CalculatorServiceImpl.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package calculator.dosgi.impl;

import static org.osgi.framework.Constants.OBJECTCLASS;

import java.util.HashMap;
import java.util.Map;

import org.osgi.framework.BundleContext;
import org.osgi.framework.Filter;
import org.osgi.framework.InvalidSyntaxException;
import org.osgi.util.tracker.ServiceTracker;

import calculator.dosgi.CalculatorService;
import calculator.dosgi.operations.AddService;
import calculator.dosgi.operations.DivideService;
import calculator.dosgi.operations.MultiplyService;
import calculator.dosgi.operations.SubtractService;

/**
 * An implementation of the Calculator service.
 */
public class CalculatorServiceImpl implements CalculatorService {
    private Map<Class<?>, ServiceTracker> remoteServices = new HashMap<Class<?>, ServiceTracker>();

    public CalculatorServiceImpl() {
        super();
    }

    public CalculatorServiceImpl(BundleContext context) {
        super();
        for (Class<?> cls : new Class<?>[] {AddService.class, SubtractService.class, MultiplyService.class,
                                            DivideService.class}) {
            Filter remoteFilter = null;
            try {
                remoteFilter =
                    context.createFilter("(&(" + OBJECTCLASS + "=" + cls.getName() + ") (service.imported=*))");
            } catch (InvalidSyntaxException e) {
                e.printStackTrace();
            }
            ServiceTracker tracker = new ServiceTracker(context, remoteFilter, null);
            this.remoteServices.put(cls, tracker);
            tracker.open();
        }
    }

    private <T> T getService(Class<T> cls) {
        ServiceTracker tracker = remoteServices.get(cls);
        try {
            // Wait for 10 seconds until the remote services are imported
            tracker.waitForService(10000);
        } catch (InterruptedException e) {
            throw new IllegalStateException(cls.getSimpleName() + " is not available");
        }
        Object[] remoteObjects = tracker.getServices();
        if (remoteObjects != null) {
            for (Object s : remoteObjects) {
                if (cls.isInstance(s)) {
                    System.out.println("Remote service: " + s);
                    return cls.cast(s);
                }
            }
        }
        throw new IllegalStateException(cls.getSimpleName() + " is not available");
    }

    public double add(double n1, double n2) {
        return getService(AddService.class).add(n1, n2);
    }

    public double subtract(double n1, double n2) {
        return getService(SubtractService.class).subtract(n1, n2);
    }

    public double multiply(double n1, double n2) {
        return getService(MultiplyService.class).multiply(n1, n2);
    }

    public double divide(double n1, double n2) {
        return getService(DivideService.class).divide(n1, n2);
    }
}