3

我有一个由我正在编写的程序以外的程序创建的 CSV 文件，因此我无法更改标题。该文件的标题是ControllerID,Event,Number,ReaderID,Timestamp,TransactionID,. CSVPrinter我已经为我用来将一行插入到同一个 CSV文件中指定了相同的标题。但是，当打印机添加记录时，它会在新记录之前添加一个标题行，如下所示：

0,1,2688229830,3,2018-09-03 13:54,63
ControllerID,Event,Number,ReaderID,Timestamp,TransactionID
0,1,4900920,2,2018-09-03,15:15,176492

有问题的代码如下所示：

/* Add an entry to the TransactionLog CSV */
private static boolean logTransaction (
  int cid, int rid, boolean freeExit, long tsMS, long accNum, String reason
) {
  boolean added = false;
  int evt = freeExit ? 8 : 1;
  File transactLog = new File(Locations.getDatabaseDir(), "TransactLog.csv"),

  CSVFormat shortFormat = CSVFormat.DEFAULT.withQuote(null)
    .withAllowMissingColumnNames(true)/*.withTrailingDelimiter(true)*/
    .withHeader(Transaction.getHeader(false));
  // Attempt to read the last transaction ID and add 1 to it, to be used as ID of new transaction
  try (
    CSVParser shortParser = new CSVParser(new FileReader(transactLog), shortFormat);
    CSVPrinter shortWriter = new CSVPrinter(new FileWriter(transactLog, true), shortFormat);
  ) {
    // read in all the current records, getting the transactionID of the last record
    List<CSVRecord> shortRecords = shortParser.getRecords();
    int newTransId = 1;
    if (!shortRecords.isEmpty()) {
      CSVRecord last = shortRecords.get(shortRecords.size() - 1);
      String lastTransactionId = last.get("TransactionID");
      // add one to last transaction ID
      try {
        newTransId = Integer.parseInt(lastTransactionId) + 1;
      } catch (IllegalArgumentException IAEx) {
        newTransId = shortRecords.size() + 1;
        LOGGER.warn("Failed to determine last transaction ID from CSV ("
          + lastTransactionId + "); setting to recordCount (" + newTransId + ") ..."
        );
      }
    }
    // write the new transaction record
    Transaction t = new Transaction(cid, evt, accNum, rid, tsMS, newTransId, reason);
    List<String> tValues = t.asList(false), fValues = t.asList(true);
    shortWriter.printRecord(tValues);
    shortWriter.flush();
    added = true;
  } catch (IOException IOEx) {
    added = false;
    LOGGER.error(Util.getErrorTrace(
      "Failed to write transaction to \"" + transactLog.getAbsolutePath() + "\" CSV", IOEx
    ));
  }

  return added;
}

事务 POJO 的代码被省略，因为它与问题无关。

如何防止在CSVPrinter输出行之前输出标题行？（CSV 文件已包含标题行。）

4

1 回答 1

6

为了不输出标题行，您需要添加.withSkipHeaderRecord(true)到与CSVFormat一起使用的实例中CSVPrinter，如下所示：

CSVFormat skipFormat = CSVFormat.DEFAULT.withQuote(null)
  .withAllowMissingColumnNames(true).withTrailingDelimiter(true)
  .withHeader(Transaction.getHeader(false))
  .withSkipHeaderRecord(true).withIgnoreEmptyLines(true);

调用.withIgnoreEmptyLines(true)是可选的。包含它是为了不保留空行/空白行。

注意：如果要将标题行作为文件的第一行输出，则在创建文件时，可以更改.withSkipHeaderRecord(true)为.withSkipHeaderRecord(csvFile.exists()). 这是因为文件在创建之前不存在，但在下一次写入记录时确实存在。

于 2018-09-03T13:52:47.430 回答