Add the JAR to your project's build path

Download the Itemscript distribution archive, extract it, and copy the JAR itemscript-gwt-x.x.x.jar into your project, and add it to your build path.

Add the Itemscript module to your GWT module config

In your module's .gwt.xml configuration file, add the following line above your module's entry-point:

<inherits name="org.itemscript.Itemscript" />

This will allow you to use the Itemscript classes, and the entry-point for the Itemscript module will create a single static JsonSystem instance at GwtSystem.SYSTEM. Because the GWT environment is single-threaded, you probably don't need to create any new instances of JsonSystem, although if you need to, you can do so like this:

    JsonSystem system = new ItemscriptSystem(new GwtConfig());

Create and populate a JsonObject

    JsonSystem system = GwtSystem.SYSTEM;
    JsonObject object = system.createObject();
    object.put("abc", "xyz");
    object.put("def", 123);
    object.put("ghi", true);
    JsonArray array = object.createArray("jkl");
    array.add("one");
    array.add(2);
    array.add(true);

Convert a JsonObject to a JSON string

    String json = object.toString();
    System.out.println(json);

prints:

{
    "jkl" : [
        "one",
        2,
        true
    ],
    "abc" : "xyz",
    "ghi" : true,
    "def" : 123
}

Parse a JSON string

    String json2 = "{\"foo\" : \"bar\"}";
    JsonObject object2 = system.parse(json2).asObject();
    String fooValue = object2.getString("foo");
    System.out.println(fooValue); // prints "bar"

Parse a JSON value loaded via HTTP

Note that in the GWT environment, you don't want to wait until a value loaded from HTTP is fully loaded before continuing execution. So, you need to supply a callback that will be invoked when the get operation completes.

    system.get("http://itemscript.org/test.json", new GetCallback() {
        @Override
        public void onSuccess(JsonValue value) {
            System.out.println(value);
        }

        @Override
        public void onError(Throwable e) {
            System.err.println("error: " + e);
        }
    });

prints:

{
    "test-boolean" : true,
    "test-object" : {
        "abc" : "def",
        "foo" : [
            "x",
            "y",
            "z"
        ]
    },
    "test-int" : 1,
    "test-null" : null,
    "test-string" : "value",
    "test-array" : [
        "one",
        "two",
        "three",
        true,
        1,
        null,
        1.5,
        {
            "xyz" : "123"
        }
    ],
    "test-float" : 1.5
}

PUT a value via HTTP

 GwtSystem.SYSTEM.put("/path/to/value", value, new PutCallback() {
                    @Override
                    public void onError(Throwable e) {
                        throw new RuntimeException(e);
                    }

                    @Override
                    public void onSuccess(PutResponse putResponse) {
                        System.err.println("put complete");
                    }
                });

POST a value via HTTP

Support for PUT is unfortunately not universal in older browsers. You can force a request to be a POST request by adding a query string, which the server should ignore.

This mechanism is probably going to change; a general way of detecting whether the browser supports PUT and DELETE and a standard encapsulation of PUT and DELETE requests in POST requests would be more useful, or just a flag that switches everything to PUT-in-POST/DELETE-in-POST.

 GwtSystem.SYSTEM.put("/path/to/value?post", value, new PutCallback() {
                    @Override
                    public void onError(Throwable e) {
                        throw new RuntimeException(e);
                    }

                    @Override
                    public void onSuccess(PutResponse putResponse) {
                        RootPanel.get()
                                .add(new HTML(StaticJsonUtil.toHtmlJson(putResponse.value())));
                    }
                });

Itemscript is a registered trademark of Data Base Architects, Inc. The Itemscript specification, the Itemstore API specification and the JAM template language specification are open source works published under the new BSD license.