Can anyone please provide a sample java client which will get all the attributes and the values of the specified workitem

You can get at the built in attributes from somewhere else:

		log("WorkItem: " + workItem.getId() + " "
				+ workItem.getHTMLSummary().getPlainText() + "\t Type "
				+ workItemType.getDisplayName() + "\n");
		List builtInAttributeHandles = getWorkItemClient()
				.findBuiltInAttributes(fProjectArea, monitor);
		IFetchResult builtIn = getTeamRepository().itemManager()
				.fetchCompleteItemsPermissionAware(builtInAttributeHandles,
						IItemManager.REFRESH, monitor);
		List custAttributeHandles = workItem
				.getCustomAttributes();
		IFetchResult custom = getTeamRepository().itemManager()
				.fetchCompleteItemsPermissionAware(custAttributeHandles,
						IItemManager.REFRESH, monitor);
		log(builtIn.getMissingItems().size() + " "
				+ builtIn.getNotFoundItems().size() + " "
				+ builtIn.getPermissionDeniedItems().size() + " "
				+ builtIn.getRetrievedItems().size() + "\n");
		printAttributes(workItem, builtIn.getRetrievedItems());
		printAttributes(workItem, custom.getRetrievedItems());

You can find more information about e.g. casting here: https://rsjazz.wordpress.com/2013/03/20/understanding-and-using-the-rtc-java-client-api/

List<IAttributeHandle> customAttributeHandles = workitem
                .getCustomAttributes();
        for (IAttributeHandle attributeHandle : customAttributeHandles) {
            IAttribute attribute = (IAttribute) teamRepository.itemManager()
                    .fetchCompleteItem(attributeHandle, IItemManager.DEFAULT,
                            null);
            //.... do something with attribute.
        }

Please note that this only fetches custom attributes.
I'm not sure if it's possible to fetch all attributes. You normally access built-in attributes, by their individual getters and setters, for example:
workitem.getDueDate(...)