Advantages of rest

• Works over HTTP, known protocol with known data formats (mime types), no weird ports open in your firewall
• Every resource is uniquely identified by a URI
• Can do CRUD on those resources (they are just called POST, GET, PUT, DELETE)
• used by all the major players for cloud applications (SUN's cloudApi, Microsoft's Azure services platform)
• we might finally get rid of webdav

I'll be using the Jersey Framework for this.
As i’ve been working on a backend that will allow you to manage agile development processes (Scrum, Kanban etc) I thought I use that.

In this application every object is represented by a Card for instance a Story, Task, Bug, work Item, etc.
Cards have a hierarchical structure and can each have custom properties
The class looks something like this (removed methods for clarity):

public abstract class Card {
	private long id;
	private List<Card> children = new ArrayList<Card>();
	private List<Entry> properties = new ArrayList<Entry>()
}

and then for instance the Story class with some default values set in the constructor:

public class Story extends Card {
	public Story() {
		addProperty("Title", "A new story");
		addProperty("Description", "as a .. I want .. for the benefit of ..");
		addProperty("Storypoints", "0");
	}
}

To be able to return these objects through REST they need to be in a format that can be distributed over HTTP, in this case we will be using XML and JSON.
The Java XML Bindings are perfectly suited to create xml representations of our classes

@XmlRootElement(name="card")
public abstract class Card {
	private long id;
 
	@XmlAttribute(name="type")
	protected String instance = this.getClass().getSimpleName();
 
	@XmlElement(name="card")
	private List<Card> children = new ArrayList<Card>();
 
	@XmlElement(name="property")
	private List<Entry> properties = new ArrayList<Entry>();
 
	@XmlAttribute
	public long getId() {}
}

* the Entry class is a simple class with a name and value property, I choose this approach as JAXB has an issue in representing HashMaps() in XML
this will produce the following xml

<card id="4" type="Task">
	<property value="nobody" name="assigned"/>
	<property value="Slay dragon" name="Title"/>
	<property value="his weak spot seems to be a small spot on his belly" name="Description"/>
	<property value="4" name="hours"/>
</card>

for JSON we don’t need to do anything special then include the jersey-json.jar to the project.

Now to configure and hookup the rest servlet
I added the jersey servlet to my web.xml

<servlet>  
    	<servlet-name>Rest Web Service</servlet-name>  
    	<servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>  
    	<load-on-startup>1</load-on-startup>  
</servlet>  
<servlet-mapping>  
    	<servlet-name>Rest Web Service</servlet-name>  
    	<url-pattern>/services/*</url-pattern>  
</servlet-mapping>

And create the service provider class

@PerRequest
@Path("/agileassistant")
@Consumes({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
@Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
public class AgileAssistantService {
 ...
}

This will tell Jersey that this is a provider that will respond to requests to /rest/agileassistant, accept JSON and XML and can output JSON or XML depending on the accept headers sent by the client

Now if we for instance want to return the first card (rootCard) and all its children we add this method

	public static Card rootCard = Card.createCard(Root.class);
 
	@GET
	public Card getRoot() {
		return rootCard;
	}

(in my data model the rootCard is always present and functions as a starting point to add the rest of the cards in a hierarchical structure)
So requesting this card will effectively return the entire structure for my test data:

 
<card id="1" type="Root">
	<card id="2" type="Story">
		<property value="Convince King" name="Title"/>
		<property value="to let the prince go on an adventure" name="Description"/>
		<property value="5" name="Storypoints"/></card>
	<card id="3" type="Story">
		<card id="4" type="Task">
			<property value="nobody" name="assigned"/>
			<property value="Slay dragon" name="Title"/>
			<property value="his weak spot seems to be a small spot on his belly" name="Description"/>
			<property value="4" name="hours"/>
		</card>
		<card id="5" type="Task">
			<property value="nobody" name="assigned"/>
			<property value="Rescue Princess" name="Title"/>
			<property value="She'll be the one screaming from the tower window" name="Description"/>
			<property value="2" name="hours"/>
		</card>
		<property value="Once upon a time" name="Title"/>
		<property value="in a land far far away" name="Description"/>
		<property value="5" name="Storypoints"/>
	</card>
</card>

