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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