XML/JSON symmetric REST web services providers for Jersey

Many times I’ve been asked to provide a set of Web Services interfaces where both JSON and XML clients can communicate with the server. Primarily it’s done for a set of reasons:

1. XML is very convenient to use for inter-service communication.
2. JSON is great for AJAX (web) clients. It’s perfect for GWT too.

In the recent project we’ve been using XStream for all serialization aspects and, since it can serialize both to XML and JSON, it was plugged into Jersey as a provider too. Following you can see XML and JSON providers implemented using XStream library.

XML Provider (annotated to be a default provider, it’ll be used if no Content-Type or Accept headers provided):

Adding Watermark to GWT Textbox widget

Let’s see how we can improve our UI by adding some watermarked “spice”:

Let’s define the primary style for the text box (textInput) and the dependent style for the watermark (textInput-watermark):

.textInput {
	border: 1px solid #C9C7BA;
	font-family:Tahoma, Verdana, Arial, Helvetica, sans-serif;
	font-size: 11px;
	padding-left: 2px;
	padding-top: 2px;
}

.textInput-watermark {
   /* background-image: url('images/overlay.gif');
   background-repeat: no-repeat;
   padding-left: 20px;
   vertical-align: middle; */
   font-style: italic;
   color: DarkGray;
}

Note that the watermark style can contain images as well (see the commented out piece).

After the styles were defined we need to add some code that will apply it to the text box. To do this I’m going to extend the default GWT TextBox. The trick is to hijack the OnBlur and OnFocus events. When the OnBlur is occurring, we’re going to show the watermark and OnFocus – hide it:

public class WatermarkedTextBox extends TextBox implements BlurHandler, FocusHandler
{
	String watermark;
	HandlerRegistration blurHandler;
	HandlerRegistration focusHandler;

	public WatermarkedTextBox( )
	{
		super();
		this.setStylePrimaryName("textInput");
	}

	public WatermarkedTextBox(String defaultValue)
	{
		this();
		setText(defaultValue);
	}

	public WatermarkedTextBox(String defaultValue, String watermark)
	{
		this(defaultValue);
		setWatermark(watermark);
	}

	/**
	 * Adds a watermark if the parameter is not NULL or EMPTY
	 *
	 * @param watermark
	 */
	public void setWatermark(final String watermark)
	{
		this.watermark = watermark;

		if ((watermark != null) && (watermark != ""))
		{
			blurHandler = addBlurHandler(this);
			focusHandler = addFocusHandler(this);
			EnableWatermark();
		}
		else
		{
			// Remove handlers
			blurHandler.removeHandler();
			focusHandler.removeHandler();
		}
	}

	@Override
	public void onBlur(BlurEvent event)
	{
		EnableWatermark();
	}

	void EnableWatermark()
	{
		String text = getText();
		if ((text.length() == 0) || (text.equalsIgnoreCase(watermark)))
		{
			// Show watermark
			setText(watermark);
			addStyleDependentName("watermark");
		}
	}

	@Override
	public void onFocus(FocusEvent event)
	{
		removeStyleDependentName("watermark");

		if (getText().equalsIgnoreCase(watermark))
		{
			// Hide watermark
			setText("");
		}
	}
}

Job trends for GWT and jQuery on a sharp rise

Gotta love this …

Building GWT web clients [Part 4] – How to connect GWT client to Azure web service?

Stay tuned …

Building GWT web clients [Part 3] – How to connect GWT client to JAX-RS Jersey server?

Stay tuned …

Building GWT web clients [Part 2.1] – How to control JSON output format from Jersey?

As you know that in XML you can represent the same data in variety of ways by using fields, names, attributes, etc..

The same is true to JSON. In many cases different serializers produce different JSON representation of the same objects.

JAX-RS (as well as Jersey) provide you control over what and how you want to serialize. This is accomplished via providers.

