PerThreadSingleton xref

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    1   /*
    2    * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
    3    *
    4    * This software is open source.
    5    * See the bottom of this file for the licence.
    6    */
    7
    8   package org.dom4j.util;
    9
    10  import java.lang.ref.WeakReference;
    11
    12  /***
    13   * <p>
    14   * <code>PerThreadSingleton</code> is an implementation of the
    15   * SingletonStrategy used to provide common factory access to a single object
    16   * instance based on an implementation strategy for one object instance per
    17   * thread. This is useful in replace of the ThreadLocal usage.
    18   * </p>
    19   *
    20   * @author <a href="mailto:ddlucas@users.sourceforge.net">David Lucas </a>
    21   * @version $Revision: 1.3 $
    22   */
    23
    24  public class PerThreadSingleton implements SingletonStrategy {
    25      private String singletonClassName = null;
    26
    27      private ThreadLocal perThreadCache = new ThreadLocal();
    28
    29      public PerThreadSingleton() {
    30      }
    31
    32      public void reset() {
    33          perThreadCache = new ThreadLocal();
    34      }
    35
    36      public Object instance() {
    37          Object singletonInstancePerThread = null;
    38          // use weak reference to prevent cyclic reference during GC
    39          WeakReference ref = (WeakReference) perThreadCache.get();
    40          // singletonInstancePerThread=perThreadCache.get();
    41          // if (singletonInstancePerThread==null) {
    42          if (ref == null || ref.get() == null) {
    43              Class clazz = null;
    44              try {
    45                  clazz = Thread.currentThread().getContextClassLoader().loadClass(
    46                          singletonClassName);
    47                  singletonInstancePerThread = clazz.newInstance();
    48              } catch (Exception ignore) {
    49                  try {
    50                      clazz = Class.forName(singletonClassName);
    51                      singletonInstancePerThread = clazz.newInstance();
    52                  } catch (Exception ignore2) {
    53                  }
    54              }
    55              perThreadCache.set(new WeakReference(singletonInstancePerThread));
    56          } else {
    57              singletonInstancePerThread = ref.get();
    58          }
    59          return singletonInstancePerThread;
    60      }
    61
    62      public void setSingletonClassName(String singletonClassName) {
    63          this.singletonClassName = singletonClassName;
    64      }
    65
    66  }
    67
    68  /*
    69   * Redistribution and use of this software and associated documentation
    70   * ("Software"), with or without modification, are permitted provided that the
    71   * following conditions are met:
    72   *
    73   * 1. Redistributions of source code must retain copyright statements and
    74   * notices. Redistributions must also contain a copy of this document.
    75   *
    76   * 2. Redistributions in binary form must reproduce the above copyright notice,
    77   * this list of conditions and the following disclaimer in the documentation
    78   * and/or other materials provided with the distribution.
    79   *
    80   * 3. The name "DOM4J" must not be used to endorse or promote products derived
    81   * from this Software without prior written permission of MetaStuff, Ltd. For
    82   * written permission, please contact dom4j-info@metastuff.com.
    83   *
    84   * 4. Products derived from this Software may not be called "DOM4J" nor may
    85   * "DOM4J" appear in their names without prior written permission of MetaStuff,
    86   * Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
    87   *
    88   * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
    89   *
    90   * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND
    91   * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    92   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    93   * ARE DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE
    94   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    95   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    96   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    97   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    98   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    99   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    100  * POSSIBILITY OF SUCH DAMAGE.
    101  *
    102  * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
    103  */