1 files changed, 72 insertions, 0 deletions
diff --git a/java/broker/src/main/java/org/apache/qpid/server/plugin/QpidServiceLoader.java b/java/broker/src/main/java/org/apache/qpid/server/plugin/QpidServiceLoader.java
new file mode 100644
index 0000000000..a0e0346ce0
--- /dev/null
+++ b/java/broker/src/main/java/org/apache/qpid/server/plugin/QpidServiceLoader.java
@@ -0,0 +1,72 @@
+/*
+ * 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.qpid.server.plugin;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ServiceLoader;
+
+import org.apache.log4j.Logger;
+
+/**
+ * Simple facade over a {@link ServiceLoader} to instantiate all configured implementations of an interface.
+ */
+public class QpidServiceLoader<C>
+{
+    private static final Logger _logger = Logger.getLogger(QpidServiceLoader.class);
+
+    public Iterable<C> instancesOf(Class<C> clazz)
+    {
+        return instancesOf(clazz, false);
+    }
+
+    /**
+     * @throws RuntimeException if at least one implementation is not found.
+     */
+    public Iterable<C> atLeastOneInstanceOf(Class<C> clazz)
+    {
+        return instancesOf(clazz, true);
+    }
+
+    private Iterable<C> instancesOf(Class<C> clazz, boolean atLeastOne)
+    {
+        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+        Iterator<C> serviceLoaderIterator = ServiceLoader.load(clazz, classLoader).iterator();
+
+        // create a new list so we can log the count
+        List<C> serviceImplementations = new ArrayList<C>();
+        while(serviceLoaderIterator.hasNext())
+        {
+            serviceImplementations.add(serviceLoaderIterator.next());
+        }
+
+        if(atLeastOne && serviceImplementations.isEmpty())
+        {
+            throw new RuntimeException("At least one implementation of " + clazz + " expected");
+        }
+
+        if(_logger.isDebugEnabled())
+        {
+            _logger.debug("Found " + serviceImplementations.size() + " implementations of " + clazz);
+        }
+
+        return serviceImplementations;
+    }
+}