Implement a rudimentary RandomAccessFile#getChannel

This implementation is by no means intended to be complete, just enough to
support running http://http://loci.wisc.edu/software/bio-formats's
loci.formats.tools.ImageConverter tool.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

classpath/java/io/RandomAccessFile.java

@@ -11,6 +11,8 @@
 package java.io;
 
 import java.lang.IllegalArgumentException;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
 
 public class RandomAccessFile {
   private long peer;
@@ -147,4 +149,50 @@ public class RandomAccessFile {
   }
 
   private static native void close(long peer);
+
+  public FileChannel getChannel() {
+    return new FileChannel() {
+      public void close() {
+        if (peer != 0) RandomAccessFile.close(peer);
+      }
+
+      public boolean isOpen() {
+        return peer != 0;
+      }
+
+      public int read(ByteBuffer dst, long position) throws IOException {
+        if (!dst.hasArray()) throw new IOException("Cannot handle " + dst.getClass());
+	// TODO: this needs to be synchronized on the Buffer, no?
+        byte[] array = dst.array();
+        return readBytes(peer, position, array, dst.position(), dst.remaining());
+      }
+
+      public int read(ByteBuffer dst) throws IOException {
+        int count = read(dst, position);
+        if (count > 0) position += count;
+        return count;
+      }
+
+      public int write(ByteBuffer src, long position) throws IOException {
+        if (!src.hasArray()) throw new IOException("Cannot handle " + src.getClass());
+        byte[] array = src.array();
+        return writeBytes(peer, position, array, src.position(), src.remaining());
+      }
+
+      public int write(ByteBuffer src) throws IOException {
+        int count = write(src, position);
+        if (count > 0) position += count;
+        return count;
+      }
+
+      public long position() throws IOException {
+        return getFilePointer();
+      }
+
+      public FileChannel position(long position) throws IOException {
+        seek(position);
+        return this;
+      }
+    };
+  }
 }