Dynamic Drop Down Menu

Hi,
I want to create drop down menu , as i created succesfully but i want user to select on one drop down menu and depending on selected item from drop down menu one , drop down menu 2 items populated.

Current problem is:

suppose there are two category “Animals” and “Vehicles”, and Sub categories are “CAT”,“DOG”,“BUS”,“CAR” , so right now issue is whatever i select in category it will display all four sub categories but now i want show sub category depending on Category selection.

code snippet right now is:

@General(title = "XYZ Parser", purpose = "Parse XYZ file", author = "NeosAlpha", docLink = "http://neosalpha.com/")
@Outputs(min = 1, max = 1, offers = ViewType.DOCUMENT)
@Errors(min = 1, max = 1, offers = ViewType.DOCUMENT)
@Version(snap = 1)
@Category(snap = SnapCategory.PARSE)
public class XYZParser extends SimpleBinaryWriteSnap implements DependencyManager {

	private static final String FILE_BROWSER_PROP = "file_browser_prop";
	
	private static final String XYZ_TYPE_PROP = "XYZ_type_prop";
	private static final String XYZ_TYPE_PROP_VALUE = "Animals";
	
	private static final String FILE_TYPE_PROP = "file_type_prop";
	private static final String FILE_TYPE_PROP_VALUE = "Vehicles";
	
	private String filePath;

	@Inject
	private DocumentUtility documentUtility;

	@Inject
	private URLEncoder urlEncoder;

	@Inject
	private JfsUtils jfsUtils;

	String fileBrowser;
	String filetype;
	String XYZtype;
	Map<String, Object> composite;

	@Override
	public Module getManagedModule() {
		return new AbstractModule() {
			@Override
			protected void configure() {
				bind(ForEx.class).to(ForExImpl.class);
				bind(JfsUtils.class).toInstance(JfsUtils.getInstance());
			}
		};
	}

	// An optional file selector for providing exchange rates within a file
	@Override
	public void defineProperties(PropertyBuilder propertyBuilder) {

		Set<String> XYZ_set = new HashSet<String>();
		XYZ_set.add("");
		XYZ_set.add("Animals");
		XYZ_set.add("Vehicles");
        Set<String> file_set = new HashSet<String>();
        file_set.add("");
        file_set.add("CAT");
        file_set.add("CAR");
		file_set.add("DOG");
		file_set.add("BUS");
		propertyBuilder.describe(XYZ_TYPE_PROP, "XYZ Type",
				"Write XYZ ")
			.withAllowedValues(XYZ_set)
         .required()
         .add();
		
		propertyBuilder.describe(FILE_TYPE_PROP, "File Type",
				"Write File type ")
		.withAllowedValues(file_set)
        .required()
        .add();
				
	}

	@Override
	public void configure(PropertyValues propertyValues) throws ConfigurationException {
	
		filetype = propertyValues.getAsExpression(FILE_TYPE_PROP).eval(null);
		XYZtype = propertyValues.getAsExpression(XYZ_TYPE_PROP).eval(null);
	}

	@Override
	public void cleanup() throws ExecutionException {
		// TODO Auto-generated method stub

	}

	@Override
	protected void process(final Document document, final ReadableByteChannel readChannel) {
		
		try (InputStream inputStream = Channels.newInputStream(readChannel)) {

		
			if(filetype.contentEquals("Animals") && XYZtype.contentEquals("CAT"))
			{
			
					
				} else {
				
						// PUT ERROR CODE HERE
				
				}
			}
			else if(filetype.contentEquals("Vehicles") && XYZtype.contentEquals("BUS") )
			{
			
			}
			
			 else {
						// Error Code Here
			}

		} catch (IOException e) {
			errorViews.write(new SnapDataException(e, e.getMessage()), document);
			
		} finally {
			

		}

		outputViews.write(documentUtility.newDocument(data),document);

	}

}

What i want is given below:
For example firstly i select category which are “Animals” or “Vehicles”.
Suppose if i select Animals from category dropdown menu then in next dropdown only selections are shown is “CAT” or “DOG”

Suppose if i select Vehicles from category drop down menu then in next drop down only selections are shown is “BUS” or “CAR”

Just give me code snippet i ll do the rest.
Thanks
Nikhil Purohit