| /** |
| * JDBM LICENSE v1.00 |
| * |
| * Redistribution and use of this software and associated documentation |
| * ("Software"), with or without modification, are permitted provided |
| * that the following conditions are met: |
| * |
| * 1. Redistributions of source code must retain copyright |
| * statements and notices. Redistributions must also contain a |
| * copy of this document. |
| * |
| * 2. Redistributions in binary form must reproduce the |
| * above copyright notice, this list of conditions and the |
| * following disclaimer in the documentation and/or other |
| * materials provided with the distribution. |
| * |
| * 3. The name "JDBM" must not be used to endorse or promote |
| * products derived from this Software without prior written |
| * permission of Cees de Groot. For written permission, |
| * please contact cg@cdegroot.com. |
| * |
| * 4. Products derived from this Software may not be called "JDBM" |
| * nor may "JDBM" appear in their names without prior written |
| * permission of Cees de Groot. |
| * |
| * 5. Due credit should be given to the JDBM Project |
| * (http://jdbm.sourceforge.net/). |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS |
| * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT |
| * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND |
| * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL |
| * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT, |
| * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
| * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR |
| * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, |
| * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED |
| * OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| * Copyright 2000 (C) Cees de Groot. All Rights Reserved. |
| * Contributions are Copyright (C) 2000 by their associated contributors. |
| * |
| * $Id: FileHeader.java,v 1.3 2005/06/25 23:12:32 doomdark Exp $ |
| */ |
| |
| package jdbm.recman; |
| |
| /** |
| * This class represents a file header. It is a 1:1 representation of |
| * the data that appears in block 0 of a file. |
| */ |
| class FileHeader implements BlockView { |
| // offsets |
| private static final short O_MAGIC = 0; // short magic |
| private static final short O_LISTS = Magic.SZ_SHORT; // long[2*NLISTS] |
| private static final int O_ROOTS = |
| O_LISTS + (Magic.NLISTS * 2 * Magic.SZ_LONG); |
| |
| // my block |
| private BlockIo block; |
| |
| /** The number of "root" rowids available in the file. */ |
| static final int NROOTS = |
| (RecordFile.BLOCK_SIZE - O_ROOTS) / Magic.SZ_LONG; |
| |
| /** |
| * Constructs a FileHeader object from a block. |
| * |
| * @param block The block that contains the file header |
| * @param isNew If true, the file header is for a new file. |
| * @throws IOException if the block is too short to keep the file |
| * header. |
| */ |
| FileHeader(BlockIo block, boolean isNew) { |
| this.block = block; |
| if (isNew) |
| block.writeShort(O_MAGIC, Magic.FILE_HEADER); |
| else if (!magicOk()) |
| throw new Error("CRITICAL: file header magic not OK " |
| + block.readShort(O_MAGIC)); |
| } |
| |
| /** Returns true if the magic corresponds with the fileHeader magic. */ |
| private boolean magicOk() { |
| return block.readShort(O_MAGIC) == Magic.FILE_HEADER; |
| } |
| |
| |
| /** Returns the offset of the "first" block of the indicated list */ |
| private short offsetOfFirst(int list) { |
| return (short) (O_LISTS + (2 * Magic.SZ_LONG * list)); |
| } |
| |
| /** Returns the offset of the "last" block of the indicated list */ |
| private short offsetOfLast(int list) { |
| return (short) (offsetOfFirst(list) + Magic.SZ_LONG); |
| } |
| |
| /** Returns the offset of the indicated root */ |
| private short offsetOfRoot(int root) { |
| return (short) (O_ROOTS + (root * Magic.SZ_LONG)); |
| } |
| |
| /** |
| * Returns the first block of the indicated list |
| */ |
| long getFirstOf(int list) { |
| return block.readLong(offsetOfFirst(list)); |
| } |
| |
| /** |
| * Sets the first block of the indicated list |
| */ |
| void setFirstOf(int list, long value) { |
| block.writeLong(offsetOfFirst(list), value); |
| } |
| |
| /** |
| * Returns the last block of the indicated list |
| */ |
| long getLastOf(int list) { |
| return block.readLong(offsetOfLast(list)); |
| } |
| |
| /** |
| * Sets the last block of the indicated list |
| */ |
| void setLastOf(int list, long value) { |
| block.writeLong(offsetOfLast(list), value); |
| } |
| |
| /** |
| * Returns the indicated root rowid. A root rowid is a special rowid |
| * that needs to be kept between sessions. It could conceivably be |
| * stored in a special file, but as a large amount of space in the |
| * block header is wasted anyway, it's more useful to store it where |
| * it belongs. |
| * |
| * @see #NROOTS |
| */ |
| long getRoot(int root) { |
| return block.readLong(offsetOfRoot(root)); |
| } |
| |
| /** |
| * Sets the indicated root rowid. |
| * |
| * @see #getRoot |
| * @see #NROOTS |
| */ |
| void setRoot(int root, long rowid) { |
| block.writeLong(offsetOfRoot(root), rowid); |
| } |
| } |