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From neykov <...@git.apache.org>
Subject [GitHub] brooklyn-server pull request: Service loader updates
Date Thu, 17 Mar 2016 17:00:59 GMT
Github user neykov commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/65#discussion_r56539375
  
    --- Diff: api/src/main/java/org/apache/brooklyn/api/framework/FrameworkLookup.java ---
    @@ -0,0 +1,179 @@
    +/*
    + * 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 org.apache.brooklyn.api.framework;
    +
    +import org.apache.brooklyn.util.guava.Maybe;
    +import org.apache.brooklyn.util.osgi.OsgiUtil;
    +import org.osgi.framework.*;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +import java.util.ArrayList;
    +import java.util.Collection;
    +import java.util.List;
    +import java.util.ServiceLoader;
    +
    +/**
    + * A utility to fetch an instance of a class from either OSGI if available, or by a Service
Loader otherwise.
    + *
    + * The intention of this class is to provide a means to lookup beans in the OSGI service
registry that were
    + * previously looked up via a ServiceLoader, but still maintain the backward compatible
behaviour when not running
    + * in an OSGI container.
    + *
    + * NOTE, when OSGI bundle registry is used, this code performs a BundleContext.getService().
When calling
    + * BundleContext.getService() the reference count for the service in question is increased,
and without any calls to
    + * BundleContext.ungetService() the only moment it will drop to zero is when the client
bundle is unloaded,
    + * which this code does not do.  Therefore this class is not suitable for use in a situation
where client code needs
    + * to take account of services coming and going, and explicitly avoid using the service
when its reference count has
    + * gone to zero.
    + */
    +public class FrameworkLookup {
    +
    +    private static final Logger LOG = LoggerFactory.getLogger(FrameworkLookup.class);
    +
    +    /**
    +     * Find an instance of the given class in the framework.
    +     * This first performs an OSGI lookup if the OSGI framework is available. If it is
not then it falls back to
    +     * attempting a lookup from the current context classpath via a ServiceLoader.
    +     *
    +     * @param clazz The class (typically the class of an interface) to search in the
framework.
    +     * @param <T>  The type for the class.
    +     * @return  A maybe of the instance found in the framework.
    +     */
    +    public static <T> Maybe<T> lookup (Class<T> clazz) {
    +        return lookup(clazz, null);
    +    }
    +
    +    /**
    +     * Find an instance of the given class in the framework.
    +     * This first performs an OSGI lookup if the OSGI framework is available. If it is
not then it falls back to
    +     * attempting a lookup from the current context classpath via a ServiceLoader.
    +     *
    +     * @param clazz The class (typically the class of an interface) to search in the
framework.
    +     * @param loader If falling back to ServiceLoader, this class loader is used to load
the class. If <tt>null</tt>,
    +     *         the system class loader (or, failing that, the bootstrap class loader)
is used.
    +     * @param <T>  The type for the class.
    +     * @return  A maybe of the instance found in the framework.
    +     */
    +    public static <T> Maybe<T> lookup (Class<T> clazz, ClassLoader
loader) {
    --- End diff --
    
    Personal preference, could cut this file in half if supporting only the `lookupAll` case
with users getting the first entry where needed.


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