DriverManager.getConnection(
           "jdbc:mysql://" + host + "/" + dbName
           + "?useUnicode=true&characterEncoding=utf8_spanish_ci",
    user, pass);

strSQL = "select convert(cast(a.json_data as char) using 'utf8') as json_data "
       + "from mi_tabla "
       + "where id = ?";
try(PreparedStatement ps = conn.prepareStatement(strSQL)) {
    /*
       Mi código para leer la tabla
     */
}