如何在Logstash中将JSON对象转换为字符串？

我从Logstash 6.5中得到了以下输出：

{ "field1": 1, "field2": "test" }

我想把以前的JSON对象转换成字符串，那么我该怎么做呢

编辑1：这是我的完整管道，我想向RabbitMQ发送一个字符串，但我的输出发送一个JSON对象

input {
    jdbc {
        jdbc_driver_library => "${CDC_JDBC_DRIVER_FILE}"
        jdbc_driver_class => "${CDC_JDBC_DRIVER_CLASS_MIDAS}"
        jdbc_connection_string => "jdbc:informix-sqli://${CDC_BD_HOST_MIDAS}:${CDC_BD_PORT_MIDAS}/${CDC_BD_NAME_INICIAL_MIDAS}:${CDC_SERVER_MIDAS}=${CDC_BD_ALLOCATE_MIDAS}"
        jdbc_user => "${CDC_BD_USER_MIDAS}"
        jdbc_password => "${CDC_BD_PWD_MIDAS}"
        statement_filepath => "${CDC_PATH_QUERY_MIDAS}"
        jdbc_default_timezone => "America/Mexico_City"
        ##schedule => "30 */2 * * *"
    }
}

filter {
    ruby {
        code => '
            event.set("ProductCustomFields",
                {
                    "CustomField" => [
                        {
                            "Name" => "precio_venta_act",
                            "Value" => event.get("precio_venta_actual")
                        }
                    ]
                }
            )
        '
    }
    mutate {
        remove_field => [
            "precio_venta_actual",
            "precio_venta_inicial",
            etc
        ]
    }
}

output {
    rabbitmq {
        automatic_recovery => true
        connection_timeout => 60000 
        exchange => "${CDC_RABBITMQ_EXCHANGE}"
        exchange_type => "${CDC_RABBITMQ_EXCHANGE_TYPE}"
        host => "${CDC_RABBITMQ_HOST}"
        key => "${CDC_RABBITMQ_ROUTING_KEY}"
        password => "${CDC_RABBITMQ_PASSWORD}"
        port => "${CDC_RABBITMQ_PORT}"
        ssl => true
        ssl_certificate_password => "${CDC_RABBITMQ_CERT_PASS}"
        ssl_certificate_path => "${CDC_RABBITMQ_CERT_PATH}"
        user => "${CDC_RABBITMQ_USER}"
        vhost => "${DCD_RABBITMQ_VHOST}"
    }
}

---

如果您使用“output{stdout{codec=>rubydebug}}”，那么这些字段是什么样子的？您可以添加完整的管道吗？您的数据源是什么？感谢您的回答，我已经添加了完整的管道，输入是JDBC，输出是RabbitMQ