Doing a parameterized query is almost as easy

	@GET
	@Path("/card/{id}")
	public Card getCard(@PathParam("id") long id) {
		return getCardById(rootCard, id);
	}

here the id that you specify will be injected into the parameter
giving the following output

<card id="4" type="Task">
	<property value="nobody" name="assigned"/>
	<property value="Slay dragon" name="Title"/>
	<property value="his weak spot seems to be a small spot on his belly" name="Description"/>
	<property value="4" name="hours"/>
</card>

To conclude enabling rest for your applications is pretty easy, writing this blog took longer than writing the code.
In a next post I will add POST/PUT/DELETE requests to store data in your application

var someObject : bind myJavaclass.getProperty();

JavaFX needs to be aware of any changes to the bound variables to be able to update the related objects. It does this automagically for all javafx objects.
It seems JavaFX uses the Observer/Observable pattern for all its internal objects, well we can do the same to bind with JavaObjects.
To get myself familiar with JavaFX i decided to write a photoviewer/editor. This application has a java backend with in particular a Photo class which contains all the information of a certain picture, filename, path, tags, exif information etcetera

To get changes in the Java class to appear in the gui I create a PhotoAdapter javafx class that extends Observer and implemented the properties I need in my GUI.

public class PhotoAdapter extends Observer {
    public-read var filename: String;
    public-read var tags: String[];
    public-read var exif: String[];
 
    public-init var photo: Photo
         on replace {
            photo.addObserver(this);
            filename=photo.getFilename();
            tags = photo.getTags();
            exif = photo.getExif();
         };
 
    override function update(observable: Observable, arg: Object) {
        filename = photo.getFilename();
        tags = photo.getTags();
        exif = photo.getExif();
    }

after that I had my existing Java Photo class extend Observable and in every method that made changes I added the methods setChanged() and NotifyObservers() to inform the Observers about the change

public class Photo extends Observable {
    private Map<String, String> exifInformation; 
    ....
    public void setExifInformation(Map exifInfo) {
        this.exifInformation = exifInfo;
        setChanged();
        notifyObservers();
    }
}

in my main javafx class I can then use it as follows

    var photoAdapter = PhotoAdapter {
        photo : new Photo(startImage);
}

and use to fill a ListView swing object with for instance the tags:

    ListView {
        items:     bind photoAdapter.tags;
        width:     200;
        height:    300;
    }

et viola, thats all that there is to it

In .Net an object that implements the IDisposable interface can be initiated with the Using command like this:

using (TextWriter w = File.CreateText("log.txt"))
    { w.WriteLine("This is line one");
}

After the block has executed, using will take care of closing the writer and freeing the resources.
This gives me solid readable code without memoryleaks.

Now looking at Java, closing resources usually involves putting a close() in a finally block, with another try-catch construction to catch exceptions that the close() can throw.
this is ugly, errorprone and can obfuscate the real exception that happened.

Java 7 comes to the rescue, one of the approved proposals for java 7 is "automatic resource management"
the following code block will demonstrate this

static void copy(String src, String dest) throws IOException {
   try (InputStream in = new FileInputStream(src); 
         OutputStream out = new FileOutputStream(dest)) {
 
        byte[] buf = new byte[8192];
        int n;
        while ((n = in.read(buf)) >= 0)
        out.write(buf, 0, n);
    }
    //optional catch block
    //optional finally block
}

In Java 6 or lower the above code would contain 2 try-finally blocks to handle closing the input and ouput streams, another 2 try-catch blocks to handle exceptions from the close() commands, and more catches for exceptions you would want to handle specifically

Off all the features in java 7 this is the one I'm looking forward the most, the forkjoin and invokeDynamic changes following close though.
here is a list of all the features in java 7
http://openjdk.java.net/projects/jdk7/features/ ]]> http://blog.addictivesoftware.net/2009/11/nets-using-for-java/feed/ 0