OSGI Service Implementation

Activator.java

package com.example.miniscout.client;

import org.eclipse.ui.plugin.AbstractUIPlugin;
import org.osgi.framework.BundleContext;

import com.example.miniscout.client.services.LocalDatabaseService;
import com.example.miniscout.shared.IDatabaseService;

public class Activator extends AbstractUIPlugin {

  private static Activator plugin;

  public void start(BundleContext context) throws Exception {
    super.start(context);
    plugin = this;
    context.registerService(IDatabaseService.class, new LocalDatabaseService(),
        null);
  }

  public void stop(BundleContext context) throws Exception {
    plugin = null;
    super.stop(context);
  }

  public static Activator getDefault() {
    return plugin;
  }

}

IDatabaseService.java

package com.example.miniscout.shared;

import java.net.URI;

public interface IDatabaseService {

  public Form load(URI source);

  public void save(Form form, URI target);
}

LocalDatabaseService.java

package com.example.miniscout.client.services;

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.net.URI;

import com.example.miniscout.shared.Form;
import com.example.miniscout.shared.IDatabaseService;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

/**
 * A Gson based database service that reads data from JSON files and converts
 * them to forms.
 */
public class LocalDatabaseService implements IDatabaseService {

  @Override
  public Form load(URI source) {
    try {
      File f = new File(source);
      FileReader r = new FileReader(f);
      Gson b = new GsonBuilder().create();
      return b.fromJson(r, Form.class);
    } catch (Exception e) {
      // swallowing just for simplicity of training...
      e.printStackTrace();
      return null;
    }
  }

  @Override
  public void save(Form form, URI target) {
    try {
      Gson b = new GsonBuilder().create();
      File f = new File(target);
      FileWriter w = new FileWriter(f);
      b.toJson(form, w);
      w.close();
    } catch (Exception e) {
      // swallowing just for simplicity of training...
      e.printStackTrace();
    }
  }
}

Services.java

package com.example.miniscout.client.services;

import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.FrameworkUtil;
import org.osgi.framework.ServiceReference;

public class Services {
  public static <T> T get(Class<T> clazz) {
		Bundle bundle = FrameworkUtil.getBundle(Services.class);
		BundleContext context = bundle.getBundleContext();
		ServiceReference<T> ref = context.getServiceReference(clazz);
		T service = context.getService(ref);
		context.ungetService(ref);
		return service;
	}
}