How to start a Spring Batch step inside a ItemProcessor - spring-boot

Question

Here is my scenario:
a1. read records from table A
a2. process these records one by one and generate a new temp table B for each record
b1. read records from table B, process these records data and save it in a file
a3. tag the record from table A as finished status
A pseudo code to describe this scenario:
foreach item in items:
1. select large amount data where id=item.id then save the result to temp table_id
2. process all records in table_id then write then to a file
3. update item status
4. send message to client
This is my design:
create a Spring Batch job, set a date as its parameter
create a step1 to read records from table A
create a step2 to read records from temporary table B and start it in the processor of step1
I check the Spring Batch docs, I didn't find any related introduction about how to nest a step into a step's processor. seems the Step is the minimum unit in Spring Batch and it cannot be split.
Update
Here is the pseudo code about what I did now to solve the problem:
(I'm using spring boot 2.7.8)
def Job:
PagingItemReader(id) :
select date from temp_id
FlatFileItemWriter:
application implement commandlinerunner:
items = TableAReposiroy.SelectAllBetweenDate
for item : items:
Service.createTempTableBWithId(item.id)
Service.loadDataToTempTable(item.id)
job = createJob(item.id)
luancher.run(job)
update item status

Answer 1

A step is part of a job. It is not possible to start a step from within an item processor.
You need to break your requirement into different steps, without trying to "nest" steps into each others. In your case, you can do something like:
create a Spring Batch job, set a date as its parameter
create a step1 to read records from table A and generate a new temp table B
create a step2 to read records from temporary table B, process these records data and save it in a file and tag the record from table A as finished status
The writer of step2 would be a composite writer: it writes data to the file AND updates the status of processed records in table A. This way, if there is an issue writing the file, the status of records in table A would be rolled back (in fact, they are not processed correctly as the write operation failed, in which case they need to be reprocessed).

Answer 2

You should have single job with two steps, stepA and stepB, spring batch does provide provision for controlled flow of execution of steps, you can sequentially execute two steps. For each item Once stepA reaches its writer and writes data, stepB will start. You can configure stepB to read data written by stepA.
You can also pass data between steps using Job Execution context, Once stepA ends put data in Job Execution context, it can be accessed in stepB once it starts. This can help in your case because you can pass item identifier which stepA picked for processing and pass it to stepB so that stepB can have this identifier in its writer to update its final status.