Spring Batch：如何在侦听器方法中从 ItemReader 手动读取项目？

Question

I'm looking for a way to use an ItemReader in an @AfterStep listener method to check the database for a specific status for items being processed in the batch job. (The items are child objects of a row in another table, and those parent objects are not handled in the batch job step.) I'm currently using a JdbcCursorItemReader to perform SQL against an H2 database.

However, I'm not sure how to just read a line from the resultset, or if I need to programmatically open/close the JdbcCursorItemReader , as I'm simply using the ItemReader<T> interface to represent it. The only method I have access to that way is read() . Should I cast as JdbcCursorItemReader<T> instead, and open/read each item/close? Is it possible to get the chunk size from the step execution object in order to process these in chunks?

I realize this isn't an ideal way to do this, but I need to be able to do this after every step, and it would, IMO, unnecessarily complicate the Java config to add a separate RPW step after each existing step to do this.

In short, what I would like to do in the @AfterStep listener is:

1. Update failed items from the step. (This is already working by keeping a list in the listener of failed items on skip, and using a separate ItemWriter to write the errored items.)
2. (Assuming the ItemWriter commits after write(), or that the db is able to be read "dirty") - Use an ItemReader to read in all parent objects where all the child objects have a FAILED status.
3. Change the parent status to FAILED and write using an existing ItemWriter for the parent.

However, I don't know how to read items from the ItemReader (and properly maintaining the cursor), whether individually or in a collection. The StepBuilderFactory.reader() method builds the reader in the step config and Spring Batch magic does the rest. Using an ItemWriter in a listener method seems pretty straight-forward, and write(Collection<T> items) just seems to work. I was just hoping someone here might know how to correctly read items from the ItemReader in this way.

Thanks in advance!

Answer 1

Yes, casting is an option. Something like this should work:

if (reader instanceof ItemStreamReader) {
    (ItemStreamReader) reader.open(new ExecutionContext());
}
while((in = reader.read()) != null) {
    <do what you need here>
}
if (reader instanceof ItemStreamReader) {
    (ItemStreamReader) reader.close();
}