Sending json events to kafka in non-stringified format

问题

I have created a dataframe like below, where I have used to_json() method to create JSON array value.

+---------------------------------------------------------------------------------------------------- 

|json_data                                                                                                  |
+-----------------------------------------------------------------------------------------------------------+
|{"name":"sensor1","value-array":[{"time":"2020-11-27T01:01:00.000Z","sensorvalue":11.0,"tag1":"tagvalue"}]}|
+-----------------------------------------------------------------------------------------------------------+

I am using the below method to send the dataframe to a kafka topic. But when I consume the data which has been sent to the kafka topic, I could see the json data got stringified.

Code to push the data to kafka:

outgoingDF.selectExpr("CAST(Key as STRING) as key", "to_json(struct(*)) AS value")
        .write
        .format("kafka")
        .option("topic", "topic_test")
        .option("kafka.bootstrap.servers", "localhost:9093")
        .option("checkpointLocation", checkpointPath)
        .option("kafka.sasl.mechanism", "PLAIN")
        .option("kafka.security.protocol", "SASL_SSL")
        .option("truncate", false)
        .save()

Stringified data being received in kafka:

{
    "name": "sensor1",
    "value-array": "[{\"time\":\"2020-11-27T01:01:00.000Z\",\"sensorvalue\":11.0,\"tag1\":\"tagvalue\"}]"
}

How can we send the data to kafka topic, so that we dont see stringified jsons as output ?

回答1:

json_data is of type string & again you are passing json_data to to_json(struct("*")) function.

Check value column which is going to kafka.

df.withColumn("value",to_json(struct($"*"))).show(false)
+-----------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
|json_data                                                                                                  |value                                                                                                                                      |
+-----------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
|{"name":"sensor1","value-array":[{"time":"2020-11-27T01:01:00.000Z","sensorvalue":11.0,"tag1":"tagvalue"}]}|{"json_data":"{\"name\":\"sensor1\",\"value-array\":[{\"time\":\"2020-11-27T01:01:00.000Z\",\"sensorvalue\":11.0,\"tag1\":\"tagvalue\"}]}"}|
+-----------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+

Try below code.

 df
 .withColumn("value-array",array(struct($"time",$"sensorvalue",$"tag1")))
 .selectExpr("CAST(Key as STRING) as key",to_json(struct($"name",$"value-array")).as("value"))
 .write
 .format("kafka")
 .option("topic", "topic_test")
 .option("kafka.bootstrap.servers", "localhost:9093")
 .option("checkpointLocation", checkpointPath)
 .option("kafka.sasl.mechanism", "PLAIN")
 .option("kafka.security.protocol", "SASL_SSL")
 .option("truncate", false)
 .save()

来源：https://stackoverflow.com/questions/65101659/sending-json-events-to-kafka-in-non-stringified-format

标签

apache-spark

spark-structured-streaming