Reading from streams instead of files in spring batch itemReader - spring-batch

Question

I am getting a csv file as a webservice call which needs to be laoded. Right now I am saving it in temp directory to provide it as setResource to Reader.
Is there a way to provide stream(byte[]) as is instead of saving the file first?

Answer 1

The method setResource of the ItemReader takes a org.springframework.core.io.Resource as a parameter. This class has a few out-of-the-box implementations, among which you can find org.springframework.core.io.InputStreamResource. This class' constructor takes a java.io.InputStream which can be implemented by java.io.ByteArrayInputStream.
So technically, yes you can consume a byte[] parameter in an ItemReader.
Now, for how to actually do that, here are a few ideas :
1) Create your own FlatFileItemReader (since CSV is a flat file) and make it implement StepExecutionListener
public class CustomFlatFileItemReader<T> extends FlatFileItemReader<T> implements StepExecutionListener {
}
2) Override the beforeStep method, do your webservice call within and save the result in a variable
private byte[] stream;
#Override
public void beforeStep(StepExecution stepExecution) {
// your webservice logic
stream = yourWebservice.results();
}
3) Override the setResource method to pass this stream as the actual resource.
#Override
public void setResource(Resource resource) {
// Convert byte array to input stream
InputStream is = new ByteArrayInputStream(stream);
// Create springbatch input stream resource
InputStreamResource res = new InputStreamResource(is);
// Set resource
super.setResource(res);
}
Also, if you don't want to call your webservice within the ItemReader, you can simply store the byte array in the JobExecutionContext and get it in the beforeStep method with stepExecution.getJobExecution().getExecutionContext().get("key");

Answer 2

I am doing right now with FlaFileItemReader, reading a file from Google Storage. No needed to extends:
#Bean
#StepScope
public FlatFileItemReader<MyDTO> itemReader(#Value("#{jobParameters['filename']}") String filename) {
InputStream stream = googleStorageService.getInputStream(GoogleStorage.UPLOADS, filename);
return new FlatFileItemReaderBuilder<MyDTO>()
.name("myItemReader")
.resource(new InputStreamResource(stream)) //InputStream here
.delimited()
.names(FIELDS)
.lineMapper(lineMapper()) // Here is mapped like a normal File
.fieldSetMapper(new BeanWrapperFieldSetMapper<MyDTO>() {{
setTargetType(MyDTO.class);
}})
.build();
}