diff options
Diffstat (limited to 'policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java')
| -rw-r--r-- | policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java | 190 |
1 files changed, 91 insertions, 99 deletions
diff --git a/policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java b/policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java index d0b451f1..fa0a045c 100644 --- a/policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java +++ b/policy-utils/src/main/java/org/onap/policy/drools/utils/OrderedServiceImpl.java @@ -33,111 +33,103 @@ 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; +public class OrderedServiceImpl<T extends OrderedService> { + // logger + private static Logger logger = LoggerFactory.getLogger(OrderedServiceImpl.class); - // 'ServiceLoader' that is used to discover and create the services - private ServiceLoader<T> serviceLoader = null; + // sorted list of instances implementing the service + private List<T> implementers = 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<>(); + // 'ServiceLoader' that is used to discover and create the services + private ServiceLoader<T> serviceLoader = null; - /** - * 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); - } + // use this to ensure that we only use one unique instance of each class + @SuppressWarnings("rawtypes") + private static HashMap<Class,OrderedService> classToSingleton = new HashMap<>(); - /** - * @return the sorted list of services implementing interface 'T' discovered - * by 'ServiceLoader'. - */ - public synchronized List<T> getList() - { - if (implementers == null) - { - rebuildList(); - } - return implementers; - } + /** + * 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); + } - /** - * 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)); - } + /** + * 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; + } - // 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()); - } - }); + /** + * 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)); + } - // create an unmodifiable version of this list - implementers = Collections.unmodifiableList(tmp); - logger.info("***** OrderedServiceImpl implementers:\n {}", implementers); - return implementers; - } + // 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()); + } + }); - /** - * 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; - } + // 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; + } } |