Spring Batch 3 Custom Writer with a List

Question

Imagine a Menu.java pojo with 3 fields: id, name and telephone.

I'm using Spring Batch 3. My processor returns me a List. And I want to write on a file these values of each object of the list.

If Menu wasn't a list, this would be my writer class:

@Bean(name="MyWriter")
@SphynxBatchStepScope
public FlatFileItemWriter<Menu> myWriter() String fileOutputName) {

    FlatFileItemWriter<Menu> writer = new FlatFileItemWriter<Menu>();   
    writer.setResource(new FileSystemResource("test.txt")));
    DelimitedLineAggregator<Menu> delLineAgg = new DelimitedLineAggregator<Menu>();
    delLineAgg.setDelimiter("          ");
    BeanWrapperFieldExtractor<Menu> fieldExtractor = new BeanWrapperFieldExtractor<Menu>();
    fieldExtractor.setNames(new String[] {"id", "name", "telephone"});
    delLineAgg.setFieldExtractor(fieldExtractor);
    writer.setLineAggregator(delLineAgg);
    writer.setHeaderCallback(header());
    writer.setFooterCallback(footer());
    writer.setEncoding("UTF-8");

    return writer;
}

But if I want to covert this class to works with a List how can I do it?

I can't find any solution. Only this:

Using an ItemWriter with List of Lists

But I don't see how implement this. For example, where and how call to setDelegate method. Or when I need to put my "id", "name", "telephone" sequence.

Please, does anybody knows a code example with a custom Writer with List?

Thanks in advance

Note that I use Spring Batch 3 with annotations, without xml config file — user3525459, May 10 '17 at 14:09

Dean Clark · Accepted Answer · 2017-05-10T15:32:39.743

Your writer would stay as is but be wrapped by the ListUnpackingItemWriter.

// NOTE: this will now be the delegate used by the delegating writer.
// It will be injected to the delegating writer.
@Bean(name="MyDelegateWriter")
@SphynxBatchStepScope
public FlatFileItemWriter<Menu> myWriter(String fileOutputName) {

    FlatFileItemWriter<Menu> writer = new FlatFileItemWriter<Menu>();   
    writer.setResource(new FileSystemResource("test.txt")));
    DelimitedLineAggregator<Menu> delLineAgg = new DelimitedLineAggregator<Menu>();
    delLineAgg.setDelimiter("          ");
    BeanWrapperFieldExtractor<Menu> fieldExtractor = new BeanWrapperFieldExtractor<Menu>();
    fieldExtractor.setNames(new String[] {"id", "name", "telephone"});
    delLineAgg.setFieldExtractor(fieldExtractor);
    writer.setLineAggregator(delLineAgg);
    writer.setHeaderCallback(header());
    writer.setFooterCallback(footer());
    writer.setEncoding("UTF-8");

    return writer;
}

// NOTE: now this "MyWriter" will be used by your job
@Bean(name="MyWriter")
@SphynxBatchStepScope
public ListUnpackingItemWriter(@Qualifier("MyDelegateWriter") FlatFileItemWriter<Menu> delegate) {
    ListUnpackingItemWriter<List<Menu>> writer = new ListUnpackingItemWriter<>();
    writer.setDelegate(delegate);
    return writer;
}

Hi dean.. can you please provide me xml configuration of the same ? — Shekhar Jadhav, Jul 25 '18 at 05:49

Spring Batch 3 Custom Writer with a List

1 Answers1