Thread: Saving new value to file

hello,

I'm having issues with writing changed value to a file. In my file I have a string which contains

Fri Jan 14 15:00:00 CET 1898feeffeg

I want to change one field foe example I want to replace 15:00 to 18:00 but when I run my code it deletes all the contents and writes in only the new value. But I want to keep the original content and only replace one field.

Can you please help me to detect th error in my code? Thank you very much

    }
        File file = new File("D:\\...\\events\\" + id + ".events.txt");
 
 
 
 
        try {
            BufferedReader bufferedReader = null;
            FileInputStream fileInputStream = null;
            InputStreamReader inputStreamReader =null;
 
            try {
                fileInputStream = new FileInputStream(file);
                inputStreamReader = new InputStreamReader(fileInputStream);
                bufferedReader = new BufferedReader(inputStreamReader);
 
            } catch (FileNotFoundException e) {
                e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
            }
 
            System.out.println("Searching for :" + Changefield + " in file: " + file.getName());
 
 
            while((field = bufferedReader.readLine()) != null) {
                int index = field.indexOf(Changefield);
 
                 System.out.println("Position of " + Changefield + "is at the position: " + index);
                 System.out.println(Changefield.replaceFirst(Changefield, newValue));
                 System.out.println("Old value " + Changefield + " new value : " + newValue);
 
 
            }
            Path from = Paths.get(String.valueOf(file));
            Path to = Paths.get("D:\\...\\events\\" + id + ".events-Temp.txt");
            CopyOption[] option = new CopyOption[]{
                    StandardCopyOption.REPLACE_EXISTING,
                    StandardCopyOption.COPY_ATTRIBUTES
            };
            for (Path path : Files.copy(from, to, option)) {
 
            }
            try{
                FileWriter fileWriter1 = new FileWriter(file);
                writer = new BufferedWriter(fileWriter1);
                writer.write(newValue);
 
            //    writer.flush();
 
        }catch(Exception e){
            System.err.println("Error: " +e.getMessage());
        }finally {
            try{
                writer.close();
            }catch(IOException e){
                System.err.println("Error " + e.getMessage());
            }
        }
 
 
        } catch (IOException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        }
    }

Investigate (search) how to open the file or the mechanism that writes to it by appending data rather than writing to it replacing the existing data.

It occurred to me after reading Norm's message that you may not have explained the problem thoroughly. If you want to intersperse new data with old data in the lines of the file, like:

OLD
new
OLD
new
OLD
new
. . . etc.

Then you'll have to use either of the approaches Norm suggested.

Can you please help me out with it? I'm really lost

I need sth like this : OLD variable,new variable, OLD, Old

And there's only one line of data in the whole file?

Yes,only one with 5 variables nd I want to change only 1

That's trivial. Read the line, change the data in the line, write the line back to the file. No appending or any other tricks are required. Try printing (to the screen) the line as it is read from the file and then after your program has changed it. Work that until what is being printed to the screen after it is changed contains the updated data. Then write that string to the file.

Look into the method String.split() to break the line of data into its parts so that you can easily find and change the correct item, then reconstruct the line of data from the original array with the new data substituted in for the old.