001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.camel.impl;
018    
019    import java.io.IOException;
020    
021    import org.apache.camel.CamelContext;
022    import org.apache.camel.Component;
023    import org.apache.camel.NoFactoryAvailableException;
024    import org.apache.camel.spi.ComponentResolver;
025    import org.apache.camel.spi.FactoryFinder;
026    import org.apache.commons.logging.Log;
027    import org.apache.commons.logging.LogFactory;
028    
029    /**
030     * The default implementation of {@link ComponentResolver} which tries to find
031     * components by using the URI scheme prefix and searching for a file of the URI
032     * scheme name in the <b>META-INF/services/org/apache/camel/component/</b>
033     * directory on the classpath.
034     *
035     * @version $Revision: 754461 $
036     */
037    public class DefaultComponentResolver implements ComponentResolver {
038    
039        public static final String RESOURCE_PATH = "META-INF/services/org/apache/camel/component/";
040        private static final transient Log LOG = LogFactory.getLog(DefaultComponentResolver.class);
041        private FactoryFinder factoryFinder;
042    
043        @SuppressWarnings("unchecked")
044        public Component resolveComponent(String name, CamelContext context) {
045            // lookup in registry first
046            Object bean = null;
047            try {
048                bean = context.getRegistry().lookup(name);
049                if (bean != null && getLog().isDebugEnabled()) {
050                    getLog().debug("Found component: " + name + " in registry: " + bean);
051                }
052            } catch (Exception e) {
053                getLog().debug("Ignored error looking up bean: " + name, e);
054            }
055            if (bean != null) {
056                if (bean instanceof Component) {
057                    return (Component) bean;
058                }
059                // we do not throw the exception here and try to auto create a component
060            }
061    
062            // not in registry then use component factory
063            Class type;
064            try {
065                type = findComponent(name, context);
066                if (type == null) {
067                    // not found
068                    return null;
069                }
070            } catch (NoFactoryAvailableException e) {
071                return null;
072            } catch (Exception e) {
073                throw new IllegalArgumentException("Invalid URI, no Component registered for scheme: " + name, e);
074            }
075    
076            if (getLog().isDebugEnabled()) {
077                getLog().debug("Found component: " + name + " via type: " + type.getName() + " via: " + factoryFinder.getResourcePath() + name);
078            }
079    
080            // create the component
081            if (Component.class.isAssignableFrom(type)) {
082                return (Component) context.getInjector().newInstance(type);
083            } else {
084                throw new IllegalArgumentException("Type is not a Component implementation. Found: " + type.getName());
085            }
086        }
087    
088        private Class findComponent(String name, CamelContext context) throws ClassNotFoundException, IOException {
089            if (factoryFinder == null) {
090                factoryFinder = context.getFactoryFinder(RESOURCE_PATH);
091            }
092            return factoryFinder.findClass(name);
093        }
094    
095        protected Log getLog() {
096            return LOG;
097        }
098    
099    }