Adding client class for sending message to topic

1) Adding TopicSinkClient class for sending messages to topic. The same
class will be used for PAP->PDP & PDP->PAP communication.

2) Once this review is through, will raise another one to remove
PdpClient from policy/pap.

Change-Id: I7253683d9e88885cfbe2ac9041d01da239b9321b
Issue-ID: POLICY-1443
Signed-off-by: ramverma <ram.krishna.verma@est.tech>

2 files changed, 155 insertions, 0 deletions

diff --git a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClient.java b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClient.java
new file mode 100644
index 00000000..3188b8d4
--- /dev/null
+++ b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClient.java
@@ -0,0 +1,104 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * ONAP PAP
+ * ================================================================================
+ * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
+ * Modifications Copyright (C) 2019 Nordix Foundation.
+ * ================================================================================
+ * 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.endpoints.event.comm.client;
+
+
+import java.util.List;
+
+import lombok.Getter;
+
+import org.onap.policy.common.endpoints.event.comm.TopicEndpoint;
+import org.onap.policy.common.endpoints.event.comm.TopicSink;
+import org.onap.policy.common.utils.coder.Coder;
+import org.onap.policy.common.utils.coder.CoderException;
+import org.onap.policy.common.utils.coder.StandardCoder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Client for sending messages to a Topic using TopicSink.
+ */
+public class TopicSinkClient {
+    private static final Logger logger = LoggerFactory.getLogger(TopicSinkClient.class);
+
+    /**
+     * Coder used to encode messages being sent to the topic.
+     */
+    private static final Coder CODER = new StandardCoder();
+
+    /**
+     * Topic to which messages are published.
+     */
+    @Getter
+    private final String topic;
+
+    /**
+     * Where messages are published.
+     */
+    private final TopicSink sink;
+
+    /**
+     * Constructs the object.
+     *
+     * @param topic topic to which messages should be published
+     * @throws TopicSinkClientException if the topic does not exist
+     */
+    public TopicSinkClient(final String topic) throws TopicSinkClientException {
+        this.topic = topic;
+
+        final List<TopicSink> lst = getTopicSinks(topic);
+        if (lst.isEmpty()) {
+            throw new TopicSinkClientException("no sinks for topic: " + topic);
+        }
+
+        this.sink = lst.get(0);
+    }
+
+    /**
+     * Sends a message to the topic, after encoding the message as json.
+     *
+     * @param message message to be encoded and sent
+     * @return {@code true} if the message was successfully sent/enqueued, {@code false} otherwise
+     */
+    public boolean send(final Object message) {
+        try {
+            final String json = CODER.encode(message);
+            return sink.send(json);
+
+        } catch (RuntimeException | CoderException e) {
+            logger.warn("send to {} failed because of {}", topic, e.getMessage(), e);
+            return false;
+        }
+    }
+
+    // the remaining methods are wrappers that can be overridden by junit tests
+
+    /**
+     * Gets the sinks for a given topic.
+     *
+     * @param topic the topic of interest
+     * @return the sinks for the topic
+     */
+    protected List<TopicSink> getTopicSinks(final String topic) {
+        return TopicEndpoint.manager.getTopicSinks(topic);
+    }
+}
diff --git a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClientException.java b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClientException.java
new file mode 100644
index 00000000..608393b3
--- /dev/null
+++ b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/TopicSinkClientException.java
@@ -0,0 +1,51 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * ONAP PAP
+ * ================================================================================
+ * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
+ * Modifications Copyright (C) 2019 Nordix Foundation.
+ * ================================================================================
+ * 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.endpoints.event.comm.client;
+
+/**
+ * Exception thrown by TopicSink client classes.
+ */
+public class TopicSinkClientException extends Exception {
+    private static final long serialVersionUID = 1L;
+
+    public TopicSinkClientException() {
+        super();
+    }
+
+    public TopicSinkClientException(final String message) {
+        super(message);
+    }
+
+    public TopicSinkClientException(final Throwable cause) {
+        super(cause);
+    }
+
+    public TopicSinkClientException(final String message, final Throwable cause) {
+        super(message, cause);
+    }
+
+    public TopicSinkClientException(final String message, final Throwable cause, final boolean enableSuppression,
+            final boolean writableStackTrace) {
+        super(message, cause, enableSuppression, writableStackTrace);
+    }
+
+}