CdiContainerLoader.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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 org.apache.deltaspike.cdise.api;

import java.util.Iterator;
import java.util.ServiceLoader;

/**
 * <p>This class provides access to the ContainerControl.</p>
 * <p>It uses the {@code java.util.ServiceLoader} mechanism  to 
 * automatically pickup the container providers from the classpath.</p>
 * <p>Usage:
 * <pre>
 *     CdiContainer container = CdiContainerLoader.getCdiContainer();
 *     container.boot();
 *     ...
 * </pre>
 * </p>
 * <p>CdiContainerLoader internally uses the {@link java.util.ServiceLoader}
 * to automatically detect the container implementation which should be used.
 * </p>
 */
public final class CdiContainerLoader
{
    private static CdiContainer cdiContainer = null;

    private CdiContainerLoader()
    {
        // private ct to prevent instantiation
    }


    /**
     * @return the {@link CdiContainer} implementation available on the classpath
     * @throws IllegalStateException if none or multiple CdiContainer implementations
     *         are found on the classpath.
     */
    public static synchronized CdiContainer getCdiContainer()
    {
        if (cdiContainer == null)
        {
            // there is no dependency to any cdi implementation, we do all dynamically
            ServiceLoader<CdiContainer> cdiContainerLoader = ServiceLoader.load(CdiContainer.class);
            Iterator<CdiContainer> cdiIt = cdiContainerLoader.iterator();
            if (cdiIt.hasNext())
            {
                cdiContainer = cdiIt.next();
            }
            else
            {
                throw new IllegalStateException("Could not find an implementation of " + CdiContainer.class.getName() +
                    " available in the classpath!");
            }

            if (cdiIt.hasNext())
            {
                String foundContainers = getContainerDetails();
                throw new IllegalStateException("Too many implementations of " + CdiContainer.class.getName() +
                    " found in the classpath! Details: " + foundContainers);
            }
        }
        return cdiContainer;
    }

    private static String getContainerDetails()
    {
        StringBuilder result = new StringBuilder();

        Class containerClass;
        for (CdiContainer cdiContainer : ServiceLoader.load(CdiContainer.class))
        {
            containerClass = cdiContainer.getClass();
            result.append(containerClass.getProtectionDomain().getCodeSource().getLocation().toExternalForm());
            result.append(containerClass.getName());

            result.append(System.getProperty("line.separator"));
        }

        return result.toString();
    }
}