Service Plugins

Web services are one of the most flexible ways of expanding Dicoogle with new features. Currently, there are two ways to achieve this:

• Jetty Servlets can be created and registered using a plugin of type JettyPluginInterface. Create your own servlets (see HttpServlet), then attach them into a handler list in getJettyHandlers:

• Rest Service plugins consider a subset of the Restlet framework API, allowing developers to create and attach simple server resources. Their integration is simpler, although more brittle. A proposal for better Restlet support is currently in review. In the mean time, server resources can be implemented and integrated by creating a new ServerResource like this:

Jetty Servlets

The servlet API is a versatile means of creating services in Java server applications.

A servlet class should inherit from the HttpServlet class. It may then override one or more of the HTTP request method handlers (doGet, doPost, doPut, and so on).

public class MyWebServlet  extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response)
                    throws ServletException, IOException {

        String name = req.getParameter("name");
        response.setContentType("application/json");
        JSONObject o = new JSONObject();
        o.put("name", name);
        response.getWriter().print(o.toString());
    }
}

Through the JettyPluginInterface, a list of Jetty server handlers (HandlerList) is passed to the core system, to be attached to the main Dicoogle web server. Below is a possible implementation of the getJettyHandlers() method:

@Override
public HandlerList getJettyHandlers() {

    // encapsulate servlets into holders, then add them to handlers.
    ServletContextHandler handler = new ServletContextHandler();
    handler.setContextPath("/sample");
    handler.addServlet(new ServletHolder(this.myWebService), "/hello");

    // add all handlers to a handler list and return it
    HandlerList l = new HandlerList();
    l.addHandler(handler);

    return l;
}

An instance of this class must be created, preferably in the plugin set constructor. Then, it must be registered into the platform by returning the plugin via the PluginSet#getJettyPlugins method.

RESTlet services

The RESTlet API is a bit more straightforward and simple, albeit more limited in some cases. The REST services implemented are directly described by method prototypes and annotations instead of a fixed set of methods. Dicoogle enables the attachment of RESTlet server resources. See an example below.

public class RSIWebResource extends ServerResource {
    
    @Get
    public Representation test() {
        StringRepresentation sr = new StringRepresentation("{\"name\":\"hello\"}");
        sr.setMediaType(MediaType.APPLICATION_JSON);
        return sr;
    }
    
    // You can handle all CRUD operations. More information in the Restlet documentation.
    
    // `toString` defines the service endpoint.
    @Override
    public String toString() {
        return "service/endpoint/test";
    }
}

Likewise, an instance of this class must be created and registered through the PluginSet#getRestPlugins method.