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authorJim Hahn <jrh3@att.com>2019-03-20 17:58:49 -0400
committerJim Hahn <jrh3@att.com>2019-03-21 10:12:53 -0400
commit4ac697769f46e3f6d52a086bcc8e15d89755dd0d (patch)
treea6a7028dd9d288730610afd1d556a646eff8afb4 /utils/src/main/java
parent6fb97d3373232c16823f374d637533d36ac1049c (diff)
Add simple Registry class to manage singletons
Typically, singleton classes have lots of static methods, or use a getInstance() method to get the singleton. This provides an alternative mechanism, similar to the JDNI and the common-paramater property registry, where singletons can be registered. Clean up registry after junit test. Modified a few comments. (I prefer 90 characters for comments.) Added a method to register or replace an existing key without throwing an exception. Change-Id: I3b62719013d3b5f71adb5e9299d3c1257fb55c80 Issue-ID: POLICY-1542 Signed-off-by: Jim Hahn <jrh3@att.com>
Diffstat (limited to 'utils/src/main/java')
-rw-r--r--utils/src/main/java/org/onap/policy/common/utils/services/Registry.java151
1 files changed, 151 insertions, 0 deletions
diff --git a/utils/src/main/java/org/onap/policy/common/utils/services/Registry.java b/utils/src/main/java/org/onap/policy/common/utils/services/Registry.java
new file mode 100644
index 00000000..c209379f
--- /dev/null
+++ b/utils/src/main/java/org/onap/policy/common/utils/services/Registry.java
@@ -0,0 +1,151 @@
+/*
+ * ============LICENSE_START=======================================================
+ * ONAP
+ * ================================================================================
+ * 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.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This is a simple object registry, similar in spirit to JNDI, but suitable for use in a
+ * stand-alone JVM.
+ */
+public class Registry {
+ private static final Logger logger = LoggerFactory.getLogger(Registry.class);
+
+ private static volatile Registry instance = new Registry();
+
+ /**
+ * Registry map.
+ */
+ private Map<String, Object> name2object = new ConcurrentHashMap<>();
+
+ /**
+ * Constructs the object.
+ */
+ private Registry() {
+ super();
+ }
+
+ /**
+ * Registers an object.
+ *
+ * @param name name by which the object is known
+ * @param object object to be registered
+ * @throws IllegalStateException if an object is already registered for that name
+ * @throws IllegalArgumentException if either argument is null
+ */
+ public static void register(String name, Object object) {
+ if (name == null) {
+ throw new IllegalArgumentException("attempt to register: " + name);
+ }
+
+ if (object == null) {
+ throw new IllegalArgumentException("attempt to register null object for " + name);
+ }
+
+ instance.name2object.compute(name, (key, oldval) -> {
+
+ if (oldval != null) {
+ throw new IllegalStateException("already registered: " + name);
+ }
+
+ return object;
+ });
+ }
+
+ /**
+ * Registers an object, replacing any previously existing binding.
+ *
+ * @param name name by which the object is known
+ * @param object object to be registered
+ * @throws IllegalArgumentException if either argument is null
+ */
+ public static void registerOrReplace(String name, Object object) {
+ if (name == null) {
+ throw new IllegalArgumentException("attempt to register: " + name);
+ }
+
+ if (object == null) {
+ throw new IllegalArgumentException("attempt to register null object for " + name);
+ }
+
+ instance.name2object.compute(name, (key, oldval) -> {
+
+ if (oldval != null) {
+ logger.warn("replacing previously registered: {}", name);
+ }
+
+ return object;
+ });
+ }
+
+ /**
+ * Unregisters an object.
+ *
+ * @param name name by which the object is known
+ * @return {@code true} if the object was unregistered, {@code false} if it did not
+ * exist
+ */
+ public static boolean unregister(String name) {
+ return (instance.name2object.remove(name) != null);
+ }
+
+ /**
+ * Gets the object by the given name.
+ *
+ * @param name name of the object to get
+ * @param clazz object's class
+ * @return the object
+ * @throws IllegalArgumentException if no object is registered by the given name
+ */
+ public static <T> T get(String name, Class<T> clazz) {
+ Object obj = instance.name2object.get(name);
+ if (obj == null) {
+ throw new IllegalArgumentException("not registered: " + name);
+ }
+
+ return clazz.cast(obj);
+ }
+
+ /**
+ * Gets the object by the given name, providing a default value if the name is not
+ * registered.
+ *
+ * @param name name of the object to get
+ * @param clazz object's class
+ * @param defaultVal the default value to return, if the object does not exist
+ * @return the object, if it exists, the default value, otherwise
+ */
+ public static <T> T getOrDefault(String name, Class<T> clazz, T defaultVal) {
+ Object obj = instance.name2object.get(name);
+ return (obj != null ? clazz.cast(obj) : defaultVal);
+ }
+
+ /**
+ * Creates a new registry instance. This is typically only used by junit tests, as it
+ * discards any previous registry entries.
+ */
+ public static void newRegistry() {
+ instance = new Registry();
+ }
+}