Spring: How to import data via CSV

In this article, I want to show you how you can import data via a CSV file in a cloud based application.

Spring controller

In order to upload the CSV file, we will use an HTTP POST request with mime type as multipart/form-data.

This request will be processed by my spring rest controller.

I will get the file via the request parameter with type : MultipartFile.

If the file content is not empty, I can extract the bytes and encode them as Base64 encoding using java 8 utility.

In order to do the work outside of a user-facing request, I use the Google Cloud Platform (GCP) task queues mechanism.

I can pass the encoded content as a task parameter. In parallel to the user facing request, a servlet will do the job with the specified parameter.

	@RestController
	@RequestMapping("/assessment-equipments")
	public class AssessmentEquipmentController {
	private final AssessmentEquipmentService assessmentEquipmentService;
	private final AssessmentMeasureService assessmentMeasureService;
	public AssessmentEquipmentController(AssessmentEquipmentService assessmentEquipmentService,
	AssessmentMeasureService assessmentMeasureService) {
	this.assessmentEquipmentService = assessmentEquipmentService;
	this.assessmentMeasureService = assessmentMeasureService;
	}
	@PostMapping("/{id}/uncertainties")
	public ResponseEntity<String> saveUncertainties(@NotNull @PathVariable Long id,
	@RequestParam("file") MultipartFile file) {
	if (file.isEmpty()) {
	return new ResponseEntity<>("Please select a file!", HttpStatus.OK);
	}
	try {
	byte[] content = file.getBytes();
	Queue queue = QueueFactory.getDefaultQueue();
	queue.add(TaskOptions.Builder.withUrl("/admin/assessment-measures")
	.param("id", String.valueOf(id))
	.param("csv", Base64.getEncoder().encodeToString(content)));
	return new ResponseEntity<>("The CSV file for the assessment equipment with ID [" + id + "] will be processed soon.", HttpStatus.OK);
	} catch (IOException e) {
	return new ResponseEntity<>("Oops something goes wrong!", HttpStatus.CONFLICT);
	}
	}
	}

view raw spring_csv_controller hosted with ❤ by GitHub

Servlet Consumer

The servlet is pretty straightforward :

1. It extracts the encoded content
2. It decode the encoded content
3. It loads object list from the CSV content (jackson csv)
4. It calls a service with the list of objects 

	@WebServlet(
	name = "AssessmentMeasureImporter",
	description = "Import CSV file for assessment measure",
	urlPatterns = "/admin/assessment-measures"
	)
	public class AssessmentMeasureImporter extends HttpServlet {
	@Autowired
	private AssessmentMeasureService assessmentMeasureService;
	public void init(ServletConfig config) throws ServletException {
	super.init(config);
	SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this,
	config.getServletContext());
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response) {
	Long id = ServletUtils.getLongParameter(request, "id");
	byte[] content = ServletUtils.getBytesParameter(request, "csv");
	List<AssessmentMeasureDto> assessmentMeasures = CsvUtils
	.loadObjectList(AssessmentMeasureDto.class, content);
	assessmentMeasureService.saveByAssessmentEquipment(id, assessmentMeasures);
	response.setStatus(200);
	}
	}

view raw spring_csv_servlet hosted with ❤ by GitHub

CSV Utility

In the servlet, I've called a utility method for reading the CSV content into an array of Objects.

I use for this purpose the Jackson library.

	<dependency>
	<groupId>com.fasterxml.jackson.dataformat</groupId>
	<artifactId>jackson-dataformat-csv</artifactId>
	<version>2.9.9</version>
	</dependency>

view raw jackson_csv_maven hosted with ❤ by GitHub

	public static <T> List<T> loadObjectList(Class<T> type, byte[] content) {
	Assert.notNull(type,"type must not be null");
	Assert.notNull(content,"content must not be null");
	try {
	CsvSchema schema = CsvSchema.emptySchema().withHeader();
	CsvMapper mapper = new CsvMapper();
	MappingIterator<T> readValues = mapper.readerFor(type)
	.with(schema).readValues(content);
	return readValues.readAll();
	} catch (Exception e) {
	return Collections.emptyList();
	}
	}

view raw load_csv_objects hosted with ❤ by GitHub

Happy learning...