private List<Float> getFileDataAsList(File targetFile, int interval) {
		if (!targetFile.exists()) {
			return Collections.emptyList();
		}

		List<Float> metrics = new ArrayList<>();
		try (BufferedReader br = new BufferedReader(new FileReader(targetFile))) {
			String data = br.readLine();
			int current = 0;
			while (StringUtils.isNotBlank(data)) {
				if (0 == current) {
					if (data.equals(NULL_STRING)) {
						metrics.add(null);
					} else {
						metrics.add(Float.parseFloat(data));
					}
				}
				if (++current >= interval) {
					current = 0;
				}
				data = br.readLine();
			}
		} catch (IOException e) {
			LOGGER.error("Report data retrieval is failed: {}", e.getMessage());
			LOGGER.debug("Trace is : ", e);
		}
		return metrics;
	}
Get files respectively if there are multiple tests.

@param testId test id
@param key    report key
@return return file list
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java