Spring Batch: Writing data to multiple files with dynamic File Name

Question

I have a requirement to get the data from a database and write that data to files based on the filename given in the database.

This is how data is defined in the database:

Columns --> FILE_NAME, REC_ID, NAME
 Data --> file_1.csv, 1, ABC
 Data --> file_1.csv, 2, BCD
 Data --> file_1.csv, 3, DEF
 Data --> file_2.csv, 4, FGH
 Data --> file_2.csv, 5, DEF
 Data --> file_3.csv, 6, FGH
 Data --> file_3.csv, 7, DEF
 Data --> file_4.csv, 8, FGH

As you see, basically the file names along with the data is defined in the Database so what SpringBatch should do is get this data and write it to the corresponding file specified in the Database (i.e., file_1.csv should only contain 3 records (1,2,3), file_2.csv should only contain records 4 and 5, etc.)

Is it possible to use MultiResourceItemWriter for this requirement (please note that entire file name is dynamic and needs to be retrieved from Database).

Answer 1

I'm not sure but I don't think there is an easy way of obtaining this. You could try to build your own ItemWriter like this:

public class DynamicItemWriter  implements ItemStream, ItemWriter<YourEntry> {

    private Map<String, FlatFileItemWriter<YourEntry>> writers = new HashMap<>();

    private LineAggregator<YourEntry> lineAggregator;

    private ExecutionContext executionContext;

    @Override
    public void open(ExecutionContext executionContext) throws ItemStreamException {
        this.executionContext = executionContext;
    }

    @Override
    public void update(ExecutionContext executionContext) throws ItemStreamException {
    }

    @Override
    public void close() throws ItemStreamException {
        for(FlatFileItemWriter f:writers.values()){
            f.close();
        }
    }

    @Override
    public void write(List<? extends YourEntry> items) throws Exception {
        for (YourEntry item : items) {
            FlatFileItemWriter<YourEntry> ffiw = getFlatFileItemWriter(item);
            ffiw.write(Arrays.asList(item));
        }
    }

    public LineAggregator<YourEntry> getLineAggregator() {
        return lineAggregator;
    }

    public void setLineAggregator(LineAggregator<YourEntry> lineAggregator) {
        this.lineAggregator = lineAggregator;
    }


    public FlatFileItemWriter<YourEntry> getFlatFileItemWriter(YourEntry item) {
        String key = item.FileName();
        FlatFileItemWriter<YourEntry> rr = writers.get(key);
        if(rr == null){
            rr = new FlatFileItemWriter<>();
            rr.setLineAggregator(lineAggregator);
            try {
                UrlResource resource = new UrlResource("file:"+key);
                rr.setResource(resource);
                rr.open(executionContext);
            } catch (MalformedURLException e) {
                e.printStackTrace();
            }
            writers.put(key, rr);
            //rr.afterPropertiesSet();
        }
        return rr;
    }
}

and configure it as a writer:

<bean id="csvWriter" class="com....DynamicItemWriter">
        <property name="lineAggregator">
        <bean
         class="org.springframework.batch.item.file.transform.DelimitedLineAggregator">
            <property name="delimiter" value=","/>
            <property name="fieldExtractor" ref="csvFieldExtractor"/>
        </bean>
    </property>