PropertiesUtils

/*
 * $Source$
 * $Revision$
 *
 * Copyright (C) 2000 William Chesters
 *
 * Part of Melati (http://melati.org), a framework for the rapid
 * development of clean, maintainable web applications.
 *
 * Melati is free software; Permission is granted to copy, distribute
 * and/or modify this software under the terms either:
 *
 * a) the GNU General Public License as published by the Free Software
 *    Foundation; either version 2 of the License, or (at your option)
 *    any later version,
 *
 *    or
 *
 * b) any version of the Melati Software License, as published
 *    at http://melati.org
 *
 * You should have received a copy of the GNU General Public License and
 * the Melati Software License along with this program;
 * if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA to obtain the
 * GNU General Public License and visit http://melati.org to obtain the
 * Melati Software License.
 *
 * Feel free to contact the Developers of Melati (http://melati.org),
 * if you would like to work out a different arrangement than the options
 * outlined here.  It is our intention to allow Melati to be used by as
 * wide an audience as possible.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * Contact details for copyright holder:
 *
 *     William Chesters <williamc AT paneris.org>
 *     http://paneris.org/~williamc
 *     Obrechtstraat 114, 2517VX Den Haag, The Netherlands
 */

package org.melati.util;

import java.util.Hashtable;
import java.util.Properties;
import java.io.File;
import java.io.InputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.FileNotFoundException;

/**
 * Useful things to do with properties files.
 */
public final class PropertiesUtils {

  private PropertiesUtils() {}

  /**
   * Get a {@link Properties} object from a file.
   *
   * @param path a {@link File} path name
   * @return a {@link Properties} object
   * @throws IOException if there is a problem loading the file
   */
  public static Properties fromFile(File path) throws IOException {
    InputStream data = new FileInputStream(path);
    Properties them = new Properties();
    try {
      them.load(data);
    } catch (IOException e) {
      throw new IOException("Corrupt properties file `" + path + "': " +
      e.getMessage());
    }

    return them;
  }

  public static Properties fromResource(Class<?> clazz)
        throws IOException {
    String name = clazz.getCanonicalName() + ".properties";
    return fromResource(clazz, name);
  }

  /**
   * Get a {@link Properties} object from a {@link Class}.
   *
   *
   * @param clazz the {@link Class} to look up
   * @param name the property file name
   * @return a {@link Properties} object
   * @throws IOException if the file cannot load or is not found
   */
  public static Properties fromResource(Class<?> clazz, String name)
      throws IOException {
    InputStream is = clazz.getResourceAsStream(name);

    if (is == null)
      throw new FileNotFoundException(name + ": is it in CLASSPATH?");

    Properties them = new Properties();
    try {
      them.load(is);
    } catch (IOException e) {
      throw new IOException("Corrupt properties file `" + name + "': " +
      e.getMessage());
    }

    return them;
  }

  /**
   * Return a property.
   *
   * @param properties the {@link Properties} object to look in
   * @param propertyName the property to get
   * @return the property value
   * @throws NoSuchPropertyException if the property is not set
   */
  public static String getOrDie(Properties properties, String propertyName)
      throws NoSuchPropertyException {
    String value = properties.getProperty(propertyName);
    if (value == null)
      throw new NoSuchPropertyException(properties, propertyName);
    return value;
  }

  /**
   * Get a property or return the supplied default.
   *
   * @param properties the {@link Properties} object to look in
   * @param propertyName the property to get
   * @param def the default to return if not found
   * @return the property value
   */
  public static String getOrDefault(Properties properties,
                                    String propertyName, String def) {
    String value = properties.getProperty(propertyName);
    if (value == null) return def;
    return value;
  }

  /**
   * Get an Integer property.
   *
   * @param properties the {@link Properties} object to look in
   * @param propertyName the property to get
   * @return the int property value
   * @throws NoSuchPropertyException if it is not found
   * @throws FormatPropertyException if it is not an Integer
   */
  public static int getOrDie_int(Properties properties, String propertyName)
      throws NoSuchPropertyException, FormatPropertyException {
    String string = getOrDie(properties, propertyName);
    try {
      return Integer.parseInt(string);
    }
    catch (NumberFormatException e) {
      throw new FormatPropertyException(properties, propertyName, string,
      "an integer", e);
    }
  }

  /**
   * Get an Integer property from a {@link Properties} object or make a fuss.
   *
   * @param properties a {@link Properties}
   * @param propertyName the name of the property
   * @param def cater for multiple definitions, with increment numbers
   * @return the property as an int
   * @throws FormatPropertyException if it is not an Integer
   */
  public static int getOrDefault_int(Properties properties,
                                     String propertyName, int def)
      throws FormatPropertyException {
    String string = getOrDefault(properties, propertyName, ""+def);
    try {
      return Integer.parseInt(string);
    }
    catch (NumberFormatException e) {
      throw new FormatPropertyException(properties, propertyName, string,
      "an integer", e);
    }
  }

  private static Hashtable<String, Object> instantiatedClassesCache = new Hashtable<String, Object>();
  /**
   * Instantiate an interface.
   *
   * @param className the name of the class
   * @param interfaceClassName the interface Class name
   * @return a new object
   * @throws InstantiationPropertyException
   *   if the named class does not descend from the interface
   */
  public static Object instanceOfNamedClass(String className, String interfaceClassName)
      throws InstantiationPropertyException {
    Object cached = instantiatedClassesCache.get(className);
    if (cached != null)
      return cached;
    try {
      Class<?> clazz = Class.forName(className);
      if (interfaceClassName != null) {
        Class<?> interfaceClass = Class.forName(interfaceClassName);
        if (!interfaceClass.isAssignableFrom(clazz))
          throw new ClassCastException(
                clazz + " is not descended from " + interfaceClass);
      }
      Object it = clazz.newInstance();
      instantiatedClassesCache.put(className, it);
      return it;
    } catch (Exception e) {
      throw new InstantiationPropertyException(className, e);
    }
  }

  /**
   * Instantiate a Class.
   *
   * @param properties a {@link Properties}
   * @param propertyName the name of the property
   * @param interfaceClassName     the interface name
   * @param defaultName  a default concrete class if the property is undefined
   * @return a new Object
   * @throws InstantiationPropertyException if there is a problem
   */
  public static Object instanceOfNamedClass(Properties properties,
                                            String propertyName,
                                            String interfaceClassName,
                                            String defaultName)
  throws InstantiationPropertyException {
    String className =  (String)properties.get(propertyName);
    return instanceOfNamedClass(className == null ? defaultName : className, interfaceClassName);
  }
}