How to add attachment to workitem by JAVA API?

	/**
	 * Utility method to upload and attach a file to a work item
	 * 
	 * @param fileName
	 *            - the file name of the file to upload
	 * @param description
	 *            - the description of the attachment
	 * @param contentType
	 *            - the content type of the file
	 * @param encoding
	 *            - the encoding of the file
	 * 
	 * @throws TeamRepositoryException
	 */
	private void attachFile(String fileName, String description,
			String contentType, String encoding) throws TeamRepositoryException {

		File attachmentFile = new File(fileName);
		FileInputStream fis;
		try {
			fis = new FileInputStream(attachmentFile);
			try {
				IAttachment newAttachment = getWorkItemClient()
						.createAttachment(getWorkItem().getProjectArea(),
								attachmentFile.getName(), description,
								contentType, encoding, fis, monitor);

				newAttachment = (IAttachment) newAttachment.getWorkingCopy();
				newAttachment = getWorkItemCommon().saveAttachment(
						newAttachment, monitor);
				IItemReference reference = WorkItemLinkTypes
						.createAttachmentReference(newAttachment);

				getWorkingCopy().getReferences().add(
						WorkItemEndPoints.ATTACHMENT, reference);

			} finally {
				if (fis != null) {
					fis.close();
				}
			}
		} catch (FileNotFoundException e) {
			throw new WorkItemCommandLineException(
					"Attach File - File not found: " + fileName, e);
		} catch (IOException e) {
			throw new WorkItemCommandLineException(
					"Attach File - I/O Exception: " + fileName, e);
		}
	}