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Diffstat (limited to 'policy-utils/src/main/java/org/onap/policy/drools/utils/PropertyUtil.java')
-rw-r--r-- | policy-utils/src/main/java/org/onap/policy/drools/utils/PropertyUtil.java | 385 |
1 files changed, 385 insertions, 0 deletions
diff --git a/policy-utils/src/main/java/org/onap/policy/drools/utils/PropertyUtil.java b/policy-utils/src/main/java/org/onap/policy/drools/utils/PropertyUtil.java new file mode 100644 index 00000000..9cfe2ed1 --- /dev/null +++ b/policy-utils/src/main/java/org/onap/policy/drools/utils/PropertyUtil.java @@ -0,0 +1,385 @@ +/*- + * ============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.onap.policy.drools.utils; + +import java.io.File; +import java.io.FileInputStream; +import java.io.IOException; +import java.util.HashMap; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.Properties; +import java.util.Set; +import java.util.Timer; +import java.util.TimerTask; + +/** + * This class provides utilities to read properties from a properties + * file, and optionally get notifications of future changes + */ +public class PropertyUtil +{ + /** + * Read in a properties file + * @param file the properties file + * @return a Properties object, containing the associated properties + * @throws IOException - subclass 'FileNotFoundException' if the file + * does not exist or can't be opened, and 'IOException' if there is + * a problem loading the properties file. + */ + static public Properties getProperties(File file) throws IOException + { + // create an InputStream (may throw a FileNotFoundException) + FileInputStream fis = new FileInputStream(file); + try + { + // create the properties instance + Properties rval = new Properties(); + + // load properties (may throw an IOException) + rval.load(fis); + return(rval); + } + finally + { + // close input stream + fis.close(); + } + } + + /** + * Read in a properties file + * @param fileName the properties file + * @return a Properties object, containing the associated properties + * @throws IOException - subclass 'FileNotFoundException' if the file + * does not exist or can't be opened, and 'IOException' if there is + * a problem loading the properties file. + */ + static public Properties getProperties(String fileName) throws IOException + { + return(getProperties(new File(fileName))); + } + + /* ============================================================ */ + + // timer thread used for polling for property file changes + private static Timer timer = null; + + /** + * This is the callback interface, used for sending notifications of + * changes in the properties file. + */ + public interface Listener + { + /** + * Notification of a properties file change + * @param properties the new properties + * @param the set of property names that have changed, including + * additions and removals + */ + void propertiesChanged(Properties properties, Set<String> changedKeys); + } + + // this table maps canonical file into a 'ListenerRegistration' instance + static private HashMap<File, ListenerRegistration> registrations = + new HashMap<File, ListenerRegistration>(); + + /** + * This is an internal class - one instance of this exists for each + * property file that is being monitored. Note that multiple listeners + * can be registered for the same file. + */ + private static class ListenerRegistration + { + // the canonical path of the file being monitored + File file; + + // the most recent value of 'file.lastModified()' + long lastModified; + + // the most recent set of properties + Properties properties; + + // the set of listeners monitoring this file + LinkedList<Listener> listeners; + + // the 'TimerTask' instance, used for periodic polling + TimerTask timerTask; + + /** + * Constructor - create a 'ListenerRegistration' instance for this + * file, but with no listeners + */ + ListenerRegistration(File file) throws IOException + { + this.file = file; + + // The initial value of 'lastModified' is set to 0 to ensure that we + // correctly handle the case where the file is modified within the + // same second that polling begins. + lastModified = 0; + + // fetch current properties + properties = getProperties(file); + + // no listeners yet + listeners = new LinkedList<Listener>(); + + // add to static table, so this instance can be shared + registrations.put(file, this); + + if (timer == null) + { + // still need to create a timer thread + synchronized(PropertyUtil.class) + { + // an additional check is added inside the 'synchronized' block, + // just in case someone beat us to it + if (timer == null) + { + timer = new Timer("PropertyUtil-Timer", true); + } + } + } + + // create and schedule the timer task, so this is periodically polled + timerTask = new TimerTask() + { + public void run() + { + try + { + poll(); + } + catch (Exception e) + { + System.err.println(e); + } + } + }; + timer.schedule(timerTask, 10000L, 10000L); + } + + /** + * Add a listener to the notification list + * @param listener this is the listener to add to the list + * @return the properties at the moment the listener was added to the list + */ + synchronized Properties addListener(Listener listener) + { + listeners.add(listener); + return((Properties)properties.clone()); + } + + /** + * Remove a listener from the notification list + * @param listener this is the listener to remove + */ + synchronized void removeListener(Listener listener) + { + listeners.remove(listener); + + // See if we need to remove this 'ListenerRegistration' instance + // from the table. The 'synchronized' block is needed in case + // another listener is being added at about the same time that this + // one is being removed. + synchronized(registrations) + { + if (listeners.size() == 0) + { + timerTask.cancel(); + registrations.remove(file); + } + } + } + + /** + * This