On the server-side, I use
com.google.gson.*
On the client-side, I use
com.google.gwt.core.client.JavaScriptObject;
com.google.gwt.json.client.*;
There are two modes to using these APIs.
- Use GWT RPC to send Java structures back and forth.
In this mode, you are blind to JSON and never need to even refer to
any JSON API.
- Send JSON explicitly and therefore having to be aware of JSON APIs
on both client and server side.
What concerns you is the second mode.
For example, I am writing a framework which inspects the DAO on the
server-side to construct the JSON representing those structures. The
GWT client reads the server's JSON representation and data and builds
the GWT (or SmartGWT) Ui dynamically and fill them up with data
spontaneously.
On the server-side, using com.google.gson.*, for example,
final JsonObject schema = new JsonObject(); // construct the schema
root as hash node.
schema.addProperty("name", name); // add key-string value pairs
JsonArray elements = new JsonArray(); // create a JSON array
schema.add("elements", elements); // add key-child node pairs to hash
node.
JsonObject elem = new JsonObject();
elements.add(elem); // json obj to jsonarray.
Gson gson = new GsonBuilder()
.setPrettyPrinting().create();
gson.toJson(schema); // print the JSON representation to output.
On client-side, read this article
http://code.google.com/webtoolkit/articles/using_gwt_for_json_mashups.html.
And then you could use my library by extending
JsonRemoteScriptCall.java at
http://code.google.com/p/synthfuljava/source/browse/#svn/trunk/gwt/jsElements/org/synthful/gwt/javascript/client.
This library works on the premise of jsonp. The principle is, you
modify your server-side JSON provider to do envelope the JSON
structure as executable javascript:
var jsdata = {
// json structure
}
eatJson(jsdata);
On client-side:
import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.json.client.*;
JsonRemoteScriptCall myJRSC = new JsonRemoteScriptCall() {
extends JsonRemoteScriptCall {
@Override
public void onJsonRSCResponse(JavaScriptObject jso) {
if (jso==null) return;
this.ignite();
JSONObject json = new JSONObject(jso);
// traverse your json tree here.
}
}
What you need to take note is how to trigger reading in the JSON:
myJRSC.call( url of json data source, "eatJson");
Notice that the callback onJsonRSCResponse is mapped to eatJson by
this utility, so that at the end of the json file, eatJson is executed
as a javascript call which actually runs the callback
onJsonRSCResponse.
Take note that on the client-side use of com.google.gwt.json.client.*
APIs, you have to be quite explicit in testing if a node is another
node, is an array, is a string, etc:
static public String getStringValue(JSONObject json, String key){
if (json == null || key == null )
return null;
JSONValue typejsv = json.get(key);
if (typejsv!=null){
JSONString typestr = typejsv.isString();
if (typestr!=null)
return typestr.stringValue();
}
return null;
}
static public JSONArray getJSONArray(JSONObject json, String key){
if (json == null || key == null )
return null;
JSONValue jsv = json.get(key);
if (jsv!=null){
return jsv.isArray();
}
return null;
}
static public JSONObject getJSONObject(JSONObject json, String key){
if (json == null || key == null )
return null;
JSONValue jsv = json.get(key);
if (jsv!=null){
return jsv.isObject();
}
return null;
}
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