How to replace specific String in a text file by java?

Question

I'm writing a program with a text file in java, what I need to do is to modify the specific string in the file. For example, the file has a line(the file contains many lines)like "username,password,e,d,b,c,a" And I want to modify it to "username,password,f,e,d,b,c" I have searched much but found nothing. How to deal with that?

Answer 1

In general you can do it in 3 steps:

1. Read file and store it in String
2. Change the String as you need (your "username,password..." modification)
3. Write the String to a file

You can search for instruction of every step at Stackoverflow.

Here is a possible solution working directly on the Stream:

public static void main(String[] args) throws IOException {

    String inputFile = "C:\\Users\\geheim\\Desktop\\lines.txt";
    String outputFile = "C:\\Users\\geheim\\Desktop\\lines_new.txt";

    try (Stream<String> stream = Files.lines(Paths.get(inputFile));
            FileOutputStream fop = new FileOutputStream(new File(outputFile))) {
        stream.map(line -> line += " manipulate line as required\n").forEach(line -> {
            try {
                fop.write(line.getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
    }
}