The settings of the properties field have the same problem, and SpEL expressions cannot solve it

[linchutao]

Affects Version(s): <Spring for Apache Kafka version>

[linchutao]

#361

[artembilan]

I'm sorry what is the problem? Can you be, please, more specific?
Otherwise this looks like Invalid and will be closed respectively.

Thank you for understanding!

[linchutao]

Sorry, let me show you a demo

@KafkaListener(groupId = "my-group", topics = "#{'${consumer-config.topics}'.split(',')}", properties = "#{'${consumer-config.properties}'.split(',')}")

with

application.yml

consumer-config:  
  topics: topic1,topic2  
  properties: max.poll.records:100,group.instance.id:instance1

properties cannot be processed normally like topics，I noticed that the processing of properties in the source code is not the same as topics

[garyrussell]

Unlike the other properties that support SpEL, there is no mention of SpEL in the javadocs for properties.

	/**
	 * Kafka consumer properties; they will supersede any properties with the same name
	 * defined in the consumer factory (if the consumer factory supports property overrides).
	 * <p>
	 * <b>Supported Syntax</b>
	 * <p>The supported syntax for key-value pairs is the same as the
	 * syntax defined for entries in a Java
	 * {@linkplain java.util.Properties#load(java.io.Reader) properties file}:
	 * <ul>
	 * <li>{@code key=value}</li>
	 * <li>{@code key:value}</li>
	 * <li>{@code key value}</li>
	 * </ul>
	 * {@code group.id} and {@code client.id} are ignored.
	 * @return the properties.
	 * @since 2.2.4
	 * @see org.apache.kafka.clients.consumer.ConsumerConfig
	 * @see #groupId()
	 * @see #clientIdPrefix()
	 */
	String[] properties() default {};

Vs

	/**
	 * The topics for this listener.
	 * The entries can be 'topic name', 'property-placeholder keys' or 'expressions'.
	 * An expression must be resolved to the topic name.
	 * This uses group management and Kafka will assign partitions to group members.
	 * <p>
	 * Mutually exclusive with {@link #topicPattern()} and {@link #topicPartitions()}.
	 * @return the topic names or expressions (SpEL) to listen to.
	 */
	String[] topics() default {};

This would be a new feature.

[linchutao]

Thanks @garyrussell , This is how I deal with it now

@KafkaListener(groupId = "my-group",
        topics = "#{'${consumer-config.topics}'.split(',')}",
        properties = {
        "max.poll.records:" + "${consumer-config.properties.max.poll.records}", 
            "group.instance.id:" + "${consumer-config.properties.group.instance.id}"
    })

with

consumer-config:
  topics: topic1,topic2
  properties:
    max.poll.records: 100
    group.instance.id: instance1

It works, but the configuration looks a little cumbersome

[garyrussell]

Understood; this is a reasonable new feature request.

[garyrussell]

@linchutao I have implemented the change, but FYI, this works with current versions:

application.properties:

some.prop=max.poll.records: 10\nfetch.min.bytes: 123456

or

some.prop=max.poll.records: 10\n \
 fetch.min.bytes: 123456

	@KafkaListener(id = "kgh1880", topics = "kgh1880", autoStartup = "false",
			properties = "${some.prop}")

i.e. insert a newline between properties

[garyrussell]

application.yml

some:
  prop: |
    max.poll.records: 10
    fetch.min.bytes: 123456