method is periodically called to check for property list updates + * @throws IOException if there is an error in reading the properties file + */ + synchronized void poll() throws IOException + { + long timestamp = file.lastModified(); + if (timestamp != lastModified) + { + // update the record, and send out the notifications + lastModified = timestamp; + + // Save old set, and initial set of changed properties. + Properties oldProperties = properties; + HashSet<String> changedProperties = + new HashSet<String>(oldProperties.stringPropertyNames()); + + // Fetch the list of listeners that we will potentially notify, + // and the new properties. Note that this is in a 'synchronized' + // block to ensure that all listeners receiving notifications + // actually have a newer list of properties than the one + // returned on the initial 'getProperties' call. + properties = getProperties(file); + + Set<String> newPropertyNames = properties.stringPropertyNames(); + changedProperties.addAll(newPropertyNames); + + // At this point, 'changedProperties' is the union of all properties + // in both the old and new properties files. Iterate through all + // of the entries in the new properties file - if the entry + // matches the one in the old file, remove it from + // 'changedProperties'. + for (String name : newPropertyNames) + { + if (properties.getProperty(name).equals + (oldProperties.getProperty(name))) + { + // Apparently, any property that exists must be of type + // 'String', and can't be null. For this reason, we don't + // need to worry about the case where + // 'properties.getProperty(name)' returns 'null'. Note that + // 'oldProperties.getProperty(name)' may be 'null' if the + // old property does not exist. + changedProperties.remove(name); + } + } + + // 'changedProperties' should be correct at this point + if (changedProperties.size() != 0) + { + // there were changes - notify everyone in 'listeners' + for (final Listener notify : listeners) + { + // Copy 'properties' and 'changedProperties', so it doesn't + // cause problems if the recipient makes changes. + final Properties tmpProperties = + (Properties)(properties.clone()); + final HashSet<String> tmpChangedProperties = + new HashSet<String>(changedProperties); + + // Do the notification in a separate thread, so blocking + // won't cause any problems. + new Thread() + { + public void run() + { + notify.propertiesChanged + (tmpProperties, tmpChangedProperties); + } + }.start(); + } + } + } + } + } + + /** + * Read in a properties file, and register for update notifications. + * NOTE: it is possible that the first callback will occur while this + * method is still in progress. To avoid this problem, use 'synchronized' + * blocks around this invocation and in the callback -- that will ensure + * that the processing of the initial properties complete before any + * updates are processed. + * + * @param file the properties file + * @param notify if not null, this is a callback interface that is used for + * notifications of changes + * @return a Properties object, containing the associated properties + * @throws IOException - subclass 'FileNotFoundException' if the file + * does not exist or can't be opened, and 'IOException' if there is + * a problem loading the properties file. + */ + static public Properties getProperties(File file, Listener listener) + throws IOException + { + if (listener == null) + { + // no listener specified -- just fetch the properties + return(getProperties(file)); + } + + // Convert the file to a canonical form in order to avoid the situation + // where different names refer to the same file. + file = file.getCanonicalFile(); + + // See if there is an existing registration. The 'synchronized' block + // is needed to handle the case where a new listener is added at about + // the same time that another one is being removed. + synchronized(registrations) + { + ListenerRegistration reg = registrations.get(file); + if (reg == null) + { + // a new registration is needed + reg = new ListenerRegistration(file); + } + return(reg.addListener(listener)); + } + } + + /** + * Read in a properties file, and register for update notifications. + * NOTE: it is possible that the first callback will occur while this + * method is still in progress. To avoid this problem, use 'synchronized' + * blocks around this invocation and in the callback -- that will ensure + * that the processing of the initial properties complete before any + * updates are processed. + * + * @param fileName the properties file + * @param notify if not null, this is a callback interface that is used for + * notifications of changes + * @return a Properties object, containing the associated properties + * @throws IOException - subclass 'FileNotFoundException' if the file + * does not exist or can't be opened, and 'IOException' if there is + * a problem loading the properties file. + */ + static public Properties getProperties(String fileName, Listener listener) + throws IOException + { + return(getProperties(new File(fileName), listener)); + } + + /** + * Stop listenening for updates + * @param file the properties file + * @param notify if not null, this is a callback interface that was used for + * notifications of changes + */ + static public void stopListening(File file, Listener listener) + { + if (listener != null) + { + ListenerRegistration reg = registrations.get(file); + if (reg != null) + { + reg.removeListener(listener); + } + } + } + + /** + * Stop listenening for updates + * @param fileName the properties file + * @param notify if not null, this is a callback interface that was used for + * notifications of changes + */ + static public void stopListening(String fileName, Listener listener) + { + stopListening(new File(fileName), listener); + } + +} |