AbstractDataSourceBlockIdGenerator


1   /* 
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *   http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed  under the  License is distributed on an "AS IS" BASIS,
13   * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
14   * implied.
15   * 
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  
20  package org.apache.avalon.excalibur.datasource.ids;
21  
22  import java.math.BigDecimal  ;
23  
24  import org.apache.avalon.framework.configuration.Configuration;
25  import org.apache.avalon.framework.configuration.ConfigurationException;
26  
27  /**
28   * The AbstractDataSourceBlockIdGenerator allocates blocks of ids from a DataSource
29   *  and then provides them as needed.  This is useful in reducing communication with
30   *  the DataSource.
31   *
32   * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
33   * @version CVS $Revision: 1.4 $ $Date: 2004/02/28 11:47:17 $
34   * @since 4.1
35   */
36  public abstract class AbstractDataSourceBlockIdGenerator
37      extends AbstractDataSourceIdGenerator
38  {
39      /**
40       * The first id in a batch of Ids loaded in from the DataSource.
41       */
42      private BigDecimal   m_firstBigDecimal;
43  
44      /**
45       * The first id in a batch of Ids loaded in from the DataSource.
46       */
47      private long m_firstLong;
48  
49      /**
50       * The number of ids loaded in each block.
51       */
52      private int m_blockSize;
53  
54      /**
55       * The number of ids which have been allocated from the current block.
56       */
57      private int m_allocated;
58  
59      /*---------------------------------------------------------------
60       * Constructors
61       *-------------------------------------------------------------*/
62      public AbstractDataSourceBlockIdGenerator()
63      {
64      }
65  
66      /*---------------------------------------------------------------
67       * Methods
68       *-------------------------------------------------------------*/
69      /**
70       * Allocates a block, of the given size, of ids from the database.
71       *
72       * @param blockSize number of Ids which are to be allocated.
73       *
74       * @return The first id in the allocated block.
75       *
76       * @throws IdException if there it was not possible to allocate a block of ids.
77       */
78      protected abstract BigDecimal   allocateBigDecimalIdBlock( int blockSize )
79          throws IdException;
80  
81      /**
82       * Allocates a block, of the given size, of ids from the database.
83       *
84       * @param blockSize number of Ids which are to be allocated.
85       *
86       * @return The first id in the allocated block.
87       *
88       * @throws IdException if there it was not possible to allocate a block of ids.
89       */
90      protected abstract long allocateLongIdBlock( int blockSize )
91          throws IdException;
92  
93      /*---------------------------------------------------------------
94       * AbstractIdGenerator Methods
95       *-------------------------------------------------------------*/
96      /**
97       * Gets the next id as a Big Decimal.  This method will only be called
98       *  when synchronized and when the data type is configured to be BigDecimal.
99       *
100      * @return the next id as a BigDecimal.
101      *
102      * @throws IdException if an Id could not be allocated for any reason.
103      */
104     protected BigDecimal   getNextBigDecimalIdInner()
105         throws IdException
106     {
107         if( m_allocated >= m_blockSize )
108         {
109             // Need to allocate a new batch of ids
110             try
111             {
112                 m_firstBigDecimal = allocateBigDecimalIdBlock( m_blockSize );
113 
114                 // Reset the allocated count
115                 m_allocated = 0;
116             }
117             catch( IdException e )
118             {
119                 // Set the allocated count to signal that there are not any ids available.
120                 m_allocated = Integer.MAX_VALUE;
121                 throw e;
122             }
123         }
124 
125         // We know that at least one id is available.
126         // Get an id out of the currently allocated block.
127         BigDecimal   id = m_firstBigDecimal.add( new BigDecimal  ( m_allocated ) );
128         m_allocated++;
129 
130         return id;
131     }
132 
133     /**
134      * Gets the next id as a long.  This method will only be called
135      *  when synchronized and when the data type is configured to be long.
136      *
137      * @return the next id as a long.
138      *
139      * @throws IdException if an Id could not be allocated for any reason.
140      */
141     protected long getNextLongIdInner()
142         throws IdException
143     {
144         if( m_allocated >= m_blockSize )
145         {
146             // Need to allocate a new batch of ids
147             try
148             {
149                 m_firstLong = allocateLongIdBlock( m_blockSize );
150 
151                 // Reset the allocated count
152                 m_allocated = 0;
153             }
154             catch( IdException e )
155             {
156                 // Set the allocated count to signal that there are not any ids available.
157                 m_allocated = Integer.MAX_VALUE;
158                 throw e;
159             }
160         }
161 
162         // We know that at least one id is available.
163         // Get an id out of the currently allocated block.
164         long id = m_firstLong + m_allocated;
165         if( id < 0 )
166         {
167             // The value wrapped
168             String   msg = "No more Ids are available, the maximum long value has been reached.";
169             getLogger().error( msg );
170             throw new IdException( msg );
171         }
172         m_allocated++;
173 
174         return id;
175     }
176 
177     /*---------------------------------------------------------------
178      * Configurable Methods
179      *-------------------------------------------------------------*/
180     /**
181      * Called by the Container to configure the component.
182      *
183      * @param configuration configuration info used to setup the component.
184      *
185      * @throws ConfigurationException if there are any problems with the configuration.
186      */
187     public void configure( Configuration configuration )
188         throws ConfigurationException
189     {
190         super.configure( configuration );
191 
192         // Obtain the block size.
193         m_blockSize = configuration.getAttributeAsInteger( "block-size", 10 );
194     }
195 
196     /*---------------------------------------------------------------
197      * Initializable Methods
198      *-------------------------------------------------------------*/
199     /**
200      * Called by the Container to initialize the component.
201      *
202      * @throws Exception if there were any problems durring initialization.
203      */
204     public void initialize()
205         throws Exception  
206     {
207         super.initialize();
208 
209         // Set the state so that the first request for an id will load in a block of ids.
210         m_allocated = Integer.MAX_VALUE;
211     }
212 }
213 
214
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