How do I create custom ItemReader for each step in my Spring Batch project - spring-batch

Question

I am trying to use a custom reader, processor and writer in each step:
public Step step1(StepBuilderFactory factory,
ItemReader reader,
ExpireAssessmentWriter writer,
AssessmentItemProcessor processor,
PlatformTransactionManager platformTransactionManager){
return stepBuilderFactory.get("step1")
.transactionManager(platformTransactionManager)
.<Assessment,Assessment>chunk(10)
.reader(reader)
.processor(processor)
.writer(writer)
.build();
}
//update aggregate balance table
#Bean
public Step step2(StepBuilderFactory factory,
ItemReader reader,
BalanceItemWriter writer,
BalanceProcessor processor,
PlatformTransactionManager platformTransactionManager){
return stepBuilderFactory.get("step2")
.transactionManager(platformTransactionManager)
.<Assessment,Assessment>chunk(10)
.reader(reader)
.processor(processor)
.writer(writer)
.build();
}
#Bean
public Step step3(StepBuilderFactory factory,
ItemReader<Assessment> reader,
CustomWriter3 writer,
CustomItemProcessor3 processor,
PlatformTransactionManager platformTransactionManager){
return stepBuilderFactory.get("step3")
.transactionManager(platformTransactionManager)
.<Assessment,Assessment>chunk(10)
.reader(reader)
.processor(processor)
.writer(writer)
.build();
}
The first steps works fine but thats only when I leave this reader in the same class:
private static final String READER_QUERY = "SELECT * FROM TABLE1 WHERE COLUMN='TEST'";
#Bean
public JdbcCursorItemReader<Assessment> reader(DataSource dataSource) {
return new JdbcCursorItemReaderBuilder<Assessment>()
.dataSource(dataSource)
.name("AssessmentUtilityReader")
.sql(READER_QUERY)
.rowMapper(new AssessmentMapper())
.build();
}
How can I create a custom reader for each of these steps that will read it's own query?
Can I create a custom reader that extends JdbcCursorItemReader
and returns this same snippet of code? :
#Bean
public JdbcCursorItemReader<Assessment> reader(DataSource dataSource) {
return new JdbcCursorItemReaderBuilder<Assessment>()
.dataSource(dataSource)
.name("AssessmentUtilityReader")
.sql(READER_QUERY)
.rowMapper(new AssessmentMapper())
.build();
}
```

Answer 1

Since the item type is the same for all steps, you can create a method that accepts a query and returns an item reader:
public JdbcCursorItemReader<Assessment> getReader(DataSource dataSource, String query) {
return new JdbcCursorItemReaderBuilder<Assessment>()
.dataSource(dataSource)
.name("AssessmentUtilityReader") // can be passed as a parameter as well
.sql(query)
.rowMapper(new AssessmentMapper())
.build();
}
Then call this method in each step definition and pass the required query for each step.

Answer 2

To Turn your reader in a custom component, which can be autowired, add the following class:
#Component
public class AssessmentUtilityReader extends JdbcCursorItemReader<Assessment> {
public AssessmentUtilityReader(final DataSource dataSource) {
setName(getClass().getSimpleName());
setDataSource(dataSource);
setRowMapper(new AssessmentMapper());
// language=SQL
setSql(
"""
SELECT *
FROM TABLE1
WHERE COLUMN = 'TEST'
""");
}
}
Hint: The Comment (// language=SQL) is an hint for IntelliJ to use SQL highlighting in the following lines. It's optional.
Simply autowire in steps definition:
#Bean
public Step step3(StepBuilderFactory factory,
AssessmentUtilityReader<Assessment> assessmentUtilityReader,
CustomWriter3 writer,
CustomItemProcessor3 processor,
PlatformTransactionManager platformTransactionManager){
return stepBuilderFactory.get("step3")
.transactionManager(platformTransactionManager)
.<Assessment,Assessment>chunk(10)
.reader(assessmentUtilityReader)
.processor(processor)
.writer(writer)
.build();
}