Add Network Logging Feature

This is part 1 of introducing the mdc filter feature. Network
logging has to have interception points in order to pre/post
process messages coming in from a network endpoint.

The OrderedService interface and OrderedServiceImpl of the
drools-pdp project have now been migrated to common but is
also left in drools-pdp to mitigate disruption to existing
features. However for features that need to use common's
OrderedServiceImpl and drools-pdp version of OrderedServiceImpl
there will be a conflict with getSequenceNumber(). So a migration
of the other features is suggested.

Network logging is moved to its own util class so that feature
hooks can be invoked any time an event is being logged by a
network logger. This util class will also be accessible to
drools-applications in the case where drools-applications
would like to invoke network logging features for REST events.

Change-Id: I83d7c46e5abb351486f841c3be4d9009f7992476
Issue-ID: POLICY-1499
Signed-off-by: Daniel Cruz <dc443y@att.com>

1 files changed, 135 insertions, 0 deletions

diff --git a/utils/src/main/java/org/onap/policy/common/utils/services/OrderedServiceImpl.java b/utils/src/main/java/org/onap/policy/common/utils/services/OrderedServiceImpl.java
new file mode 100644
index 00000000..bbd30220
--- /dev/null
+++ b/utils/src/main/java/org/onap/policy/common/utils/services/OrderedServiceImpl.java
@@ -0,0 +1,135 @@
+/*
+ * ============LICENSE_START=======================================================
+ * utils
+ * ================================================================================
+ * Copyright (C) 2019 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.onap.policy.common.utils.services;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.ServiceLoader;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * 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> {
+    // logger
+    private static Logger  logger = LoggerFactory.getLogger(OrderedServiceImpl.class); 
+
+    // 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;
+
+    // use this to ensure that we only use one unique instance of each class
+    @SuppressWarnings("rawtypes")
+    private static HashMap<Class,OrderedService> classToSingleton = new HashMap<>();
+
+    /**
+     * 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<T> clazz) {
+        // This constructor wouldn't be needed if 'T.class' was legal
+        serviceLoader = ServiceLoader.load(clazz);
+    }
+
+    /**
+     * Get List of implementers.
+     * 
+     * @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'.
+     */
+    @SuppressWarnings("unchecked")
+    public synchronized List<T> rebuildList() {
+        // build a list of all of the current implementors
+        List<T> tmp = new LinkedList<>();
+        for (T service : serviceLoader) {
+            tmp.add((T)getSingleton(service));
+        }
+
+        // Sort the list according to sequence number, and then alphabetically
+        // according to full class name.
+        Collections.sort(tmp, (o1, o2) -> {
+            int s1 = o1.getSequenceNumber();
+            int s2 = o2.getSequenceNumber();
+            if (s1 < s2) {
+                return -1;
+            } else if (s1 > s2) {
+                return 1;
+            } else {
+                return o1.getClass().getName().compareTo(o2.getClass().getName());
+            }
+        });
+
+        // create an unmodifiable version of this list
+        implementers = Collections.unmodifiableList(tmp);
+        logger.info("***** OrderedServiceImpl implementers:\n {}", implementers);
+        return implementers;
+    }
+
+    /**
+     * If a service implements multiple APIs managed by 'ServiceLoader', a
+     * separate instance is created for each API. This method ensures that
+     * the first instance is used in all of the lists.
+     *
+     * @param service this is the object created by ServiceLoader
+     * @return the object to use in place of 'service'. If 'service' is the first
+     *     object of this class created by ServiceLoader, it is returned. If not,
+     *     the object of this class that was initially created is returned
+     *     instead.
+     */
+    private static synchronized OrderedService getSingleton(OrderedService service) {
+        // see if we already have an instance of this class
+        OrderedService rval = classToSingleton.get(service.getClass());
+        if (rval == null) {
+            // No previous instance of this class exists -- use the supplied
+            // instance, and place it in the table.
+            rval = service;
+            classToSingleton.put(service.getClass(), service);
+        }
+        return rval;
+    }
+}