Implement REST API of policy

Change-Id: I46f5a3cd6d66cf7a3a90a5d153b3878fdf5cbd31
diff --git a/impl/src/main/java/org/onosproject/segmentrouting/policy/api/DropPolicyCodec.java b/impl/src/main/java/org/onosproject/segmentrouting/policy/api/DropPolicyCodec.java
new file mode 100644
index 0000000..407bd08
--- /dev/null
+++ b/impl/src/main/java/org/onosproject/segmentrouting/policy/api/DropPolicyCodec.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2021-present Open Networking 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.
+ */
+package org.onosproject.segmentrouting.policy.api;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+
+import org.onosproject.codec.CodecContext;
+import org.onosproject.codec.JsonCodec;
+
+/**
+ * Codec of DropPolicy class.
+ */
+public final class DropPolicyCodec extends JsonCodec<DropPolicy> {
+
+    // JSON field names
+    public static final String POLICY_ID = "policy_id";
+    public static final String POLICY_TYPE = "policy_type";
+
+    @Override
+    public ObjectNode encode(DropPolicy policy, CodecContext context) {
+        final ObjectNode result = context.mapper().createObjectNode()
+                .put(POLICY_ID, policy.policyId().toString())
+                .put(POLICY_TYPE, policy.policyType().toString());
+
+        return result;
+    }
+
+    @Override
+    public DropPolicy decode(ObjectNode json, CodecContext context) {
+        return new DropPolicy();
+    }
+}