UnpackedObjectTest: Create ObjectInserter.Formatter in try-with-resource

The ObjectInserter.Formatter instance is only used to call idFor.

Factor out a utility method to do that.

Change-Id: I4ef823110c2152ac7905681df3217eb8001f5bd9
Signed-off-by: David Pursehouse <david.pursehouse@sonymobile.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/UnpackedObjectTest.java

 	public void testStandardFormat_LargeObject() throws Exception {
 		final int type = Constants.OBJ_BLOB;
 		byte[] data = getRng().nextBytes(streamThreshold + 5);
-		ObjectId id = new ObjectInserter.Formatter().idFor(type, data);
+		ObjectId id = getId(type, data);
 		write(id, compressStandardFormat(type, data));
 
 		ObjectLoader ol;
 			throws Exception {
 		final int type = Constants.OBJ_BLOB;
 		byte[] data = getRng().nextBytes(streamThreshold + 5);
-		ObjectId id = new ObjectInserter.Formatter().idFor(type, data);
+		ObjectId id = getId(type, data);
 		byte[] gz = compressStandardFormat(type, data);
 		gz[gz.length - 1] = 0;
 		gz[gz.length - 2] = 0;
 			throws Exception {
 		final int type = Constants.OBJ_BLOB;
 		byte[] data = getRng().nextBytes(streamThreshold + 5);
-		ObjectId id = new ObjectInserter.Formatter().idFor(type, data);
+		ObjectId id = getId(type, data);
 		byte[] gz = compressStandardFormat(type, data);
 		byte[] tr = new byte[gz.length - 1];
 		System.arraycopy(gz, 0, tr, 0, tr.length);
 			throws Exception {
 		final int type = Constants.OBJ_BLOB;
 		byte[] data = getRng().nextBytes(streamThreshold + 5);
-		ObjectId id = new ObjectInserter.Formatter().idFor(type, data);
+		ObjectId id = getId(type, data);
 		byte[] gz = compressStandardFormat(type, data);
 		byte[] tr = new byte[gz.length + 1];
 		System.arraycopy(gz, 0, tr, 0, gz.length);
 	public void testPackFormat_LargeObject() throws Exception {
 		final int type = Constants.OBJ_BLOB;
 		byte[] data = getRng().nextBytes(streamThreshold + 5);
-		ObjectId id = new ObjectInserter.Formatter().idFor(type, data);
+		ObjectId id = getId(type, data);
 		write(id, compressPackFormat(type, data));
 
 		ObjectLoader ol;
 			out.close();
 		}
 	}
+
+	private ObjectId getId(int type, byte[] data) {
+		try (ObjectInserter.Formatter formatter = new ObjectInserter.Formatter()) {
+			return formatter.idFor(type, data);
+		}
+	}
 }