ตัวอ่าน ตัวประมวลผล และตัวเขียน

The read-process-write triad

ItemReader interface

public interface ItemReader<T> {
    T read() throws Exception;
}

FlatFileItemReader

@Bean
public FlatFileItemReader<Person> reader() {
    return new FlatFileItemReaderBuilder<Person>()
            .name("personReader")
            .resource(new ClassPathResource("people.csv"))
            .delimited()
            .names("firstName", "lastName")
            .targetType(Person.class)
            .build();
}

JdbcCursorItemReader

@Bean
public JdbcCursorItemReader<Person> dbReader(DataSource ds) {
    return new JdbcCursorItemReaderBuilder<Person>()
            .name("dbReader")
            .dataSource(ds)
            .sql("SELECT first_name, last_name FROM people")
            .rowMapper(new PersonRowMapper())
            .build();
}

ItemProcessor interface

public interface ItemProcessor<I, O> {
    O process(I item) throws Exception;
}

Writing a processor

public class UpperCaseProcessor implements ItemProcessor<Person, Person> {
    @Override
    public Person process(Person p) {
        return new Person(p.getFirstName().toUpperCase(),
                          p.getLastName().toUpperCase());
    }
}

Filtering with the processor

public Person process(Person p) {
    if (p.getLastName().isBlank()) {
        return null; // drop this record
    }
    return p;
}

ItemWriter interface

public interface ItemWriter<T> {
    void write(Chunk<? extends T> chunk) throws Exception;
}

JdbcBatchItemWriter

@Bean
public JdbcBatchItemWriter<Person> writer(DataSource ds) {
    return new JdbcBatchItemWriterBuilder<Person>()
            .dataSource(ds)
            .sql("INSERT INTO people (first_name, last_name) VALUES (:firstName, :lastName)")
            .beanMapped()
            .build();
}

Wiring them into a step

return new StepBuilder("step1", repo)
        .<Person, Person>chunk(50, tx)
        .reader(reader())
        .processor(new UpperCaseProcessor())
        .writer(writer(ds))
        .build();

Custom readers and writers

Quick Check

Recap