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Plugin Framework
There is a newer version: 1.10
/**
 * Copyright (C) 2008 Mathieu Carbou 
 *
 * Licensed 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 com.mycila.plugin.spi;

import com.mycila.log.Logger;
import com.mycila.log.Loggers;
import com.mycila.plugin.api.Plugin;
import com.mycila.plugin.api.PluginBinding;
import com.mycila.plugin.api.PluginCache;
import com.mycila.plugin.api.PluginLoader;
import static com.mycila.plugin.spi.Ensure.*;

import java.util.Arrays;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @author Mathieu Carbou ([email protected])
 */
final class DefaultPluginCache implements PluginCache {

    private static final Logger LOGGER = Loggers.get(DefaultPluginCache.class);

    final ConcurrentHashMap> plugins = new ConcurrentHashMap>();
    final PluginLoader loader;
    volatile boolean loaded;

    DefaultPluginCache(PluginLoader loader) {
        notNull("Plugin loader", loader);
        this.loader = loader;
    }

    public void clear() {
        plugins.clear();
        loaded = false;
    }

    public void registerPlugin(String name, T plugin) {
        notEmpty("Plugin name", name);
        notNull("Plugin instance", plugin);
        LOGGER.debug("Adding plugin: {0}", name);
        plugins.put(name, new Binding(name).withPlugin(plugin));
    }

    public void registerPlugins(Map plugins) {
        notNull("Plugin map", plugins);
        for (Map.Entry entry : plugins.entrySet()) {
            registerPlugin(entry.getKey(), entry.getValue());
        }
    }

    public void removePlugins(String... pluginNames) {
        notNull("Plugin names", pluginNames);
        LOGGER.debug("Removing plugins: {0}", Arrays.toString(pluginNames));
        for (String name : pluginNames) {
            this.plugins.remove(name);
        }
    }

    public boolean contains(String pluginName) {
        notNull("Plugin name", pluginName);
        return bindings().containsKey(pluginName);
    }

    public Map> getBindings() {
        return Collections.unmodifiableMap(bindings());
    }

    private Map> bindings() {
        if (!loaded) {
            synchronized (this) {
                if (!loaded) {
                    for (PluginBinding binding : loader.loadPlugins()) {
                        plugins.put(binding.getName(), binding);
                    }
                    loaded = true;
                }
            }
        }
        return plugins;
    }
}