Spring batch - processing a subset of multiple items at once

Question

I have a list of numerous items that I split into chunks of 10 each.
But the itemProcessor only processes 1 by 1 item in a chunk.

How can I aggregate all items in each chunk into a list and then make a call (contains that list) to the external API because I don't want 1 API request per 1 item?

@Bean
public Job job(JobBuilderFactory jobs, StepBuilderFactory steps) {
    return jobs.get("job")
            .start(steps.get("step")
                    .<Item, Item>chunk(10)
                    .reader(itemReader())
                    .processor(itemProcessor())
                    .writer(itemWriter())
                    .build())
            .build();
}

Answer 1

Solved it.
I reconfigure the ItemReader to return the "chunk" that needs to be processed

Job.java

@Bean
public Job job(JobBuilderFactory jobs, StepBuilderFactory steps) {
    return jobs.get("job")
            .start(steps.get("step")
                    .<List<Item>, List<Item>chunk(1) // Use chunk size of 1, as the reader now returns a chunk
                    .reader(itemReader())
                    .processor(itemProcessor())
                    .writer(itemWriter())
                    .build())
            .build();
}

@Bean
@StepScope
public ItemReader<List<Item>> itemReader() {
        // Prepare the items from your data source ...

        int chunkSize = 10; // Set your desired chunk size here
        return new ChunkItemReader<>(items, chunkSize);
    }

ChunkItemReader.java

import org.springframework.batch.item.ItemReader;

import java.util.List;

public class ChunkItemReader<T> implements ItemReader<List<T>> {

    private final List<T> items;
    private final int chunkSize;
    private int currentIndex;

    public ChunkItemReader(List<T> items, int chunkSize) {
        this.items = items;
        this.chunkSize = chunkSize;
        this.currentIndex = 0;
    }

    @Override
    public List<T> read() {
        int endIndex = Math.min(currentIndex + chunkSize, items.size());
        if (currentIndex < endIndex) {
            List<T> chunk = items.subList(currentIndex, endIndex);
            currentIndex = endIndex;
            return chunk;
        }
        return null; // End of data
    }
}