如何在Spring Batch中同时读取两个文件

@Configuration
@EnableBatchProcessing
public class BatchConfiguration {

    @Autowired
    private JobBuilderFactory jobBuilderFactory;

    @Autowired
    private StepBuilderFactory stepBuilderFactory;

    @Bean
    public ItemReader<String> file1Reader() {
        FlatFileItemReader<String> reader = new FlatFileItemReader<>();
        reader.setResource(new FileSystemResource("file1.txt"));
        reader.setLineMapper(new PassThroughLineMapper());
        return reader;
    }

    @Bean
    public ItemReader<String> file2Reader() {
        FlatFileItemReader<String> reader = new FlatFileItemReader<>();
        reader.setResource(new FileSystemResource("file2.txt"));
        reader.setLineMapper(new PassThroughLineMapper());
        return reader;
    }

    @Bean
    public ItemProcessor<String, String> processor() {
        return item -> item.toUpperCase();
    }

    @Bean
    public ItemWriter<String> writer() {
        FlatFileItemWriter<String> writer = new FlatFileItemWriter<>();
        writer.setResource(new FileSystemResource("output.txt"));
        writer.setLineAggregator(new PassThroughLineAggregator<>());
        return writer;
    }

    @Bean
    public Step step1(ItemReader<String> file1Reader, ItemProcessor<String, String> processor, ItemWriter<String> writer) {
        return stepBuilderFactory.get("step1")
                .<String, String>chunk(10)
                .reader(file1Reader)
                .processor(processor)
                .writer(writer)
                .build();
    }

    @Bean
    public Step step2(ItemReader<String> file2Reader, ItemProcessor<String, String> processor, ItemWriter<String> writer) {
        return stepBuilderFactory.get("step2")
                .<String, String>chunk(10)
                .reader(file2Reader)
                .processor(processor)
                .writer(writer)
                .build();
    }

    @Bean
    public Job job(Step step1, Step step2) {
        return jobBuilderFactory.get("job")
                .start(step1)
                .next(step2)
                .build();
    }
}