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/* 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 org.activiti.engine;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.activiti.engine.impl.ProcessEngineInfoImpl;
import org.activiti.engine.impl.util.IoUtil;
import org.activiti.engine.impl.util.ReflectUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Helper for initializing and closing process engines in server environments. 

 * All created {@link ProcessEngine}s will be registered with this class. 

 * The activiti-webapp-init webapp will call the {@link #init()} method when the webapp is deployed and it will call the {@link #destroy()} method when the webapp is destroyed, using a
 * context-listener ( org.activiti.impl.servlet.listener.ProcessEnginesServletContextListener ). That way, all applications can just use the {@link #getProcessEngines()} to obtain
 * pre-initialized and cached process engines. 

 * 

 * Please note that there is no lazy initialization of process engines, so make sure the context-listener is configured or {@link ProcessEngine}s are already created so they were registered on
 * this class.

 * 

 * The {@link #init()} method will try to build one {@link ProcessEngine} for each activiti.cfg.xml file found on the classpath. If you have more then one, make sure you specify different
 * process.engine.name values.
 * 


 */
public abstract class ProcessEngines {

  private static Logger log = LoggerFactory.getLogger(ProcessEngines.class);

  public static final String NAME_DEFAULT = "default";

  protected static boolean isInitialized;
  protected static Map processEngines = new HashMap();
  protected static Map processEngineInfosByName = new HashMap();
  protected static Map processEngineInfosByResourceUrl = new HashMap();
  protected static List processEngineInfos = new ArrayList();

  /**
   * Initializes all process engines that can be found on the classpath for resources activiti.cfg.xml (plain Activiti style configuration) and for resources
   * activiti-context.xml (Spring style configuration).
   */
  public synchronized static void init() {
    if (!isInitialized()) {
      if (processEngines == null) {
        // Create new map to store process-engines if current map is
        // null
        processEngines = new HashMap();
      }
      ClassLoader classLoader = ReflectUtil.getClassLoader();
      Enumeration resources = null;
      try {
        resources = classLoader.getResources("activiti.cfg.xml");
      } catch (IOException e) {
        throw new ActivitiIllegalArgumentException("problem retrieving activiti.cfg.xml resources on the classpath: " + System.getProperty("java.class.path"), e);
      }

      // Remove duplicated configuration URL's using set. Some
      // classloaders may return identical URL's twice, causing duplicate
      // startups
      Set configUrls = new HashSet();
      while (resources.hasMoreElements()) {
        configUrls.add(resources.nextElement());
      }
      for (Iterator iterator = configUrls.iterator(); iterator.hasNext();) {
        URL resource = iterator.next();
        log.info("Initializing process engine using configuration '{}'", resource.toString());
        initProcessEngineFromResource(resource);
      }

      try {
        resources = classLoader.getResources("activiti-context.xml");
      } catch (IOException e) {
        throw new ActivitiIllegalArgumentException("problem retrieving activiti-context.xml resources on the classpath: " + System.getProperty("java.class.path"), e);
      }
      while (resources.hasMoreElements()) {
        URL resource = resources.nextElement();
        log.info("Initializing process engine using Spring configuration '{}'", resource.toString());
        initProcessEngineFromSpringResource(resource);
      }

      setInitialized(true);
    } else {
      log.info("Process engines already initialized");
    }
  }

  protected static void initProcessEngineFromSpringResource(URL resource) {
    try {
      Class springConfigurationHelperClass = ReflectUtil.loadClass("org.activiti.spring.SpringConfigurationHelper");
      Method method = springConfigurationHelperClass.getDeclaredMethod("buildProcessEngine", new Class[] { URL.class });
      ProcessEngine processEngine = (ProcessEngine) method.invoke(null, new Object[] { resource });

      String processEngineName = processEngine.getName();
      ProcessEngineInfo processEngineInfo = new ProcessEngineInfoImpl(processEngineName, resource.toString(), null);
      processEngineInfosByName.put(processEngineName, processEngineInfo);
      processEngineInfosByResourceUrl.put(resource.toString(), processEngineInfo);

    } catch (Exception e) {
      throw new ActivitiException("couldn't initialize process engine from spring configuration resource " + resource.toString() + ": " + e.getMessage(), e);
    }
  }

  /**
   * Registers the given process engine. No {@link ProcessEngineInfo} will be available for this process engine. An engine that is registered will be closed when the {@link ProcessEngines#destroy()}
   * is called.
   */
  public static void registerProcessEngine(ProcessEngine processEngine) {
    processEngines.put(processEngine.getName(), processEngine);
  }

