updating specific cell csv file using java

Question

Hi i have a small problem and think i'm just not getting the correct syntax on one line of code. basically, i can write into my csv file and find a specific record using string tokenizer but it is not updating/editing the specified cells of that record. the record remains the same. please help....

We have absolutely no clue what you're doing, so we can't tell what part you're doing wrong... — Ignacio Vazquez-Abrams, Dec 09 '10 at 11:56
Do you mean it isn't updating your file? The question would be a lot easier to anwer if you provided a short example of what you are trying to do and information about how it fails. — Mattias Nilsson, Dec 09 '10 at 12:02
also, if you need to work with csv files, did you have a look at any of the available csv packages for Java? If you're doing something non-trivial, they might make your life easier. — Mattias Nilsson, Dec 09 '10 at 12:02

score 7 · Answer 1 · answered Sep 25 '15 at 13:09

I have used http://opencsv.sourceforge.net in java

Hi, This is the code to update CSV by specifying row and column

/**
 * Update CSV by row and column
 * 
 * @param fileToUpdate CSV file path to update e.g. D:\\chetan\\test.csv
 * @param replace Replacement for your cell value
 * @param row Row for which need to update 
 * @param col Column for which you need to update
 * @throws IOException
 */
public static void updateCSV(String fileToUpdate, String replace,
    int row, int col) throws IOException {

File inputFile = new File(fileToUpdate);

// Read existing file 
CSVReader reader = new CSVReader(new FileReader(inputFile), ',');
List<String[]> csvBody = reader.readAll();
// get CSV row column  and replace with by using row and column
csvBody.get(row)[col] = replace;
reader.close();

// Write to CSV file which is open
CSVWriter writer = new CSVWriter(new FileWriter(inputFile), ',');
writer.writeAll(csvBody);
writer.flush();
writer.close();
}

This solution worked for me, Cheers!

score 5 · Answer 2 · answered Dec 05 '17 at 17:37

I used the below code where I will replace a string with another and it worked exactly the way I needed:

public static void updateCSV(String fileToUpdate) throws IOException {
        File inputFile = new File(fileToUpdate);

        // Read existing file
        CSVReader reader = new CSVReader(new FileReader(inputFile), ',');
        List<String[]> csvBody = reader.readAll();
        // get CSV row column and replace with by using row and column
        for(int i=0; i<csvBody.size(); i++){
            String[] strArray = csvBody.get(i);
            for(int j=0; j<strArray.length; j++){
                if(strArray[j].equalsIgnoreCase("Update_date")){ //String to be replaced
                    csvBody.get(i)[j] = "Updated_date"; //Target replacement
                }
            }
        }
        reader.close();

        // Write to CSV file which is open
        CSVWriter writer = new CSVWriter(new FileWriter(inputFile), ',');
        writer.writeAll(csvBody);
        writer.flush();
        writer.close();
    }

lifesaver! I knew this is what I needed to do, I had trouble on how to update the cell and write successfully, but this filled the gaps and holes in my logic. thank you! — frlzjosh, May 31 '20 at 01:54

score 1 · Answer 3 · edited May 23 '17 at 11:59

You're doing something like this:

  String line = readLineFromFile();
  line.replace(...);

This is not editing the file, it's creating a new string from a line in the file.

String instances are immutable, so the replace call you're making returns a new string it does not modify the original string.

Either use a file stream that allows you to both read and write to the file - i.e. RandomAccessFile or (more simply) write to a new file then replace the old file with the new one

In psuedo code:

for (String line : inputFile) {
    String [] processedLine = processLine(line);
    outputFile.writeLine(join(processedLine, ","));
}

private String[] processLine(String line) {
    String [] cells = line.split(","); // note this is not sufficient for correct csv parsing.
    for (int i = 0; i < cells.length; i++) {
        if (wantToEditCell(cells[i])) {
           cells[i] = "new cell value";
        }
    }

    return cells;
}

Also, please take a look at this question. There are libraries to help you deal with csv.

not sure how to implement the RAF and have done a bit of reading on it any way to point me in the right direction by code? — JavaBabyGirl, Dec 09 '10 at 14:24

score -1 · Answer 4 · edited Jun 20 '20 at 09:12

CSV file is just a file. It is not being changed if you are reading it. So, write your changes!

You have 3 ways.

1

read line by line finding the cell you want to change.
change the cell if needed and composite new version of current line.
write the line into second file.
when you finished you have the source file and the result file. Now if you want you can remove the source file and rename the result file to source.

2

Use RandomAccess file to write into specific place of the file.

3

Use one of available implementations of CSV parser (e.g. http://commons.apache.org/sandbox/csv/) It already supports what you need and exposes high level API.

updating specific cell csv file using java

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