	 * @param target Object reference of target
	 * @return long CAS value
	 */
	public static long get(Object obj) {
		return getObject(obj).getCas();
	}

	private static CheckAndSet getObject(Object obj) {
		if(!(obj instanceof CheckAndSet)) {
			throw new IllegalArgumentException("Type does not implement " + 
				CheckAndSet.class.getName());
		}
		return (CheckAndSet)obj;
	}
}

EnableCAS.java

/*
 * Copyright 2015 Piazza Software Consulting, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.piazzaconsulting.couchbase.cas;

import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Marker annotation to identify classes that want CAS behavior injected.
 * 
 * @author Tony Piazza
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Inherited
public @interface EnableCAS {
	// nothing needed here
}