PubSubItemWriter and PubSubItemReader for Spring Batch

[nklausen]

Is your feature request related to a problem? Please describe.
As a Spring batch developer, I want to be able to read and write to and from a Google PubSub, using the patterns in Spring Batch
https://docs.spring.io/spring-batch/docs/4.2.x/reference/html/readersAndWriters.html#itemReader
https://docs.spring.io/spring-batch/docs/4.2.x/reference/html/readersAndWriters.html#itemWriter

Describe the solution you'd like

Implementing a Google PubSubItemReader and PubSubItemWriter with builders similar to the once for Kafka

• KafkaItemReader
  • https://docs.spring.io/spring-batch/docs/4.2.x/reference/html/readersAndWriters.html#kafkaItemReader
    • https://github.com/spring-projects/spring-batch/blob/master/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/KafkaItemReader.java
    • https://github.com/spring-projects/spring-batch/blob/master/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/builder/KafkaItemReaderBuilder.java
• KafkaItemWriter
  • https://docs.spring.io/spring-batch/docs/4.2.x/reference/html/readersAndWriters.html#kafkaItemWriter
    • https://github.com/spring-projects/spring-batch/blob/master/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/KafkaItemWriter.java
    • https://github.com/spring-projects/spring-batch/blob/master/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/builder/KafkaItemWriterBuilder.java

Describe alternatives you've considered
N/A

Additional context
Like with #2509, it will help adoption of PubSub, if it was possible to use it in Spring Batch, with the same interface as the rest of the readers and writers.

[meltsufin]

I think this makes sense. We haven't yet provided any support for Spring Batch, but it's a pretty popular project in the Spring ecosystem. As always, contributions are welcome.

[nklausen]

Where do you see this belongs? is it a new project spring-cloud-gcp-batch under the spring-cloud-gcp umbrella?

[meltsufin]

I think I would just put it under /spring-cloud-gcp-pubsub in the org.springframework.cloud.gcp.pubsub.batch package.