Home | History | Annotate | Download | only in utils 
      1 /*
      2  * Licensed to the Apache Software Foundation (ASF) under one
      3  * or more contributor license agreements. See the NOTICE file
      4  * distributed with this work for additional information
      5  * regarding copyright ownership. The ASF licenses this file
      6  * to you under the Apache License, Version 2.0 (the  "License");
      7  * you may not use this file except in compliance with the License.
      8  * You may obtain a copy of the License at
      9  *
     10  *     http://www.apache.org/licenses/LICENSE-2.0
     11  *
     12  * Unless required by applicable law or agreed to in writing, software
     13  * distributed under the License is distributed on an "AS IS" BASIS,
     14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15  * See the License for the specific language governing permissions and
     16  * limitations under the License.
     17  */
     18 /*
     19  * $Id: ObjectPool.java 475981 2006-11-16 23:35:53Z minchau $
     20  */
     21 package org.apache.xml.utils;
     22 
     23 import java.util.ArrayList;
     24 
     25 import org.apache.xml.res.XMLErrorResources;
     26 import org.apache.xml.res.XMLMessages;
     27 
     28 
     29 /**
     30  * Pool of object of a given type to pick from to help memory usage
     31  * @xsl.usage internal
     32  */
     33 public class ObjectPool implements java.io.Serializable
     34 {
     35     static final long serialVersionUID = -8519013691660936643L;
     36 
     37   /** Type of objects in this pool.
     38    *  @serial          */
     39   private final Class objectType;
     40 
     41   /** Stack of given objects this points to.
     42    *  @serial          */
     43   private final ArrayList freeStack;
     44 
     45   /**
     46    * Constructor ObjectPool
     47    *
     48    * @param type Type of objects for this pool
     49    */
     50   public ObjectPool(Class type)
     51   {
     52     objectType = type;
     53     freeStack = new ArrayList();
     54   }
     55 
     56   /**
     57    * Constructor ObjectPool
     58    *
     59    * @param className Fully qualified name of the type of objects for this pool.
     60    */
     61   public ObjectPool(String className)
     62   {
     63     try
     64     {
     65       objectType = ObjectFactory.findProviderClass(
     66         className, ObjectFactory.findClassLoader(), true);
     67     }
     68     catch(ClassNotFoundException cnfe)
     69     {
     70       throw new WrappedRuntimeException(cnfe);
     71     }
     72     freeStack = new ArrayList();
     73   }
     74 
     75 
     76   /**
     77    * Constructor ObjectPool
     78    *
     79    *
     80    * @param type Type of objects for this pool
     81    * @param size Size of vector to allocate
     82    */
     83   public ObjectPool(Class type, int size)
     84   {
     85     objectType = type;
     86     freeStack = new ArrayList(size);
     87   }
     88 
     89   /**
     90    * Constructor ObjectPool
     91    *
     92    */
     93   public ObjectPool()
     94   {
     95     objectType = null;
     96     freeStack = new ArrayList();
     97   }
     98 
     99   /**
    100    * Get an instance of the given object in this pool if available
    101    *
    102    *
    103    * @return an instance of the given object if available or null
    104    */
    105   public synchronized Object getInstanceIfFree()
    106   {
    107 
    108     // Check if the pool is empty.
    109     if (!freeStack.isEmpty())
    110     {
    111 
    112       // Remove object from end of free pool.
    113       Object result = freeStack.remove(freeStack.size() - 1);
    114       return result;
    115     }
    116 
    117     return null;
    118   }
    119 
    120   /**
    121    * Get an instance of the given object in this pool
    122    *
    123    *
    124    * @return An instance of the given object
    125    */
    126   public synchronized Object getInstance()
    127   {
    128 
    129     // Check if the pool is empty.
    130     if (freeStack.isEmpty())
    131     {
    132 
    133       // Create a new object if so.
    134       try
    135       {
    136         return objectType.newInstance();
    137       }
    138       catch (InstantiationException ex){}
    139       catch (IllegalAccessException ex){}
    140 
    141       // Throw unchecked exception for error in pool configuration.
    142       throw new RuntimeException(XMLMessages.createXMLMessage(XMLErrorResources.ER_EXCEPTION_CREATING_POOL, null)); //"exception creating new instance for pool");
    143     }
    144     else
    145     {
    146 
    147       // Remove object from end of free pool.
    148       Object result = freeStack.remove(freeStack.size() - 1);
    149 
    150       return result;
    151     }
    152   }
    153 
    154   /**
    155    * Add an instance of the given object to the pool
    156    *
    157    *
    158    * @param obj Object to add.
    159    */
    160   public synchronized void freeInstance(Object obj)
    161   {
    162 
    163     // Make sure the object is of the correct type.
    164     // Remove safety.  -sb
    165     // if (objectType.isInstance(obj))
    166     // {
    167     freeStack.add(obj);
    168     // }
    169     // else
    170     // {
    171     //  throw new IllegalArgumentException("argument type invalid for pool");
    172     // }
    173   }
    174 }
    175