Tasklets are meant to perform a single task within a step. Our job will consist of several steps that execute one after the other. Each step should perform only one defined task.

Our job will consist of three steps:

Read lines from the input CSV file.

Calculate age for every person in the input CSV file.

Write name and age of each person to a new output CSV file.

Chunk approach performs actions over chunks of data. That is, instead of reading, processing and writing all the lines at once, it'll read, process and write a fixed amount of records (chunk) at a time

https://www.baeldung.com/spring-batch-tasklet-chunk