[ONOS-4350] Inter Jar dependency implementation and code restructuring.

Change-Id: Iacac75e4187aed93ce1754c170a9c19707e5b8c3
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java
new file mode 100644
index 0000000..e7acccf
--- /dev/null
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java
@@ -0,0 +1,87 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * 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.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * units-stmt          = units-keyword sep string optsep stmtend
+ *
+ * ANTLR grammar rule
+ * unitsStatement : UNITS_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "units"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class UnitsListener {
+
+    /**
+     * Creates a new units listener.
+     */
+    private UnitsListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (units), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processUnitsEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.UnitsStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, UNITS_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_DATA:
+                YangLeaf leaf = (YangLeaf) tmpData;
+                leaf.setUnits(ctx.string().getText());
+                break;
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setUnits(ctx.string().getText());
+                break;
+            case TYPEDEF_DATA:
+                // TODO
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, UNITS_DATA,
+                                ctx.string().getText(), ENTRY));
+        }
+    }
+}
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