org.apache.hama.monitor.Configurator.java Source code

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Here is the source code for org.apache.hama.monitor.Configurator.java

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/**
 * 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.hama.monitor;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hama.HamaConfiguration;
import org.apache.hama.monitor.Monitor.Task;

/**
 * Configurator loads and configure jar files.
 */
public final class Configurator {

    public static final Log LOG = LogFactory.getLog(Configurator.class);
    public static final String DEFAULT_PLUGINS_DIR = "plugins";
    private static final ConcurrentMap<String, Long> repos = new ConcurrentHashMap<String, Long>();

    /**
     * Configure plugins directory for monitoring GroomServer.
     * 
     * @param conf file points out the plugin dir location.
     * @return Map contains jar path and task to be executed; null if plugin
     *         directory, default set to $HAMA_HOME/plugins, doesn't exist.
     */
    public static Map<String, Task> configure(HamaConfiguration conf, MonitorListener listener) throws IOException {
        String hamaHome = System.getProperty("hama.home.dir");
        String pluginPath = conf.get("bsp.monitor.plugins.dir", hamaHome + File.separator + DEFAULT_PLUGINS_DIR);
        File pluginDir = new File(pluginPath);
        if (null == pluginDir || null == pluginDir.listFiles())
            return null;
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Map<String, Task> taskList = new HashMap<String, Task>();
        LOG.debug("Scanning jar files within " + pluginDir + ".");
        for (File jar : pluginDir.listFiles()) {
            String jarPath = jar.getPath();
            Long timestamp = repos.get(jarPath);
            if (null == timestamp || jar.lastModified() > timestamp) {
                Task t = load(jar, loader);
                if (null != t) {
                    t.setListener(listener);
                    taskList.put(jarPath, t);
                    repos.put(jarPath, jar.lastModified());
                    LOG.debug(jar.getName() + " is loaded.");
                }
            }
        }
        return taskList;
    }

    /**
     * Load jar from specified path.
     * 
     * @param path to the jar file.
     * @param loader of the current thread.
     * @return task to be run.
     */
    private static Task load(File path, ClassLoader loader) throws IOException {
        JarFile jar = new JarFile(path);
        Manifest manifest = jar.getManifest();
        String pkg = manifest.getMainAttributes().getValue("Package");
        String main = manifest.getMainAttributes().getValue("Main-Class");
        if (null == pkg || null == main)
            throw new NullPointerException("Package or main class not found " + "in menifest file.");
        String namespace = pkg + File.separator + main;
        namespace = namespace.replaceAll(File.separator, ".");
        LOG.debug("Task class to be loaded: " + namespace);
        URLClassLoader child = new URLClassLoader(new URL[] { path.toURI().toURL() }, loader);
        Thread.currentThread().setContextClassLoader(child);
        Class<?> taskClass = null;
        try {
            taskClass = Class.forName(namespace, true, child); // task class
        } catch (ClassNotFoundException cnfe) {
            LOG.warn("Task class is not found.", cnfe);
        }
        if (null == taskClass)
            return null;

        try {
            return (Task) taskClass.newInstance();
        } catch (InstantiationException ie) {
            LOG.warn("Unable to instantiate task class." + namespace, ie);
        } catch (IllegalAccessException iae) {
            LOG.warn(iae);
        }
        return null;
    }

}