[JAVA] I want to perform aggregation processing with spring-batch


In a WEB application made with Spring-Boot I want to implement such batch processing that aggregates the contents of the prepared API execution log file and stores the result in the DB. However, there is no site that can be used as a reference for implementing that requirement, and it is ridiculously clogged, so I will leave it as a memorandum. (I don't know if this is the best)

Main requirements

Prerequisite data (example)

Before: Log format to be aggregated

ʻURL / HTTP method / HTTP status code / execution time / execution date and timeat the time of access are listed in TSV format. Example: / api / ・ ・ ・ GET 200 48 2020/08/14 11:05:42 701 / api / ・ ・ ・ GET 200 27 2020/08/14 11:05:43 352 / api / ・ ・ ・ ・ / 41 DELETE 401 10 2020/08/14 11:05:46 780 / api / ・ ・ ・ / 42 PUT 200 108 2020/08/14 11:06:16 824 / api / ・ ・ ・ POST 500 806 2020/08/14 11:06:30 252 ・ ・ ・ `

After: Format when storing DB





Dto class

public class LogCollectedDto {
  //API name
  private String apiName;
  //HTTP method
  private String httpMethod;
  //HTTP status code
  private String httpCode;
  //Execution time(ms)
  private String executionTime;
  //Aggregation date and time
  private String collectedDate;


Defined in Bean

  public FlatFileItemReader<LogCollectedDto> reader() {

    final String READ_FILE_PATH = <Log file name to read>;

    FlatFileItemReader<LogCollectedDto> reader = new FlatFileItemReader<>();
    reader.setResource(new FileSystemResource(READ_FILE_PATH));
        new DefaultLineMapper() {
                new DelimitedLineTokenizer(DelimitedLineTokenizer.DELIMITER_TAB) {
                        new String[] {
                          "apiUrl", "httpMethod", "httpCode", "executionTime", "collectedDate"
                new BeanWrapperFieldSetMapper<LogCollectedDto>() {
    return reader;


Cut out to another class

public class CustomItemProcessor implements ItemProcessor<LogCollectedDto, LogCollectedDto> {

  public LogCollectedDto process(LogCollectedDto item) throws Exception {

    //Validation of the retrieved Item, skip that line if false
    if (!validateItem(item)) {
      return null;

    //Hold the acquired Item once in another variable for processing later
    //(If you modify the argument directly, the Item acquired when interrupting and restarting may become the processed data)
    LogCollectedDto afterItem = item;
    //Data content processing (separate method omitted)
    afterItem.setApiName(getApiName(・ ・ ・));

    return afterItem;




Cut out to another class

public class CustomItemWriter extends JpaItemWriter<LogCollectedDto> {

  private final JpaItemWriter<Log> jpaItemWriter;

  public void write(List<? extends LogCollectedDto> items) {

   //Aggregate the Items received from the Processor and pass it to another Writer instance
    Map<String, List<LogCollectedDto>> groupingMap = groupingItems(items);

   *Grouping Items received from Processor
   *API name and HTTP status as composite key
   * @param list
   * @return
  private Map<String, List<LogCollectedDto>> groupingItems(List<? extends LogCollectedDto> list) {
    //Create a composite key
    Function<LogCollectedDto, String> compositeKey =
        logDto -> {
          StringBuffer sb = new StringBuffer();
          return sb.toString();

    Map<String, List<LogCollectedDto>> grpByComplexKeys =

    return grpByComplexKeys;

   *Generate a list of Entity by aggregating grouped items
   * @param groupingMap
   * @return
  private List<Log> collectItems(Map<String, List<LogCollectedDto>> groupingMap) {

    List<Log> recordList = new ArrayList<>();

    for (List<LogCollectedDto> dtoList : groupingMap.values()) {
      //Instantiation of Entity class
      Log record = new Log();
      //Aggregation processing
                  Collectors.averagingDouble(dto -> Double.parseDouble(dto.getExecutionTime()))));

    return recordList;



There are concerns, but I personally think it's the cleanest way to write. We are always looking for opinions. Conclusion: Stream API is the strongest! !! !!

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