Question

如何向CSV文件添加新列，并在每列中添加计算数据？

示例

userid,expDate 1,012015 2,022016 3,032018

我会从每一行中获取expDate，计算它相对于当前月份和年份，以获得到期前的几个月，然后是圆形月份（所以月份下个月将是1，无论是第1天还是最后一天当月）

userid,expDate,monthsTill 1,022017,0 2,032017,1 3,042017,2 3,052017,3

你也会如何“跳过”各列中具有特定值的行？

Answer 1

基于你的伪代码，这里应该做什么诀窍

private void process(){
    BufferedReader bufferedReader = null;
    PrintWriter p = null;
    String sep = ",";
    String newCol = "monthsTill";
    String defaultTillExpMonth = ">3";
    Calendar cal = Calendar.getInstance();
    cal.setTime(new Date());
    int currMonth = cal.get(Calendar.MONTH) + 1;
    try {
    // read csv file
    List<String> input = new ArrayList<String>();
   File inputFile = new File("InputFile");
  bufferedReader = new BufferedReader(new FileReader(inputFile));
    String readLine = "";
    while ((readLine = bufferedReader.readLine()) != null) {
        input.add(readLine);
    }

 // for each row after first row
    // calculate timeTillExpired
        // if format MYYYY (ex 22017)
            // M and YYYY -> MM and YYYY

       // calculate relative to current date as months

    int numOfRecords = input.size();
    if(numOfRecords>1){
        List<String> output = new ArrayList<String>();
        String header = input.get(0) +sep +newCol;
        output.add(header);

        // for each row after first row
        // calculate timeTillExpired
        // if format MYYYY (ex 22017)
              // M and YYYY -> MM and YYYY
        // calculate relative to current date as months
        for(int i=1;i<numOfRecords;i++){
            // I am simply going to get the last column from record
            String row = input.get(i);
            StringBuilder res = new StringBuilder(row);
            String [] entries = row.split(sep);
            int length = entries.length;
            if(length>0){
                res.append(sep);
                String rec = entries[length-1];
                int expMonth = 0;
                // Case of MYYYY. Assumption is it's either MYYYY or MMYYYY
                if(rec.length()==5){
                    expMonth = Integer.valueOf(rec.substring(0, 1));
                } else {
                    expMonth = Integer.valueOf(rec.substring(0, 2));
                }

                int monToExp = expMonth - currMonth;
                // if calculated > 3
                if(monToExp > 3){
                    res.append(defaultTillExpMonth);
                } else {
                    res.append(monToExp);
                }
                output.add(res.toString());
            }
        }
        // Write into the same file.
        // First We'll delete everything in the input file and then write the modified records

        p = new PrintWriter(new FileWriter("output.txt",false));
        // Ouch. Very bad way to handle resources. You should find a better way
        p.print("");
        p.close();
        // Write into file
        p = new PrintWriter(new FileWriter("InputFile"));
        for(String row : output)
        {
            p.println(row);
        }



    } else {
        System.out.println("No records to process");
    }



    } catch(IOException e){
        e.printStackTrace();
    } finally { // Close file
        if(p!=null){
            p.close();
        }
        if(bufferedReader!=null){
            try {
                bufferedReader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

我强烈建议您了解文件资源是什么，如何有效地处理它们并改进此代码。稍后您应该转到Apache Commons Library

Answer 2

我还没有测试过，但下面的代码应该可以解决你的问题。

List<String> input = FileUtils.readLines(new File("SomeFile"), StandardCharsets.UTF_8);
    List<String> output = new ArrayList<String>();
    if(input.size()>1){
        Calendar cal = Calendar.getInstance();
        cal.setTime(new Date());
        int month = cal.get(Calendar.MONTH) + 1;
        String header = input.get(0) + ",monthsTill";
        output.add(header);
        int length = input.size();
        for(int i=1;i<length;i++){
            StringBuilder str = new StringBuilder();
            String row = input.get(i);
            String [] elements = row.split(",");
            if(elements.length == 2){
             // You have access to both the index and expiry date. So if you want to skip some row, simply don't add it to the ouput collection
                int exp = Integer.parseInt(elements[1].substring(0, 2));
                int monRemaining = month-exp;
                str.append(row).append(",").append(monRemaining);
                output.add(str.toString());
            } else {
                throw new IllegalArgumentException();
            }
        }

        FileUtils.writeLines(new File("SomeFile"), output, false);

请注意，'FileUtils'类来自APache Commons IO包

编辑：如果您不想使用FileUtils，请替换

List<String> input = FileUtils.readLines(new File("SomeFile"), StandardCharsets.UTF_8);

带

List<String> input = new ArrayList<String>();
       File inputFile = new File("SomeFile");
       BufferedReader bufferedReader = new BufferedReader(new FileReader(inputFile));
       String readLine = "";
       while ((readLine = bufferedReader.readLine()) != null) {
           input.add(readLine);
       }

和

 FileUtils.writeLines(new File("SomeFile"), output, false);

与

PrintWriter f0 = new PrintWriter(new FileWriter("SomeFile",false));
        f0.print("");
        // Erase the contents of the input file in a
        // Very bad way
        f0.close();
        f0 = new PrintWriter(new FileWriter("output.txt"));
        for(String row : output)
        {
            f0.println(row);
        }
        f0.close();

当然，如果你不使用Apache Commons IO，你将不得不自己处理像流等关闭资源。

Answer 3

这是我正在尝试做的一些伪代码

    // read csv file
        // append timeTillExpired to end of first row of CSV
        // for each row after first row
            // calculate timeTillExpired
                // if format MYYYY (ex 22017)
                    // M and YYYY
                    // calculate relative to current date as months
                //else
                    // MM and YYYY (ex 122017)
                    // calculate relative to current date as months
            // if calculated > 3
                // timeTillExpired = ">3"
                // add timeTillExpired to end of row
            //else
                // add timeTillExpired to end of row
    // save file
    // close file

Answer 4

这是我计算时间的函数

private static int calculateTimeTill(int date) 
{
    // TODO Auto-generated method stub
    String numberAsString = Integer.toString(date);
    if(numberAsString.length() == 5)
    {
        //format 22017
        String month = numberAsString.substring(0,1);
        String year = numberAsString.substring(1,5);
        int monthResult = Integer.parseInt(month);
        int yearResult = Integer.parseInt(year);
        int day = 1;
        // using Joda - Time http://joda-time.sourceforge.net/installation.html
        // downloaded Joda - Convert as well
        LocalDate expDate = new LocalDate(yearResult, monthResult, day);
        LocalDate currDate = new LocalDate();
        int output = Months.monthsBetween(expDate, currDate).getMonths();
        return output;
    }
    else
    {
        //format 122017
        String month = numberAsString.substring(0,2);
        String year = numberAsString.substring(2,6);
        int monthResult = Integer.parseInt(month);
        int yearResult = Integer.parseInt(year);
        int day = 1;
        // using Joda - Time http://joda-time.sourceforge.net/installation.html
        // downloaded Joda - Convert as well
        LocalDate expDate = new LocalDate(yearResult, monthResult, day);
        LocalDate currDate = new LocalDate();
        int output = Months.monthsBetween(expDate, currDate).getMonths();
        return output;
    }
}

Java将带计算的列添加到CSV文件

4 个答案: