[SPARK-10196] [SQL] Correctly saving decimals in internal rows to JSON.

https://issues.apache.org/jira/browse/SPARK-10196

Author: Yin Huai <yhuai@databricks.com>

Closes #8408 from yhuai/DecimalJsonSPARK-10196.

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/json/JacksonGenerator.scala

@@ -95,7 +95,7 @@ private[sql] object JacksonGenerator {
       case (FloatType, v: Float) => gen.writeNumber(v)
       case (DoubleType, v: Double) => gen.writeNumber(v)
       case (LongType, v: Long) => gen.writeNumber(v)
-      case (DecimalType(), v: java.math.BigDecimal) => gen.writeNumber(v)
+      case (DecimalType(), v: Decimal) => gen.writeNumber(v.toJavaBigDecimal)
       case (ByteType, v: Byte) => gen.writeNumber(v.toInt)
       case (BinaryType, v: Array[Byte]) => gen.writeBinary(v)
       case (BooleanType, v: Boolean) => gen.writeBoolean(v)

sql/hive/src/test/scala/org/apache/spark/sql/sources/JsonHadoopFsRelationSuite.scala

@@ -17,6 +17,8 @@
 
 package org.apache.spark.sql.sources
 
+import java.math.BigDecimal
+
 import org.apache.hadoop.fs.Path
 
 import org.apache.spark.deploy.SparkHadoopUtil
@@ -75,4 +77,29 @@ class JsonHadoopFsRelationSuite extends HadoopFsRelationTest {
       )
     }
   }
+
+  test("SPARK-10196: save decimal type to JSON") {
+    withTempDir { file =>
+      file.delete()
+
+      val schema =
+        new StructType()
+          .add("decimal", DecimalType(7, 2))
+
+      val data =
+        Row(new BigDecimal("10.02")) ::
+          Row(new BigDecimal("20000.99")) ::
+          Row(new BigDecimal("10000")) :: Nil
+      val df = createDataFrame(sparkContext.parallelize(data), schema)
+
+      // Write the data out.
+      df.write.format(dataSourceName).save(file.getCanonicalPath)
+
+      // Read it back and check the result.
+      checkAnswer(
+        read.format(dataSourceName).schema(schema).load(file.getCanonicalPath),
+        df
+      )
+    }
+  }
 }