add java api for date

Author: adrian-wang

sql/core/src/main/java/org/apache/spark/sql/api/java/DataType.java

@@ -44,6 +44,11 @@ public abstract class DataType {
    */
   public static final BooleanType BooleanType = new BooleanType();
 
+  /**
+   * Gets the DateType object.
+   */
+  public static final DateType DateType = new DateType();
+
   /**
    * Gets the TimestampType object.
    */

sql/core/src/main/java/org/apache/spark/sql/api/java/DateType.java

@@ -0,0 +1,27 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.spark.sql.api.java;
+
+/**
+ * The data type representing java.sql.Timestamp values.
+ *
+ * {@code TimestampType} is represented by the singleton object {@link DataType#TimestampType}.
+ */
+public class DateType extends DataType {
+    protected DateType() {}
+}

sql/core/src/main/scala/org/apache/spark/sql/types/util/DataTypeConversions.scala

@@ -41,6 +41,7 @@ protected[sql] object DataTypeConversions {
     case StringType => JDataType.StringType
     case BinaryType => JDataType.BinaryType
     case BooleanType => JDataType.BooleanType
+    case DateType => JDataType.DateType
     case TimestampType => JDataType.TimestampType
     case DecimalType => JDataType.DecimalType
     case DoubleType => JDataType.DoubleType
@@ -80,6 +81,8 @@ protected[sql] object DataTypeConversions {
       BinaryType
     case booleanType: org.apache.spark.sql.api.java.BooleanType =>
       BooleanType
+    case dateType: org.apache.spark.sql.api.java.DateType =>
+      DateType
     case timestampType: org.apache.spark.sql.api.java.TimestampType =>
       TimestampType
     case decimalType: org.apache.spark.sql.api.java.DecimalType =>