Writing/Altering csv file java

Question

I am loading a CSV file and kept alive without closing BufferReader. Now I want to add/delete few more rows to my CSV and get updated CSV. Which means I want dynamically notified when CSV file is altered.

Here is my sample code:

public class Check {


    public static void main(String args[]) throws IOException, InterruptedException{
        Check ch = new Check();
        //args[0] = "C:\\Users\\raponnam\\Desktop\\GxDefault.csv";
        String csvFile="C:\\Users\\raponnam\\Desktop\\GxDefault.csv";

        int lineCounter=0;
        if (csvFile!=null)
        {
            BufferedReader csvToRead = null;
            try{
                csvToRead = new BufferedReader(new FileReader(csvFile));
                String line;
                while ((line=csvToRead.readLine())!=null)
                {
                    lineCounter++;
                    String[] splitLine = line.split(",");
                    System.out.println("no of lines-->> "+lineCounter);
                }
                while(true)
                {

                    System.out.println("wait 6 seconds");
                    Thread.sleep(6000);
                }
            }finally{
                //csvToRead.close();
            }
        }
    }
}

take a look if its meaningful : stackoverflow.com/a/15128402/1283215 — Hussain Akhtar Wahid 'Ghouri'
– Hussain Akhtar Wahid 'Ghouri', Commented Nov 6, 2013 at 9:47
Use WatchService of Java and filter out for a specific events. docs.oracle.com/javase/tutorial/essential/io/notification.html stackoverflow.com/questions/16251273/… — Abhijith Nagarajan
– Abhijith Nagarajan, Commented Nov 6, 2013 at 9:52
You could also use Apache Commons IO library commons.apache.org/proper/commons-io/apidocs/org/apache/commons/… — Abhijith Nagarajan
– Abhijith Nagarajan, Commented Nov 6, 2013 at 10:04

rlegendi · Accepted Answer · 2013-11-06 10:15:20Z

1

CSV handling is far more complicated than you would first think.

The issues causing the nightmares are the different column separators, locales (e.g., if you use , for column separators it might fire back with doubles on some locales, since it is used to denote the decimals), columns are sometimes wrapped with special characters (like " or '), escaping comes into the picture, etc.

If you allow me to have an advice, use a mature CSV lib for the task like OpenCSV (but there are tons of alternatives there). It's quite trivial to use, see the linked site for examples.

answered Nov 6, 2013 at 10:15

rlegendi

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Barun · Accepted Answer · 2013-11-06 10:04:42Z

Use this. Have restructured your code. If readLine returns a number after returning nulls, you can assume that something has been added to the csv file.

PS: If file contents are deleted; the code doesnt work.

String csvFile = "C:\\a.csv";

    int lineCounter = 0;
    if (csvFile != null) {
        BufferedReader csvToRead = null;
        try {
            csvToRead = new BufferedReader(new FileReader(csvFile));
            String line;
            while (true) {
                if ((line = csvToRead.readLine()) != null) {
                    lineCounter++;
                    String[] splitLine = line.split(",");
                    System.out.println("no of lines-->> " + lineCounter);
                }
                System.out.println("wait 6 seconds");
                Thread.sleep(6000);
            }
        } finally {
            // csvToRead.close();
        }
    }

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