[SPARK-12195][SQL] Adding BigDecimal, Date and Timestamp into Encoder

This PR is to add three more data types into Encoder, including `BigDecimal`, `Date` and `Timestamp`.

marmbrus cloud-fan rxin Could you take a quick look at these three types? Not sure if it can be merged to 1.6. Thank you very much!

Author: gatorsmile <gatorsmile@gmail.com>

Closes #10188 from gatorsmile/dataTypesinEncoder.

sql/catalyst/src/main/scala/org/apache/spark/sql/Encoder.scala

@@ -97,6 +97,24 @@ object Encoders {
    */
   def STRING: Encoder[java.lang.String] = ExpressionEncoder()
 
+  /**
+    * An encoder for nullable decimal type.
+    * @since 1.6.0
+    */
+  def DECIMAL: Encoder[java.math.BigDecimal] = ExpressionEncoder()
+
+  /**
+    * An encoder for nullable date type.
+    * @since 1.6.0
+    */
+  def DATE: Encoder[java.sql.Date] = ExpressionEncoder()
+
+  /**
+    * An encoder for nullable timestamp type.
+    * @since 1.6.0
+    */
+  def TIMESTAMP: Encoder[java.sql.Timestamp] = ExpressionEncoder()
+
   /**
    * Creates an encoder for Java Bean of type T.
    *

sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java

@@ -18,6 +18,9 @@
 package test.org.apache.spark.sql;
 
 import java.io.Serializable;
+import java.math.BigDecimal;
+import java.sql.Date;
+import java.sql.Timestamp;
 import java.util.*;
 
 import scala.Tuple2;
@@ -385,6 +388,20 @@ public class JavaDatasetSuite implements Serializable {
     Assert.assertEquals(data3, ds3.collectAsList());
   }
 
+  @Test
+  public void testPrimitiveEncoder() {
+    Encoder<Tuple5<Double, BigDecimal, Date, Timestamp, Float>> encoder =
+      Encoders.tuple(Encoders.DOUBLE(), Encoders.DECIMAL(), Encoders.DATE(), Encoders.TIMESTAMP(),
+        Encoders.FLOAT());
+    List<Tuple5<Double, BigDecimal, Date, Timestamp, Float>> data =
+      Arrays.asList(new Tuple5<Double, BigDecimal, Date, Timestamp, Float>(
+        1.7976931348623157E308, new BigDecimal("0.922337203685477589"),
+          Date.valueOf("1970-01-01"), new Timestamp(System.currentTimeMillis()), Float.MAX_VALUE));
+    Dataset<Tuple5<Double, BigDecimal, Date, Timestamp, Float>> ds =
+      context.createDataset(data, encoder);
+    Assert.assertEquals(data, ds.collectAsList());
+  }
+
   @Test
   public void testTypedAggregation() {
     Encoder<Tuple2<String, Integer>> encoder = Encoders.tuple(Encoders.STRING(), Encoders.INT());