DataHandle: add exists() method

Author: ctrueden

src/main/java/org/scijava/io/handle/BytesHandle.java

@@ -63,6 +63,11 @@ public boolean isWritable() {
 		return !bytes().isReadOnly();
 	}
 
+	@Override
+	public boolean exists() {
+		return true;
+	}
+
 	@Override
 	public long offset() {
 		return offset;

src/main/java/org/scijava/io/handle/DataHandle.java

@@ -71,6 +71,14 @@ public enum ByteOrder {
 	/** Gets whether writing to this handle is supported. */
 	boolean isWritable();
 
+	/**
+	 * Tests whether this handle's location actually exists at the source.
+	 * 
+	 * @return True if the location exists; false if not.
+	 * @throws IOException If something goes wrong with the existence check.
+	 */
+	boolean exists() throws IOException;
+
 	/** Returns the current offset in the stream. */
 	long offset() throws IOException;
 

src/main/java/org/scijava/io/handle/DummyHandle.java

@@ -63,6 +63,11 @@ public boolean isWritable() {
 		return true;
 	}
 
+	@Override
+	public boolean exists() {
+		return true;
+	}
+
 	@Override
 	public long offset() {
 		return offset;
@@ -133,5 +138,4 @@ public void close() {
 	public Class<DummyLocation> getType() {
 		return DummyLocation.class;
 	}
-
 }

src/main/java/org/scijava/io/handle/FileHandle.java

@@ -84,6 +84,11 @@ public boolean isWritable() {
 		return getMode().contains("w");
 	}
 
+	@Override
+	public boolean exists() {
+		return get().getFile().exists();
+	}
+
 	@Override
 	public long offset() throws IOException {
 		return raf().getFilePointer();
@@ -299,5 +304,4 @@ private synchronized void initRAF() throws IOException {
 		if (raf != null) return;
 		raf = new RandomAccessFile(get().getFile(), getMode());
 	}
-
 }