Add synchronized decorators for non-stream item readers/writers

[fmbenhassine]

Currently, Spring Batch provides two decorators (SynchronizedItemStreamReader and SynchronizedItemStreamWriter) to synchronize thread access to ItemStreamReader#read and ItemStreamWriter#write.

While those decorators work with ItemStreams, they are not usable with non item streams as they respectively accept ItemStreamReader and ItemStreamWriter as delegates. For example, those decorators cannot be used to synchronize access to ListItemReader#read (#3741) orKafkaItemWriter#write (#3970).

The goal of this issue is to add two decorators that accept ItemReader and ItemWriter as delegates and synchronize access to the read and write operations.

[hpoettker]

Are there already plans for the API to instantiate SynchronizedItemReader or SynchronizedItemWriter?

It should be consistent with the corresponding decorators for ItemStream, which can be instantiated with a no-args-constructor and a setter for the delegate, or a builder with a more fluent API. But in my opinion, both options feel a bit clunky today. Are there plans to allow more concise instanstiations like SynchronizedItemReader.of(delegate) or new SynchronizedItemReader(delegate)?

[fmbenhassine]

@hpoettker

Are there plans to allow more concise instanstiations like SynchronizedItemReader.of(delegate) or new SynchronizedItemReader(delegate)?

Yes, there will be a constructor that accepts the delegate.