Safe Template Group Object

    The Group object is added which will be
    used by Training and Prediction templates

Change-Id: Idd3e2cce80b5698ce6071c74f0895c0021b0daf3
diff --git a/apps/aiplugin/api/src/main/java/org/onosproject/aiplugin/Group.java b/apps/aiplugin/api/src/main/java/org/onosproject/aiplugin/Group.java
new file mode 100644
index 0000000..fd11a1f
--- /dev/null
+++ b/apps/aiplugin/api/src/main/java/org/onosproject/aiplugin/Group.java
@@ -0,0 +1,143 @@
+/*
+ * Copyright 2024-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 aiplugin.api;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.annotation.JsonPOJOBuilder;
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Immutable class representing a Group with fields and an action.
+ */
+@JsonIgnoreProperties(ignoreUnknown = true)
+@JsonDeserialize(builder = Group.Builder.class)
+public final class Group {
+    private List<String> fields;
+    private String action;
+
+    /**
+     * Private constructor for the Group class.
+     *
+     * @param builder The Builder object providing field values.
+     */
+    private Group(Builder builder) {
+        this.fields = builder.fields;
+        this.action = builder.action;
+    }
+
+    /**
+     * Returns the fields of the group.
+     *
+     * @return A list of fields.
+     */
+    public List<String> getFields() {
+        return fields;
+    }
+
+    /**
+     * Returns the action associated with the group.
+     *
+     * @return The action as a string.
+     */
+    public String getAction() {
+        return action;
+    }
+
+    /**
+     * Static method to create a new Builder instance.
+     *
+     * @return A new Builder for creating a Group instance.
+     */
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Builder class for Group.
+     */
+    @JsonPOJOBuilder(withPrefix = "", buildMethodName = "build")
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    public static class Builder {
+        private List<String> fields = new ArrayList<>();
+        private String action;
+
+        /**
+         * Adds or appends a list of fields to the Group.
+         * If fields already exist, this method appends the new list to them.
+         *
+         * @param fields A list of field names.
+         * @return The Builder instance.
+         */
+        public Builder fields(List<String> fields) {
+            this.fields.addAll(fields);
+            return this;
+        }
+
+        /**
+         * Adds a single field to the Group.
+         * This method allows adding fields one by one.
+         *
+         * @param field A single field name.
+         * @return The Builder instance.
+         */
+        public Builder fields(String field) {
+            this.fields.add(field);
+            return this;
+        }
+
+        /**
+         * Sets the action of the Group.
+         *
+         * @param action The action as a string.
+         * @return The Builder instance.
+         */
+        public Builder action(String action) {
+            this.action = action;
+            return this;
+        }
+
+        /**
+         * Builds the Group instance.
+         * Before creating the Group, it checks that fields and action are not null.
+         *
+         * @return A new Group instance.
+         */
+        public Group build() {
+            Preconditions.checkNotNull(action, "Action cannot be null");
+            Preconditions.checkNotNull(fields, "Fields cannot be null");
+            Preconditions.checkArgument(!fields.isEmpty(), "Fields cannot be empty");
+            return new Group(this);
+        }
+    }
+
+    /**
+     * Generates a string representation of the Group.
+     *
+     * @return A string representation of the Group.
+     */
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+                .add("fields", fields)
+                .add("action", action)
+                .toString();
+    }
+}