CODEWITHSUNDEEP
javacsv
Chognificent
Chognificent

Reputation: 413

Add/append data to specific row/cell of an existing CSV file

I'm trying to append a value to a specific row in a csv file but append'd default is to add the value at the end of the csv file. Not exactly sure how to tell it to append at the end of a specific row. My code looks like the following: 

try {
        writer = new FileWriter(csvFile ,true);
        br = new BufferedReader(new FileReader(csvFile));
        while ((line = br.readLine()) != null) {

            // use comma as separator
            String[] id = line.split(cvsSplitBy);

            if(id[0].equals("1")){
                writer.append(",");
                writer.append("Success");
                System.out.println("Done");
            }
        }

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (br != null) {
            try {
                br.close();
                writer.flush();
                writer.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

The goal is to make the program add "success" where the csv row id is equal to 1. Current result is:

Id,Name,Sex,Age
1,Nick,Male,23
2,Dick,Male,25,Success

What I would like is:

Id,Name,Sex,Age
1,Nick,Male,23,Success
2,Dick,Male,25

Any help would be appreciated. Thanks.

Upvotes: 0

Views: 4583

Answers (3)

Manas Kumar Maharana
Manas Kumar Maharana

Reputation: 935

Yes, you can achieve this but not straight forward .... you need to read and append your data at beginning then write as new file, this will override .

Find below example:
1 - Read file, keep header to separate then content to separate
2 - add you new content/row data to list of beginning
3 - add header to beginning as we want header should be first
4 - then write whole data to .csv file
Code(You need add jar/dependency in pom for CSVWritter/CSVReader) -

   try {
        FileReader filereader = new FileReader(file);

        CSVReader csvReader = new CSVReaderBuilder(filereader).build();
        String[] header = csvReader.readNext();
        List<String[]> allData = csvReader.readAll();
        FileWriter outputfile = new FileWriter(file, false);
        CSVWriter writer = new CSVWriter(outputfile);

        String[] data = {"test1", "test2"};
        allData.add(0,data);
        allData.add(0,header);
        for (String[] dt : allData){
            writer.writeNext(dt);
        }
        // closing writer connection
        writer.close();
    }
    catch (Exception e) {
        e.printStackTrace();
    }

Enjoy :)

Upvotes: 0

Klitos Kyriacou
Klitos Kyriacou

Reputation: 11621

You can't just append to the end of a line and expect the following lines to stay where they are. Think about the structure of a text file, e.g. one containing the following lines:

one
two

This file is contains the following sequence of characters:

"o", "n", "e", "\n", "t", "w", "o", "\n"

Now, if you add more characters at the end of line 1, you will overwrite line 2.

Therefore, when you insert characters at the end of a line, you need to shift the remainder of the file to make space. That means you have to copy the contents of the remainder of the file, write your ", Success" string, then copy the saved characters back to the file.

But you're creating a FileWriter with the append flag set to true. That means every write appends to the end of the file. What you need to do, instead of appending, is mark the position where you need to write, and start writing at that position. Perhaps the easiest class for doing this is RandomAccessFile.

Upvotes: 1

Victor P
Victor P

Reputation: 1612

Since CSV rows are terminated by a CRLF (or just LF), you can just read the entire contents of the file into a string and use a regular expression to replace CRLF with successCRLF.

The regular expression would be something like this:

1.*(\r\n)

Giving you \r\n as a numbered capture group.

Hope this helps

Upvotes: 0

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