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Snowflake Common Package
There is a newer version: 5.1.4
/*
 * Copyright (c) 2012, 2013 Snowflake Computing Inc. All right reserved.
 */
package net.snowflake.common.core;

import java.text.MessageFormat;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import java.util.Set;

/**
 * Handle error messages.
 *
 * This class encapsulate error message localization using Java bundle.
 *
 * @author tcruanes
 */
public class ResourceBundleManager
{
  private static Map resourceManagers =
      new HashMap();

  private final static Object lockObject = new Object();

  // The name of the Snowflake message file
  private final String bundleName;
  private ResourceBundle resourceBundle;

  private ResourceBundleManager(String bundleName)
  {
    this.bundleName = bundleName;

    // just call reload to load the resournce bundle initially
    reload();
  }

  /**
   * Reload the error message bundle based on the current locale.
   *
   */
  public void reload()
  {
    ResourceBundle bundle = null;

    // Try to load the localized bundle, if it was not found or an error was
    // raised, try to load the default (english) version of the bundle that
    // should always be there.
    try
    {
      // try to get localized version
      bundle = ResourceBundle.getBundle(bundleName,
                                        Locale.getDefault());
    }
    catch (Throwable ex1)
    {
      try
      {
        // Try to load the general bundle (without locale, US)
        bundle = ResourceBundle.getBundle(bundleName);
      }
      catch (Throwable ex2)
      {
        throw new RuntimeException ("Can't load localized resource bundle due to " +
                                    ex1.toString() +
                                    " and can't load default resource bundle due to " +
                                    ex2.toString());
      }
    }
    finally
    {
      resourceBundle = bundle;
    }
  }

  /**
   * Returns the localized error message for the given message key
   *
   * @param key
   *   the message key
   *
   * @return The localized message for the key
   */
  public String getLocalizedMessage(String key)
  {
    // Make sure that the message resource bundle was loaded.
    if (resourceBundle == null)
    {
      throw new RuntimeException("Localized messages from resource bundle '" +
                                 bundleName + "' not loaded.");
    }

    // Try to find the corresponding key
    try
    {
      if (key == null)
      {
        throw new IllegalArgumentException("Message key cannot be null");
      }

      String message = resourceBundle.getString(key);

      // Message not found in the bundle,
      if (message == null)
      {
        message = "!!" + key + "!!";
      }

      return message;
    }
    catch (MissingResourceException e)
    {
      return '!' + key + '!';
    }
  }

  /**
   * Returns the localized error message for the given message key and use
   * the arguments to returned a formatted result string.
   *
   * @param key message key
   * @param args arguments of message
   * @return a localized message
   */
  public String getLocalizedMessage(String key, Object... args)
  {
    return MessageFormat.format(getLocalizedMessage(key), args);
  }

  /** @return Return the set of error messages for the current locale */
  public ResourceBundle getResourceBundle()
  {
    return resourceBundle;
  }

  public static ResourceBundleManager getSingleton(String bundleName)
  {
    if (resourceManagers.get(bundleName) != null)
      return resourceManagers.get(bundleName);

    synchronized(lockObject)
    {
      if (resourceManagers.get(bundleName) != null)
        return resourceManagers.get(bundleName);

      resourceManagers.put(bundleName, new ResourceBundleManager(bundleName));
    }

    return resourceManagers.get(bundleName);
  }

  public Set getKeySet()
  {
    return resourceBundle.keySet();
  }
}