[SPARK-48148][CORE] JSON objects should not be modified when read as STRING

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/json/JacksonParser.scala

@@ -280,13 +280,32 @@ class JacksonParser(
         case VALUE_STRING =>
           UTF8String.fromString(parser.getText)
 
-        case _ =>
+        case other =>
           // Note that it always tries to convert the data as string without the case of failure.
-          val writer = new ByteArrayOutputStream()
-          Utils.tryWithResource(factory.createGenerator(writer, JsonEncoding.UTF8)) {
-            generator => generator.copyCurrentStructure(parser)
+          val startLocation = parser.getTokenLocation
+          startLocation.contentReference().getRawContent match {
+            case byteArray: Array[Byte] =>
+               other match {
+                case START_OBJECT =>
+                  parser.skipChildren()
+                case START_ARRAY =>
+                  parser.skipChildren()
+                case _ =>
+                   // Do nothing in this case; we've already read the token
+              }
+              val endLocation = parser.currentLocation.getByteOffset
+
+              UTF8String.fromBytes(
+                byteArray,
+                startLocation.getByteOffset.toInt,
+                endLocation.toInt - (startLocation.getByteOffset.toInt))
+            case _ =>
+              val writer = new ByteArrayOutputStream()
+              Utils.tryWithResource(factory.createGenerator(writer, JsonEncoding.UTF8)) {
+                generator => generator.copyCurrentStructure(parser)
+              }
+              UTF8String.fromBytes(writer.toByteArray)
           }
-          UTF8String.fromBytes(writer.toByteArray)
       }
 
     case TimestampType =>

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala

@@ -3865,6 +3865,24 @@ abstract class JsonSuite
       }
     }
   }
+
+  test("SPARK-48148: decimal precision is preserved when object is read as string") {
+    withTempPath { path =>
+
+      val granularFloat = "-999.99999999999999999999999999999999995"
+      val jsonString = s"""{"data": {"v": ${granularFloat}}}, {"data": {"v": ${granularFloat}}}]"""
+
+      Seq(jsonString).toDF()
+        .repartition(1)
+        .write
+        .text(path.getAbsolutePath)
+
+      val df = spark.read.schema("data STRING").json(path.getAbsolutePath)
+
+      val expected = s"""{"v": ${granularFloat}}"""
+      checkAnswer(df, Seq(Row(expected)))
+    }
+  }
 }
 
 class JsonV1Suite extends JsonSuite {