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The Drools and jBPM internal API which is NOT backwards compatible between releases.

There is a newer version: 10.0.0

/*
 * Copyright 2015 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * 
 *      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 org.kie.internal.runtime.cdi;

import javax.enterprise.event.Observes;
import javax.enterprise.inject.spi.AnnotatedType;
import javax.enterprise.inject.spi.BeanManager;
import javax.enterprise.inject.spi.Extension;
import javax.enterprise.inject.spi.ProcessAnnotatedType;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ActivateExtension implements Extension {
	
	private static final Logger logger = LoggerFactory.getLogger(ActivateExtension.class);
	
     void processAnnotatedType(@Observes final ProcessAnnotatedType pat, BeanManager beanManager) {
        final AnnotatedType annotatedType = pat.getAnnotatedType();
        final Class javaClass = annotatedType.getJavaClass();
        
        if (javaClass.isAnnotationPresent(Activate.class)) {
        	
        	Activate veto = javaClass.getAnnotation(Activate.class);
        	String whenAvailable = veto.whenAvailable();
        	String whenNotAvailable = veto.whenNotAvailable();        
        	
        	if (isNotEmpty(whenAvailable) && !isAvailable(whenAvailable, true)) {
        		// veto bean in case whenAvailable is not present
        		pat.veto();
        	}
        	
        	if (isNotEmpty(whenNotAvailable) && isAvailable(whenNotAvailable, false)) {
        		// veto bean in case whenNotAvailable is present
        		pat.veto();
        	}
        }
        return;
    }

    protected boolean isAvailable(String classname, boolean expected) {
		ClassLoader cl = this.getClass().getClassLoader();
		
		boolean result = isAvailable(classname, cl);
		if (result != expected) {
			result = isAvailable(classname, Thread.currentThread().getContextClassLoader());
		}
			
		return result;
	}
	
	protected boolean isAvailable(String classname, ClassLoader classloader) {
		logger.debug("Checking if class {} exists in classloader {}", classname, classloader);
		try {
			Class.forName(classname, true, classloader);
			logger.debug("Class {} exists", classname);
			return true;
		} catch (ClassNotFoundException e) {
			logger.debug("Class {} does NOT exists", classname);
			return false;
		}
	}
	
	protected boolean isNotEmpty(String value) {
		if (value != null && !value.isEmpty()) {
			return true;
		}
		
		return false;
	}
}