org.apache.solr.util.plugin.AbstractPluginLoader Maven / Gradle / Ivy

/**
 * 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.solr.util.plugin;

import java.util.ArrayList;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.solr.common.ResourceLoader;
import org.apache.solr.common.SolrException;
import org.apache.solr.common.util.DOMUtil;
import org.apache.solr.core.SolrConfig;
import org.apache.solr.core.SolrResourceLoader;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * An abstract super class that manages standard solr-style plugin configuration.
 * 
 * @version $Id: AbstractPluginLoader.java 712014 2008-11-06 23:41:39Z yonik $
 * @since solr 1.3
 */
public abstract class AbstractPluginLoader
{
  public static Logger log = LoggerFactory.getLogger(AbstractPluginLoader.class);
  
  private final String type;
  private final boolean preRegister;
  private final boolean requireName;
  
  /**
   * @param type is the 'type' name included in error messages.
   * @param preRegister if true, this will first register all Plugins, then it will initialize them.
   */
  public AbstractPluginLoader( String type, boolean preRegister, boolean requireName )
  {
    this.type = type;
    this.preRegister = preRegister;
    this.requireName = requireName;
  }

  public AbstractPluginLoader( String type )
  {
    this( type, false, true );
  }
  
  /**
   * Where to look for classes
   */
  protected String[] getDefaultPackages()
  {
    return new String[]{};
  }
  
  /**
   * Create a plugin from an XML configuration.  Plugins are defined using:
   *   
   *      ...
   *   
   * 
   * @param name - The registered name.  In the above example: "name1"
   * @param className - class name for requested plugin.  In the above example: "solr.ClassName"
   * @param node - the XML node defining this plugin
   */
  @SuppressWarnings("unchecked")
  protected T create( ResourceLoader loader, String name, String className, Node node ) throws Exception
  {
    return (T) loader.newInstance( className, getDefaultPackages() );
  }
  
  /**
   * Register a plugin with a given name.
   * @return The plugin previously registered to this name, or null
   */
  abstract protected T register( String name, T plugin ) throws Exception;

  /**
   * Initialize the plugin.  
   * 
   * @param plugin - the plugin to initialize
   * @param node - the XML node defining this plugin
   */
  abstract protected void init( T plugin, Node node ) throws Exception;

  /**
   * Given a NodeList from XML in the form:
   * 
   *  
   *    
   *      ...
   *    
   *    
   *      ...
   *    
   *  
   * 
   * This will initialize and register each plugin from the list.  A class will 
   * be generated for each class name and registered to the given name.
   * 
   * If 'preRegister' is true, each plugin will be registered *before* it is initialized
   * This may be useful for implementations that need to inspect other registered 
   * plugins at startup.
   * 
   * One (and only one) plugin may declare itself to be the 'default' plugin using:
   *    
   * If a default element is defined, it will be returned from this function.
   * 
   */
  public T load( ResourceLoader loader, NodeList nodes )
  {
    List info = new ArrayList();
    T defaultPlugin = null;
    
    if (nodes !=null ) {
      for (int i=0; i ... 
   * 
   * This will initialize and register a single plugin. A class will be
   * generated for the plugin and registered to the given name.
   * 
   * If 'preRegister' is true, the plugin will be registered *before* it is
   * initialized This may be useful for implementations that need to inspect
   * other registered plugins at startup.
   * 
   * The created class for the plugin will be returned from this function.
   * 
   */
  public T loadSingle(ResourceLoader loader, Node node) {
    List info = new ArrayList();
    T plugin = null;

    try {
      String name = DOMUtil.getAttr(node, "name", requireName ? type : null);
      String className = DOMUtil.getAttr(node, "class", type);
      plugin = create(loader, name, className, node);
      log.info("created " + name + ": " + plugin.getClass().getName());

      // Either initialize now or wait till everything has been registered
      if (preRegister) {
        info.add(new PluginInitInfo(plugin, node));
      } else {
        init(plugin, node);
      }

      T old = register(name, plugin);
      if (old != null && !(name == null && !requireName)) {
        throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
            "Multiple " + type + " registered to the same name: " + name
                + " ignoring: " + old);
      }

    } catch (Exception e) {
      SolrConfig.severeErrors.add(e);
      SolrException.logOnce(log, null, e);
    }

    // If everything needs to be registered *first*, this will initialize later
    for (PluginInitInfo pinfo : info) {
      try {
        init(pinfo.plugin, pinfo.node);
      } catch (Exception ex) {
        SolrConfig.severeErrors.add(ex);
        SolrException.logOnce(log, null, ex);
      }
    }
    return plugin;
  }
  

  /**
   * Internal class to hold onto initialization info so that it can be initialized 
   * after it is registered.
   */
  private class PluginInitInfo
  {
    final T plugin;
    final Node node;
    
    PluginInitInfo( T plugin, Node node )
    {
      this.plugin = plugin;
      this.node = node;
    }
  }
}