Tweak NPOIFS constructors so that if you have a FileChannel, you can pass it in, but that the File based one will tidy up after itself in the event of errors

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1054033 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/poifs/filesystem/NPOIFSFileSystem.java

@@ -107,7 +107,7 @@ public class NPOIFSFileSystem extends BlockStore
 
     /**
      * Creates a POIFSFileSystem from a <tt>File</tt>. This uses less memory than
-     *  creating from an <tt>InputStream</tt>.
+     *  creating from an <tt>InputStream</tt>. The File will be opened read-only
      *  
      * Note that with this constructor, you will need to call {@link #close()}
      *  when you're done to have the underlying file closed, as the file is
@@ -119,12 +119,55 @@ public class NPOIFSFileSystem extends BlockStore
      */
     public NPOIFSFileSystem(File file)
          throws IOException
+    {
+       this(file, true);
+    }
+    
+    /**
+     * Creates a POIFSFileSystem from a <tt>File</tt>. This uses less memory than
+     *  creating from an <tt>InputStream</tt>.
+     *  
+     * Note that with this constructor, you will need to call {@link #close()}
+     *  when you're done to have the underlying file closed, as the file is
+     *  kept open during normal operation to read the data out. 
+     *  
+     * @param file the File from which to read the data
+     *
+     * @exception IOException on errors reading, or on invalid data
+     */
+    public NPOIFSFileSystem(File file, boolean readOnly)
+         throws IOException
+    {
+       this(
+           (new RandomAccessFile(file, readOnly? "r" : "rw")).getChannel(),
+           true
+       );
+    }
+    
+    /**
+     * Creates a POIFSFileSystem from an open <tt>FileChannel</tt>. This uses 
+     *  less memory than creating from an <tt>InputStream</tt>.
+     *  
+     * Note that with this constructor, you will need to call {@link #close()}
+     *  when you're done to have the underlying Channel closed, as the channel is
+     *  kept open during normal operation to read the data out. 
+     *  
+     * @param channel the FileChannel from which to read the data
+     *
+     * @exception IOException on errors reading, or on invalid data
+     */
+    public NPOIFSFileSystem(FileChannel channel)
+         throws IOException
+    {
+       this(channel, false);
+    }
+    
+    private NPOIFSFileSystem(FileChannel channel, boolean closeChannelOnError)
+         throws IOException
     {
        this();
 
-       // Open the underlying channel
+       try {
-       FileChannel channel = (new RandomAccessFile(file, "r")).getChannel();
-       
           // Get the header
           ByteBuffer headerBuffer = ByteBuffer.allocate(POIFSConstants.SMALLER_BIG_BLOCK_SIZE);
           IOUtils.readFully(channel, headerBuffer);
@@ -135,6 +178,12 @@ public class NPOIFSFileSystem extends BlockStore
           // Now process the various entries
           _data = new FileBackedDataSource(channel);
           readCoreContents();
+       } catch(IOException e) {
+          if(closeChannelOnError) {
+             channel.close();
+          }
+          throw e;
+       }
     }
     
     /**