Here is an example of such provider (Note that the class should be marked with @Provider annotation):

@Provider
public class JAXBContextResolver implements ContextResolver<JAXBContext> {
    private JAXBContext context;
    private Class<?>[] types = { ListDescription.class }; 

    public JAXBContextResolver() throws Exception {
        JSONConfiguration config = JSONConfiguration.natural().build();
        context = new JSONJAXBContext(config, types);
    } 

    public JAXBContext getContext(Class<?> objectType) {
        for (Class<?> type : types) {
            if (type == objectType) {
                return context;
            }
        }
        return null;
    }
}

Note that by creating an appropriate JSONConfiguration (JSONConfiguration.natural().build()) you, in fact, control the output JSON format. The JSONConfiguration class provide 4 different JSON formatters:

1. natural (Jackson)
2. mapped
3. mappedJettison
4. Badgerfish

Here is how the output will vary, depending on the choice of the configuration. Don’t forget that the class should be annotated with A simple class (with fields (int)ID and (String)Name) added to an ArrayList and then returned back as a @GET return value:

@XmlRootElement
public class ListDescription
{
	public int ID;
	public String Name;
}

@GET
@Produces({MediaType.APPLICATION_JSON })
public List<DataListInfo> getAllLists()
{
	List<ListDescription> lists = new ArrayList<ListDescription>();
	ListDescription ls = new ListDescription();
	ls.ID = 1;
	ls.Name = "Test";
	lists.add(ls);
	return lists;
}

This is what you’ll get from each configuration (respectively):

mappedJettison:

{"listDescriptions":{"listDescription":{"ID":1,"Name":"Test"}}}

mapped:

{"listDescription":{"ID":"1","Name":"Test"}}

natural (jackson):

[{"ID":1,"Name":"Test"}]

Badgerfish:

{"listDescriptions":{"listDescription":{"ID":{"$":"1"},"Name":{"$":"Test"}}}}

Building GWT web clients [Part 2] – How to expose REST-full JAX-RS service with Jersey on Tomcat server?

In the previous article (Part 1) we’ve seen how to create a web-based REST-full client (and an appropriate server) by using GWT. GWT is not providing any “standard” REST (if you can use this word in REST context at all) interface, but, merely, exposes the server-side logic via a proprietary GWT RPC interface.

Today, the most common REST standard is the JAX-RS specification. By implementing your code along the JAX-RS guidelines you can be rest assured that you can easily switch one REST-RX library with another.

As of today there are a couple of JAX-RS libraries used by the Java community:

1. Jersey
2. Restlet
3. Portlet
4. etc…

On the other hand, being a big fan of Spring, I was hoping that Spring will provide the JAX-RS support in it’s Spring v3 release, but, looking at the M3 drop, I have realized that it’s nowhere near that promise (check my discussion on the StackOverflow).

For this post I’m going to use Jersey JAX-RS implementation. Let’s start with creating

Building fat GWT web clients [Intro] – How to create a GWT RPC client?

After months of working (mainly fighting with quirks of Java) with GWT I’ve accumulated so much knowledge on the topic so, I feel, it starts spilling over. I’m planning to convert this spill into a series of articles on how to build fat REST-full GWT web fat clients both on Java and .NET.

Here is the list of topics I’ll cover:

1. Building GWT fat client
2. Java REST-full Web services
3. .NET REST-full Web services
4. Internationalization and localization
5. IOC/DI
6. Unit testing and integration testing of all the components of the system
7. Build automation
8. and much, much more …

Here is a draft list of technologies I’ll be using:

1. GWT
2. Eclipse
3. Spring
4. Jersey
5. Tomcat
6. XStream
7. AJAX
8. JSON/XML
9. WCF
10. JUnit/TestND/NUnit
11. Selenium
12. Ant
13. TeamCity
14. and much, much more …

For starters, let’s see how to create a simple GWT fat client that talks to the REST-full Web services. As an example,

Tree event handler in GWT 1.6

The documentation was a little sparse so, if you’d like to subscribe to the click events on the tree nodes you need to add a selection handler.

This is how you add a selection handler to the whole tree:

Tree optionsTree = new Tree();
optionsTree.addSelectionHandler(new SelectionHandler()
{
    @Override
    public void onSelection(SelectionEvent event)
    {
        Window.alert(event.getSelectedItem().getText());
    }
});

Deploying GWT applications on Tomcat

If you’re looking for some guidance about deploying GWT applications on Tomcat, I found these articles helpful:

1. Deploy Google Web Toolkit(GWT) Applications using Tomcat
2. gwt-examples – tomcat6 Documentation