Proof of Concept: GWT, Restlet, OSGi and Maven
After some difficulties I got a project working, which consists of a simple GWT application with a Restlet backend. The application consists of four OSGi bundles, which work inside eclipse PDE. Also, all of these modules and their dependencies are declared using Maven 2.
Overview:
The user interface is based on google‘s standard project from the google eclipse plugin.
The button Ping triggers a very simple REST call to the server (based on example from Restlet documentation)
tstBtn.addClickHandler(new ClickHandler() {
@Override public void onClick(ClickEvent event) { ClientResource r = new ClientResource("/ping");
r.setOnResponse(new Uniform() { public void handle(Request request, Response response) { try { tstBtn.setText(response.getEntity().getText()); } catch (IOException e) { e.printStackTrace(); } } }); r.get(); } });
Clicking this button should result in the caption of the button being filled with a response from the server.
The server resource is as following:
public class PingResource extends ServerResource {
@Get("txt") public String toText() { StringBuilder sb = new StringBuilder("Restlet server alive. Method: "); sb.append(getRequest().getMethod());
ChallengeResponse challengeResponse = getRequest() .getChallengeResponse(); if (challengeResponse != null) { sb.append("/ Auth. scheme: "); sb.append(challengeResponse.getScheme()); }
return sb.toString(); } }
The send button should work in the same way as in the google example; only that the remote procedure call is facilitated using Restlet.
GWT Client:
GreetingServiceAsync r = GWT.create(GreetingServiceAsync.class); r.getClientResource().setReference("/services/greet"); r.getClientResource().getClientInfo().getAcceptedMediaTypes().add(new Preference(MediaType.APPLICATION_JAVA_OBJECT_GWT)); r.greetServer(new Name(nameField.getText()), new AsyncCallback() {
@Override public void onFailure(Throwable caught) { // Show the RPC error message to the user dialogBox .setText("Remote Procedure Call - Failure"); serverResponseLabel .addStyleName("serverResponseLabelError"); serverResponseLabel.setHTML(SERVER_ERROR+"
"+caught.getMessage()); dialogBox.center(); closeButton.setFocus(true); }
@Override public void onSuccess(String result) { dialogBox.setText("Remote Procedure Call"); serverResponseLabel .removeStyleName("serverResponseLabelError"); serverResponseLabel.setHTML(result); dialogBox.center(); closeButton.setFocus(true); } });
Restlet Server:
public class GreetingServiceServerResource extends ServerResource implements GreetingService { @Override public Representation handle() { CompositeClassLoader customCL = new CompositeClassLoader(); customCL.addClassLoader(Thread.currentThread().getContextClassLoader()); customCL.addClassLoader(Name.class.getClassLoader()); ClassLoader oldCL = Thread.currentThread().getContextClassLoader(); Thread.currentThread().setContextClassLoader(customCL); Representation rep = super.handle(); Thread.currentThread().setContextClassLoader(oldCL); return rep; } @Override @Post public String greetServer(Name name) throws IllegalArgumentException { System.out.println(“Name submitted: “+name.name); return “Welcome “+name.name+” from Restlet!”; }
}
OSGi Bundles:
Under equinox, the following modules were required:
id State Bundle 0 ACTIVE org.eclipse.osgi_3.5.2.R35x_v20100126 Fragments=2, 3 2 RESOLVED org.eclipse.persistence.jpa.equinox.weaving_1.1.3.v20091002-r5404 Master=0 3 RESOLVED javax.transaction_1.1.1.v201002111330 Master=0 17 ACTIVE org.hamcrest.core_1.1.0.v20090501071000 18 ACTIVE thrdGWTUser_0.0.2.SNAPSHOT 19 ACTIVE javax.servlet_2.5.0.v200806031605 21 ACTIVE org.junit4_4.5.0.v20090824 41 ACTIVE org.eclipse.osgi.services_3.2.0.v20090520-1800 49 ACTIVE thrdRestletGWT_0.0.2 50 ACTIVE thrdRestletExtSimple_0.0.2 51 ACTIVE zzSampleGWTClient_0.0.2 52 ACTIVE zzSampleRestletServer_0.0.2
Lessons Learned and Helpful Resources
- org.restlet.ext.simpleframework is deprecated and should not be used - the current version for the Maven GWT plugin is 1.3-SNAPSHOT or 1.3.1.google. My projects worked with 1.3-SNAPSHOTS at the end. - Restlet might have problems with transporting String objects. Therefore I encapsulated the String with the username in a Name object. - Classloaders: GWT RPC, OSGi and Restlet - GWT Module XXX not found in project sources or resources. - CLAP Protocol in Restlet and OSGi - GWT + OSGi + Maven - Restlet Server: OSGi and Maven - Deployment of GWT Applications (Part 2) - Maven, GWT and Eclipse Quick start (Part 1)
