GWT cross-domain rpc - gwt-rpc

Question

I need to call a GWT application service from javascript which is running on different domain.
How could this be done? How do I point from my applicaton to the javascript url?
Thank you.

Answer 1

The idea behind a cross domain request is the your java script creats a script tag which loads a generated java script from the forgein url. When loaded the generated java script is evaluated and calls a callback function you created.
The following code ist not testet and shows the idea:
public class CrossSiteDomainRequest {
/** Counter to create unique ids for callback function. */
private static int idCounter = 0;
/** Url to load the javascript from. */
private String url;
/**
* Creates a new loader with the given <code>url</code>.
* #param url to load the java script from {#link #url}.
*/
public CrossSiteDomainRequest(String url) {
this.url = url;
}
/**
* Uses the {#link #url} to load the data from another url.
*/
public void load() {
String callbackId = "callbackId" + idCounter++;
String prepend = url.indexOf("?") != -1 ? "&" : "?";
String u = url + prepend + "callback=" + callbackId// Add more Parameters
createCallback(this, transId);
Element script = DOM.createElement("script");
script.setAttribute("src", u);
script.setAttribute("id", callbackId);
script.setAttribute("type", "text/javascript");
script.setAttribute("language", "JavaScript");
getHead().appendChild(script);
}
/**
* Destroys the callback with the given <code>id</code>.
* #param id of the script tag and native javascript callback function which should be destroyed.
*/
protected void destroyCallbackmethod(String id) {
getHead().removeChild(DOM.getElementById(id));
removeCallback(id);
}
/**
* This method is invoked by the callback to handel the loaded data.
* #param callbackId DOM-Id of the callback whick invoked this method.
* #param jso Object that encapsultes the loaded data.
*/
#SuppressWarnings("unchecked")
protected void onReceivedData(String callbackId, JavaScriptObject jso) {
try {
// Read data
} catch (Exception e) {
// Handle Error
}
destroyCallbackmethod(callbackId);
}
/**
* Creates a native javascript callback.
* #param cscr to invoke the {#link #onReceivedData(String, com.google.gwt.core.client.JavaScriptObject)} on when the data has been loaded.
* #param callbackId DOM-Id to create the callback back.
*/
private native void createCallback(CrossSiteDomainRequest cscr, String callbackId) /*-{
$wnd[callbackId] = function(j) {
proxy.#com.test.package.client.CrossSiteDomainRequest::onReceivedData(Ljava/lang/String;Lcom/google/gwt/core/client/JavaScriptObject;)(callbackId, j);
};
}-*/;
private native void removeCallback(String callbackId) /*-{
$wnd[callbackId] = null;
}-*/;
public static native Element getHead() /*-{
return $doc.getElementsByTagName('head')[0];
}-*/;
}
If you create a CrossSiteDomainRequest Object for the URL http://www.test.com/loadXDR.js
you have to evaluate the callbackId parameter and generate a java script which may looks like this:
callbackId({"menu": {
"id": "file",
"value": "File",
"popup": {
"menuitem": [
{"value": "New", "onclick": "CreateNewDoc()"},
{"value": "Open", "onclick": "OpenDoc()"},
{"value": "Close", "onclick": "CloseDoc()"}
]
}
}});
The callbackId has to be replaced accordingly.