CascadingClassLoadHelper.cs :  » Business-Application » Quartz-Enterprise-Scheduler » Quartz » Simpl » C# / CSharp Open Source

/* 
* Copyright 2004-2009 James House 
* 
* 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.
* 
*/

/*
* Previously Copyright (c) 2001-2004 James House
*/
using System;
using System.Collections;
using System.IO;

using Quartz.Simpl;
using Quartz.Spi;

namespace Quartz.Simpl{
  /// <summary>
  /// A <see cref="ITypeLoadHelper" /> uses all of the <see cref="ITypeLoadHelper" />
  /// types that are found in this package in its attempts to load a class, when
  /// one scheme is found to work, it is promoted to the scheme that will be used
  /// first the next time a class is loaded (in order to improve perfomance).
  /// </summary>
  /// <remarks>
  /// This approach is used because of the wide variance in class loader behavior
  /// between the various environments in which Quartz runs (e.g. disparate 
  /// application servers, stand-alone, mobile devices, etc.).  Because of this
  /// disparity, Quartz ran into difficulty with a one class-load style fits-all 
  /// design.  Thus, this class loader finds the approach that works, then 
  /// 'remembers' it.  
  /// </remarks>
  /// <author>James House</author>
  public class CascadingClassLoadHelper : ITypeLoadHelper
  {
    /*
    * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    * 
    * Data members.
    * 
    * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    */

    private ArrayList loadHelpers;

    private ITypeLoadHelper bestCandidate;


    /// <summary> 
    /// Called to give the ClassLoadHelper a chance to Initialize itself,
    /// including the oportunity to "steal" the class loader off of the calling
    /// thread, which is the thread that is initializing Quartz.
    /// </summary>
    public virtual void Initialize()
    {
      loadHelpers = new ArrayList();

      loadHelpers.Add(new LoadingLoaderClassLoadHelper());
      loadHelpers.Add(new SimpleClassLoadHelper());

      foreach (ITypeLoadHelper helper in loadHelpers)
      {
        helper.Initialize();
      }
    }

    /// <summary>
    /// Return the class with the given name.
    /// </summary>
    public virtual Type LoadType(string name)
    {
      if (bestCandidate != null)
      {
        try
        {
          return bestCandidate.LoadType(name);
        }
        catch (Exception)
        {
          bestCandidate = null;
        }
      }

      Exception cnfe = null;
      Type clazz = null;

      foreach (ITypeLoadHelper loadHelper in loadHelpers)
      {
        try
        {
          clazz = loadHelper.LoadType(name);
          if (clazz != null)
          {
            break;
          }
          bestCandidate = loadHelper;
        }
        catch (Exception e)
        {
          cnfe = e;
        }
      }

      if (clazz == null)
      {
                if (cnfe == null)
                {
                    cnfe = new Exception("Could not load requested type: " + name);
                }

        throw cnfe;
      }

      return clazz;
    }

    /// <summary> Finds a resource with a given name. This method returns null if no
    /// resource with this name is found.
    /// </summary>
    /// <param name="name">name of the desired resource
    /// </param>
    /// <returns> a java.net.URL object
    /// </returns>
    public virtual Uri GetResource(string name)
    {
      if (bestCandidate != null)
      {
        try
        {
          return bestCandidate.GetResource(name);
        }
        catch (Exception)
        {
          bestCandidate = null;
        }
      }

      Uri result = null;
      ITypeLoadHelper loadHelper = null;

      foreach (ITypeLoadHelper lh in loadHelpers)
      {
        loadHelper = lh;

        result = loadHelper.GetResource(name);
        if (result != null)
        {
          break;
        }
      }

      bestCandidate = loadHelper;
      return result;
    }

    /// <summary> Finds a resource with a given name. This method returns null if no
    /// resource with this name is found.
    /// </summary>
    /// <param name="name">name of the desired resource
    /// </param>
    /// <returns> a java.io.InputStream object
    /// </returns>
    public virtual Stream GetResourceAsStream(string name)
    {
      if (bestCandidate != null)
      {
        try
        {
          return bestCandidate.GetResourceAsStream(name);
        }
        catch (Exception)
        {
          bestCandidate = null;
        }
      }

      Stream result = null;
      ITypeLoadHelper loadHelper = null;

      foreach (ITypeLoadHelper lh in loadHelpers)
      {
        loadHelper = lh;

        result = loadHelper.GetResourceAsStream(name);
        if (result != null)
        {
          break;
        }
      }

      bestCandidate = loadHelper;
      return result;
    }
  }
}