No Issue : Internal Refactoring to improve code readability.

[chickenchickenlove]

Motivation:

• There are some codes using *.size() > 0 or *.size() == 0 in spring-kafka.
• There is code where the constructor could be reused, but it was not.
• There is code where a null value can occur, but it does not indicate that null is possible.

Modifications:

• Replace a.size() > 0 with !a.isEmpty().
• Replace a.size() == 0 with a.isEmpty().
• Reuse constructor already existed to remove duplicate constructor logic.
• Add @nullable annotations to field, and method. Also, add warning log.

Result:

• There is only one side effect which developer can observe.
  • when BatchMessagingMessageListenerAdapter#setBatchMessageConverter() is executed, new warning log can be occur.

[chickenchickenlove]

FYI

RecordMessageConverter can be null. Please refer to codes below.

// BatchMessagingMessageConverter.java
	public BatchMessagingMessageConverter() {
		this(null);
	}

	public BatchMessagingMessageConverter(RecordMessageConverter recordConverter) {
		this.recordConverter = recordConverter;
		if (JacksonPresent.isJackson2Present()) {
			this.headerMapper = new DefaultKafkaHeaderMapper();
		}
	}

Then, getRecordMessageConverter() can return null.
BatchMessagingMessageListenerAdapter#setBatchMessageConverter() call getRecordMessageConverter() internally to set messageConverter.

If user created BatchMessagingMessageConverter by using default constructor, there is no message converter even if BatchMessagingMessageListenerAdapter#setBatchMessageConverter() is completed without any warning logs.