title: How to parse kafka message in KafkaSpout and set in tuple value
body: <p>I am trying to read kafka messages from KafkaSpout and set tuple values from json that are parsed from that message. Actually, I am creating an additional Bolt that parses a tuple field called &quot;value&quot; with json string from KafkaSpout. Is it possible to set these values in Spout?</p>
  <pre><code>class ScanConfigKafkaSpout(kafkaUrl: String, kafkaGroup: String, kafkaTopic: String) : KafkaSpout&lt;String, String&gt;(
      KafkaSpoutConfig
          .builder(kafkaUrl, kafkaTopic)
          .setProp(KEY_KAFKA_GROUP, &quot;grp1&quot;)
          .setProcessingGuarantee(KafkaSpoutConfig.ProcessingGuarantee.AT_MOST_ONCE)
          .build()
  ), ComponentId {
      override fun open(conf: MutableMap&lt;String, Any&gt;?, context: TopologyContext?, collector: SpoutOutputCollector?) {
          try {
              logger.debug(&quot;&lt;${id()}&gt; Opening ScanConfigKafkaSpout  with ${conf.toString()}&quot;)
              super.open(conf, context, collector)
              logger.debug(&quot;&lt;${id()}&gt; ScanConfigKafkaSpout opened&quot;)
          } catch (t: Throwable) {
              logger.error(&quot;&lt;${id()}&gt; Error during opening CrawlScanConfigKafkaSpout&quot;, t)
          }
      }
  
      override fun id(): String = SCAN_CONFIG_KAFKA_SPOUT
  
      companion object {
          private val logger = LoggerFactory.getLogger(ScanConfigKafkaSpout::class.java)
      }
  
  }
  </code></pre>