camel-core/src/main/java/org/apache/camel/impl/DefaultComponentResolver.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.camel.impl;

import java.io.IOException;

import org.apache.camel.CamelContext;
import org.apache.camel.Component;
import org.apache.camel.NoFactoryAvailableException;
import org.apache.camel.spi.ComponentResolver;
import org.apache.camel.spi.FactoryFinder;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * The default implementation of {@link ComponentResolver} which tries to find
 * components by using the URI scheme prefix and searching for a file of the URI
 * scheme name in the <b>META-INF/services/org/apache/camel/component/</b>
 * directory on the classpath.
 *
 * @version $Revision$
 */
public class DefaultComponentResolver implements ComponentResolver {

    public static final String RESOURCE_PATH = "META-INF/services/org/apache/camel/component/";
    private static final transient Log LOG = LogFactory.getLog(DefaultComponentResolver.class);
    private FactoryFinder factoryFinder;

    @SuppressWarnings("unchecked")
    public Component resolveComponent(String name, CamelContext context) {
        // lookup in registry first
        Object bean = null;
        try {
            bean = context.getRegistry().lookup(name);
            if (bean != null && getLog().isDebugEnabled()) {
                getLog().debug("Found component: " + name + " in registry: " + bean);
            }
        } catch (Exception e) {
            getLog().debug("Ignored error looking up bean: " + name, e);
        }
        if (bean != null) {
            if (bean instanceof Component) {
                return (Component) bean;
            }
            // we do not throw the exception here and try to auto create a component
        }

        // not in registry then use component factory
        Class type;
        try {
            type = findComponent(name, context);
            if (type == null) {
                // not found
                return null;
            }
        } catch (NoFactoryAvailableException e) {
            return null;
        } catch (Exception e) {
            throw new IllegalArgumentException("Invalid URI, no Component registered for scheme: " + name, e);
        }

        if (getLog().isDebugEnabled()) {
            getLog().debug("Found component: " + name + " via type: " + type.getName() + " via: " + factoryFinder.getResourcePath() + name);
        }

        // create the component
        if (Component.class.isAssignableFrom(type)) {
            return (Component) context.getInjector().newInstance(type);
        } else {
            throw new IllegalArgumentException("Type is not a Component implementation. Found: " + type.getName());
        }
    }

    private Class<?> findComponent(String name, CamelContext context) throws ClassNotFoundException, IOException {
        if (factoryFinder == null) {
            factoryFinder = context.getFactoryFinder(RESOURCE_PATH);
        }
        return factoryFinder.findClass(name);
    }

    protected Log getLog() {
        return LOG;
    }

}