StoreDataAccessor


1   /**
2    * com.mckoi.store.StoreDataAccessor  10 Jun 2003
3    *
4    * Mckoi SQL Database ( http://www.mckoi.com/database )
5    * Copyright (C) 2000, 2001, 2002  Diehl and Associates, Inc.
6    *
7    * This program is free software; you can redistribute it and/or
8    * modify it under the terms of the GNU General Public License
9    * Version 2 as published by the Free Software Foundation.
10   *
11   * This program is distributed in the hope that it will be useful,
12   * but WITHOUT ANY WARRANTY; without even the implied warranty of
13   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   * GNU General Public License Version 2 for more details.
15   *
16   * You should have received a copy of the GNU General Public License
17   * Version 2 along with this program; if not, write to the Free Software
18   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
19   *
20   * Change Log:
21   * 
22   * 
23   */
24  
25  package com.mckoi.store;
26  
27  import java.io.IOException  ;
28  
29  /**
30   * An interface for low level store data access methods.  This is used to
31   * implement a variety of ways of accessing data from some resource, such as
32   * a file in a filesystem.  For example, we might use this to access a file
33   * using the NIO API, or through the IO API.  Alternatively we may use it to
34   * implement a scattering store that includes data across multiple files in the
35   * filesystem.
36   *
37   * @author Tobias Downer
38   */
39  
40  interface StoreDataAccessor {
41  
42    /**
43     * Returns true if the resource exists.
44     */
45    boolean exists();
46    
47    /**
48     * Deletes the data area resource.  Returns true if the delete was successful.
49     */
50    boolean delete();
51  
52    /**
53     * Opens the underlying data area representation.  If the resource doesn't
54     * exist then it is created and the size is set to 0.
55     */
56    void open(boolean read_only) throws IOException  ;
57    
58    /**
59     * Closes the underlying data area representation.
60     */
61    void close() throws IOException  ;
62  
63  
64    /**
65     * Reads a block of data from the underlying data area at the given position
66     * into the byte array at the given offset.
67     */
68    void read(long position, byte[] buf, int off, int len) throws IOException  ;
69  
70    /**
71     * Writes a block of data to the underlying data area from the byte array at
72     * the given offset.
73     */
74    void write(long position, byte[] buf, int off, int len) throws IOException  ;
75  
76    /**
77     * Sets the size of the underlying data area to the given size.  If the size
78     * of the data area is increased, the content between the old size and the
79     * new size is implementation defined.
80     */
81    void setSize(long new_size) throws IOException  ;
82  
83    /**
84     * Returns the current size of the underlying data area.
85     */
86    long getSize() throws IOException  ;
87    
88    /**
89     * Synchronizes the data area by forcing any data out of the OS buffers onto
90     * the disk.
91     */
92    void synch() throws IOException  ;
93  
94  
95  }
96  
97
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