1 files changed, 117 insertions, 0 deletions
diff --git a/policy-utils/src/main/java/org/openecomp/policy/drools/utils/OrderedServiceImpl.java b/policy-utils/src/main/java/org/openecomp/policy/drools/utils/OrderedServiceImpl.java
new file mode 100644
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+++ b/policy-utils/src/main/java/org/openecomp/policy/drools/utils/OrderedServiceImpl.java
@@ -0,0 +1,117 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * policy-utils
+ * ================================================================================
+ * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * Licensed 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.openecomp.policy.drools.utils;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.ServiceLoader;
+
+/**
+ * This class is a template for building a sorted list of service instances,
+ * which are discovered and created using 'ServiceLoader'. 
+ */
+public class OrderedServiceImpl<T extends OrderedService>
+{
+  // sorted list of instances implementing the service
+  private List<T> implementers = null;
+
+  // 'ServiceLoader' that is used to discover and create the services
+  private ServiceLoader<T> serviceLoader = null; //ServiceLoader.load(T.class);
+
+  /**
+   * Constructor - create the 'ServiceLoader' instance
+   *
+   * @param clazz the class object associated with 'T' (I supposed it could
+   *	be a subclass, but I'm not sure this is useful)
+   */
+  public OrderedServiceImpl(Class clazz)
+  {
+	// This constructor wouldn't be needed if 'T.class' was legal
+	serviceLoader = ServiceLoader.load(clazz);
+  }
+
+  /**
+   * @return the sorted list of services implementing interface 'T' discovered
+   *	by 'ServiceLoader'.
+   */
+  public synchronized List<T> getList()
+  {
+	if (implementers == null)
+	  {
+		rebuildList();
+	  }
+	return(implementers);
+  }
+
+  /**
+   * This method is called by 'getList', but could also be called directly if
+   * we were running with a 'ClassLoader' that supported the dynamic addition
+   * of JAR files. In this case, it could be invoked in order to discover any
+   * new services implementing interface 'T'. This is probably a relatively
+   * expensive operation in terms of CPU and elapsed time, so it is best if it
+   * isn't invoked too frequently.
+   *
+   * @return the sorted list of services implementing interface 'T' discovered
+   *	by 'ServiceLoader'.
+   */
+  public synchronized List<T> rebuildList()
+  {
+	// build a list of all of the current implementors
+	List<T> tmp = new LinkedList<T>();
+	for (T service : serviceLoader)
+	  {
+		tmp.add(service);
+	  }
+
+	// Sort the list according to sequence number, and then alphabetically
+	// according to full class name.
+	Collections.sort(tmp, new Comparator<T>()
+					 {
+					   public int compare(T o1, T o2)
+						 {
+						   int s1 = o1.getSequenceNumber();
+						   int s2 = o2.getSequenceNumber();
+						   int rval;
+						   if (s1 < s2)
+							 {
+							   rval = -1;
+							 }
+						   else if (s1 > s2)
+							 {
+							   rval = 1;
+							 }
+						   else
+							 {
+							   rval = o1.getClass().getName().compareTo
+								 (o2.getClass().getName());
+							 }
+						   return(rval);
+						 }
+					 });
+
+	// create an unmodifiable version of this list
+	implementers = Collections.unmodifiableList(tmp);
+	System.out.println("***** OrderedServiceImpl implementers:\n" + implementers);
+	return(implementers);
+  }
+}