kafka: set message key dynamically

[aarashtaheri]

Regarding the kafka sample code, currently you can only have one message key, which you set it in application.properties. After running the application there is no way to change it.

Is there a way to set the message key dynamically, before sending the message?

[garyrussell]

There are several options.

1 Delete this line:

handler.setMessageKeyExpression(new LiteralExpression(this.messageKey));

And change the send to ...

toKafka.send(new GenericMessage<>("foo" + i));

to

toKafka.send(MessageBuilder.withPayload("foo" + i)
    .setHeader(KafkaHeades.MESSAGE_KEY)
    .build());

If there is no key expression, we look for that header (same thing for the topic, partition).

2 Change this

handler.setMessageKeyExpression(new LiteralExpression(this.messageKey));

to

handler.setMessageKeyExpression(new SpelExpressionParser.parseExpression("<some expression>"));

Where <some expression> calculates the key - such as payload.key or headers['myHeader'].

[garyrussell]

See the README.