  /**
   * Unregisters the given process engine.
   */
  public static void unregister(ProcessEngine processEngine) {
    processEngines.remove(processEngine.getName());
  }

  private static ProcessEngineInfo initProcessEngineFromResource(URL resourceUrl) {
    ProcessEngineInfo processEngineInfo = processEngineInfosByResourceUrl.get(resourceUrl.toString());
    // if there is an existing process engine info
    if (processEngineInfo != null) {
      // remove that process engine from the member fields
      processEngineInfos.remove(processEngineInfo);
      if (processEngineInfo.getException() == null) {
        String processEngineName = processEngineInfo.getName();
        processEngines.remove(processEngineName);
        processEngineInfosByName.remove(processEngineName);
      }
      processEngineInfosByResourceUrl.remove(processEngineInfo.getResourceUrl());
    }

    String resourceUrlString = resourceUrl.toString();
    try {
      log.info("initializing process engine for resource {}", resourceUrl);
      ProcessEngine processEngine = buildProcessEngine(resourceUrl);
      String processEngineName = processEngine.getName();
      log.info("initialised process engine {}", processEngineName);
      processEngineInfo = new ProcessEngineInfoImpl(processEngineName, resourceUrlString, null);
      processEngines.put(processEngineName, processEngine);
      processEngineInfosByName.put(processEngineName, processEngineInfo);
    } catch (Throwable e) {
      log.error("Exception while initializing process engine: {}", e.getMessage(), e);
      processEngineInfo = new ProcessEngineInfoImpl(null, resourceUrlString, getExceptionString(e));
    }
    processEngineInfosByResourceUrl.put(resourceUrlString, processEngineInfo);
    processEngineInfos.add(processEngineInfo);
    return processEngineInfo;
  }

  private static String getExceptionString(Throwable e) {
    StringWriter sw = new StringWriter();
    PrintWriter pw = new PrintWriter(sw);
    e.printStackTrace(pw);
    return sw.toString();
  }

  private static ProcessEngine buildProcessEngine(URL resource) {
    InputStream inputStream = null;
    try {
      inputStream = resource.openStream();
      ProcessEngineConfiguration processEngineConfiguration = ProcessEngineConfiguration.createProcessEngineConfigurationFromInputStream(inputStream);
      return processEngineConfiguration.buildProcessEngine();

    } catch (IOException e) {
      throw new ActivitiIllegalArgumentException("couldn't open resource stream: " + e.getMessage(), e);
    } finally {
      IoUtil.closeSilently(inputStream);
    }
  }

  /** Get initialization results. */
  public static List getProcessEngineInfos() {
    return processEngineInfos;
  }

  /**
   * Get initialization results. Only info will we available for process engines which were added in the {@link ProcessEngines#init()}. No {@link ProcessEngineInfo} is available for engines which were
   * registered programatically.
   */
  public static ProcessEngineInfo getProcessEngineInfo(String processEngineName) {
    return processEngineInfosByName.get(processEngineName);
  }

  public static ProcessEngine getDefaultProcessEngine() {
    return getProcessEngine(NAME_DEFAULT);
  }

  /**
   * obtain a process engine by name.
   * 
   * @param processEngineName
   *          is the name of the process engine or null for the default process engine.
   */
  public static ProcessEngine getProcessEngine(String processEngineName) {
    if (!isInitialized()) {
      init();
    }
    return processEngines.get(processEngineName);
  }

  /**
   * retries to initialize a process engine that previously failed.
   */
  public static ProcessEngineInfo retry(String resourceUrl) {
    log.debug("retying initializing of resource {}", resourceUrl);
    try {
      return initProcessEngineFromResource(new URL(resourceUrl));
    } catch (MalformedURLException e) {
      throw new ActivitiIllegalArgumentException("invalid url: " + resourceUrl, e);
    }
  }

  /**
   * provides access to process engine to application clients in a managed server environment.
   */
  public static Map getProcessEngines() {
    return processEngines;
  }

  /**
   * closes all process engines. This method should be called when the server shuts down.
   */
  public synchronized static void destroy() {
    if (isInitialized()) {
      Map engines = new HashMap(processEngines);
      processEngines = new HashMap();

      for (String processEngineName : engines.keySet()) {
        ProcessEngine processEngine = engines.get(processEngineName);
        try {
          processEngine.close();
        } catch (Exception e) {
          log.error("exception while closing {}", (processEngineName == null ? "the default process engine" : "process engine " + processEngineName), e);
        }
      }

      processEngineInfosByName.clear();
      processEngineInfosByResourceUrl.clear();
      processEngineInfos.clear();

      setInitialized(false);
    }
  }

  public static boolean isInitialized() {
    return isInitialized;
  }

  public static void setInitialized(boolean isInitialized) {
    ProcessEngines.isInitialized = isInitialized;
  }
}