1 files changed, 135 insertions, 0 deletions
diff --git a/src/java/com/healthmarketscience/jackcess/PageChannel.java b/src/java/com/healthmarketscience/jackcess/PageChannel.java
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+++ b/src/java/com/healthmarketscience/jackcess/PageChannel.java
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+/*
+Copyright (c) 2005 Health Market Science, Inc.
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License as published by the Free Software Foundation; either
+version 2.1 of the License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
+USA
+
+You can contact Health Market Science at info@healthmarketscience.com
+or at the following address:
+
+Health Market Science
+2700 Horizon Drive
+Suite 200
+King of Prussia, PA 19406
+*/
+
+package com.healthmarketscience.jackcess;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.channels.Channel;
+import java.nio.channels.FileChannel;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * Reads and writes individual pages in a database file
+ * @author Tim McCune
+ */
+public class PageChannel implements Channel {
+  
+  private static final Log LOG = LogFactory.getLog(PageChannel.class);
+  
+  /** Global usage map always lives on page 1 */
+  private static final int PAGE_GLOBAL_USAGE_MAP = 1;
+  
+  /** Channel containing the database */
+  private FileChannel _channel;
+  /** Format of the database in the channel */
+  private JetFormat _format;
+  /** Tracks free pages in the database. */
+  private UsageMap _globalUsageMap;
+  
+  /**
+   * @param channel Channel containing the database
+   * @param format Format of the database in the channel
+   */
+  public PageChannel(FileChannel channel, JetFormat format) throws IOException {
+    _channel = channel;
+    _format = format;
+    //Null check only exists for unit tests.  Channel should never normally be null.
+    if (channel != null) {
+      _globalUsageMap = UsageMap.read(this, PAGE_GLOBAL_USAGE_MAP, (byte) 0, format);
+    }
+  }
+  
+  /**
+   * @param buffer Buffer to read the page into
+   * @param pageNumber Number of the page to read in (starting at 0)
+   * @return True if the page was successfully read into the buffer, false if
+   *    that page doesn't exist.
+   */
+  public boolean readPage(ByteBuffer buffer, int pageNumber) throws IOException {
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Reading in page " + Integer.toHexString(pageNumber));
+    }
+    buffer.clear();
+    boolean rtn = _channel.read(buffer, (long) pageNumber * (long) _format.PAGE_SIZE) != -1;
+    buffer.flip();
+    return rtn;
+  }
+  
+  /**
+   * Write a page to disk
+   * @param page Page to write
+   * @param pageNumber Page number to write the page to
+   */
+  public void writePage(ByteBuffer page, int pageNumber) throws IOException {
+    page.rewind();
+    _channel.write(page, (long) pageNumber * (long) _format.PAGE_SIZE);
+    _channel.force(true);
+  }
+  
+  /**
+   * Write a page to disk as a new page, appending it to the database
+   * @param page Page to write
+   * @return Page number at which the page was written
+   */
+  public int writeNewPage(ByteBuffer page) throws IOException {
+    long size = _channel.size();
+    page.rewind();
+    _channel.write(page, size);
+    int pageNumber = (int) (size / _format.PAGE_SIZE);
+    _globalUsageMap.removePageNumber(pageNumber);  //force is done here
+    return pageNumber;
+  }
+  
+  /**
+   * @return Number of pages in the database
+   */
+  public int getPageCount() throws IOException {
+    return (int) (_channel.size() / _format.PAGE_SIZE);
+  }
+  
+  /**
+   * @return A newly-allocated buffer that can be passed to readPage
+   */
+  public ByteBuffer createPageBuffer() {
+    ByteBuffer rtn = ByteBuffer.allocate(_format.PAGE_SIZE);
+    rtn.order(ByteOrder.LITTLE_ENDIAN);
+    return rtn;
+  }
+  
+  public void close() throws IOException {
+    _channel.force(true);
+    _channel.close();
+  }
+  
+  public boolean isOpen() {
+    return _channel.isOpen();
+  }
+  
+}