public static String getJSONString(Object o, ObjectInspector oi) {
    return getJSONString(o, oi, JSON_NULL);
  }
Convert a Object to a standard Java object in compliance with JDBC 3.0 (see JDBC 3.0
Specification, Table B-3: Mapping from JDBC Types to Java Object Types).

This method is kept consistent with HiveResultSetMetaData#hiveTypeToSqlType .
serde/src/java/org/apache/hadoop/hive/serde2/SerDeUtils.java