How to append character to a file certain "string" in java

Question

File filename =new File("D:/text.txt");

final Scanner scanner = new Scanner(filename);
while (scanner.hasNextLine()) {
    final String lineFromFile = scanner.nextLine();

    if(lineFromFile.contains("-----END CERTIFICATE REQUEST-----") ) { 
        FileWriter fw = new FileWriter(filename,true); //the true will append the new data

        fw.append(",");
        fw.write("wirte123");//appends the string to the file
        fw.close();

        System.out.println("I found "  +filename.getName());
        break;
     }
}

but for me it is adding after a new line....as shown below

Need the output file as below

Your file already contains that line break character. To get your desired result you'd have to remove that one first and then append your string — reto, Jun 24 '16 at 08:12
probably the new line char is already in original file (edit: as he said) — Zeromus, Jun 24 '16 at 08:13
Can you guys please suggest me ,how to break the new line char ..? — String, Jun 24 '16 at 08:15
@String Get content of whole file and then check the last char and if '\n' or '\r\n' then replace to empty string. After that you can append your content. — Krzysiek, Jun 24 '16 at 08:18
Take a look here: http://stackoverflow.com/questions/7454330/how-to-remove-newlines-from-beginning-and-end-of-a-string-java — Mistalis, Jun 24 '16 at 08:32

score 2 · Answer 1 · answered Jun 24 '16 at 09:40

The original file already contains an ending new line. So if you append something to the original file, it will be written after that new line.

What is worse, is that a Scanner is a high level object that do not allow you to know the exact position in the file where an internal cursor could be positionned, because internally it reads large buffers (for a certificate file, the whole file is likely to be read at once).

So you should rather use a RandomAccessFile and its associated FileChannel to record the position of each begin of line, and to truncate the file just before a possible end of line.

Code could become:

    RandomAccessFile fw = new RandomAccessFile(filename, "rw");
    FileChannel fc = fw.getChannel();
    long oldpos;
    while (true) {
        oldpos = fc.position();
        final String lineFromFile = fw.readLine();

        if (lineFromFile.contains("-----END CERTIFICATE REQUEST-----")) {
            System.out.println("I found "  +filename.getName());*/
            fc.truncate(oldpos + lineFromFile.length());
            fw.writeBytes(",wirte123");//appends the string to the file
            break;
        }
    }
    fw.close();

Piyush Aghera · Answer 2 · 2016-06-25T15:38:02.567

0

You can use Bufferwriter with fileWriter and use append method of buffer writer and it will append to text instead of creating new line.

E.g.

 File filename = new File("D:/text.txt");
 FileWriter fileWritter = new FileWriter(filename,true);
 BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
 bufferWritter.append(",wirte123");
 bufferWritter.close();
 fileWritter.close();

edited Jun 25 '16 at 15:38

answered Jun 24 '16 at 09:13

Piyush Aghera

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How to append character to a file certain "string" in java

2 Answers2