java - Spring Batch: org.springframework.batch.item.ReaderNotOpenException: Reader must be open before it can be read

Question

I read SO related questions but the solutions don't work for me.

I get the org.springframework.batch.item.ReaderNotOpenException: Reader must be open before it can be read exception.

Below is my configuration:

@Bean
@StepScope
public ItemReader<Player> reader(@Value("#{jobParameters[inputZipfile]}") String inputZipfile) {
                final String [] header = { .. this part omitted for brevity ... };
                FlatFileItemReader<Player> reader = new FlatFileItemReader<Player>();


                System.out.println(""+inputZipfile);

                reader.setResource(new ClassPathResource(inputZipfile));
                reader.setLineMapper(new DefaultLineMapper<Player>() {{
                    setLineTokenizer(new DelimitedLineTokenizer() {{
                        setNames( header );
                    }});
                    setFieldSetMapper(new BeanWrapperFieldSetMapper<Player>() {{
                        setTargetType(Player.class);
                    }});
                }});
                reader.setComments( header );
                return reader;
}

@Bean
@StepScope
public ItemProcessor<Player, PlayersStats> processor(@Value("#{jobParameters[statType]}") String statType,
                                                                 @Value("#{jobParameters[season]}") String season){
                PlayersStatsProcessor psp = new PlayersStatsProcessor();
                psp.setStatisticType( StatisticType.valueOf(statType) );
                psp.setSeason( season );
                return psp;
}


@Bean
@StepScope
public ItemWriter<PlayersStats> writer(){
            return new CustomWriter();
}


@Bean
public Job generateStatisticsJob() {

        return this.jobs.get("generateStatisticsJob")
                .incrementer(new RunIdIncrementer())
                .start(processPlayerStats())
                //.end()
                .build();
}

@Bean
public Step processPlayerStats() {
           return this.steps.get("processPlayerStats")        
                        .<Player, PlayersStats> chunk(10)
                        .reader(reader(null))
                        .processor(processor(null,null))
                        .writer(writer())
                        .build();
}

The inputZipFile variable is set properly and the file exists on the drive. I checked in the FlatFileItemReader code and the ReaderNotOpenException occurs when the reader member of the reader class is not set. The reader member is set in doOpen method. It looks that doOpen is not called. The question is why ?

Answer 1

The issue disappeared when I change the return type of my reader bean from Item to FlatFileItemReader. It is still not clear to me why this is a problem since chunk().reader() accepts ItemReader as an input. I assume that there is some AOP magic under the hood which does FlatFileReader init and matches by the return type.