Find and replace words in a text file using Java

Question

I am trying to find and replace certain words in a text file using Java. My code works to an extent however the output that I am getting is wrong. I need to replace multiple words from a line in a text file with user input. However, when I run my code the line copies itself once for every word I am trying to replace.

For example if I want to replace 3 words from the following:

python ycsb phase db -s -P /home/james/YCSB/workloads/workloada -p 
db.url=db://IP:port -p db.database=name

I end up with 3 copies of the line, each with a different word replaced. Rather than 1 line with all 3 of the required words replaced. Code provided below, thanks in advance.

public static void main(String[] args) {

    System.out.print("Phase: ");
    Scanner sp = new Scanner(System.in);
    String p = sp.nextLine();
    
    System.out.print("Database: ");
    Scanner sd = new Scanner(System.in);
    String d = sd.nextLine();
    
    System.out.print("IP address: ");
    Scanner sip = new Scanner(System.in);
    int ip = sip.nextInt();
     
    try {
        File file = new File("C://users//James//Desktop//newcommand.txt");
        BufferedReader reader = new BufferedReader(new FileReader(file));
        String line = "", oldtext = "";
        while((line = reader.readLine()) != null) {
            oldtext += line + "\r\n";
        }
        reader.close();
       
        String phase  = oldtext.replaceAll("phase", "" + p);
        String database = oldtext.replaceAll("db", "" + d);
        String ips = oldtext.replaceAll("IP", "" + ip);
        
        FileWriter writer = new FileWriter("C://users//James//Desktop//newcommand.txt");
        writer.write(phase + ips + database);
        writer.close();
    } catch (IOException e) {
        // handle e
    }
}

Answer 1

if I understand well the situation, maybe the problem is that you are replacing the same string,and storing in different var,

try that:

  public static void main(String[] args) {
        System.out.print("Phase: ");
        Scanner sp = new Scanner(System.in);
        String p;
        p = sp.nextLine();

        System.out.print("Database: ");
        Scanner sd = new Scanner(System.in);
        String d;
        d = sd.nextLine();

        System.out.print("IP address: ");
        Scanner sip = new Scanner(System.in);
        int ip = sip.nextInt();

        {
         try
             {
             File file = new File("C://users//James//Desktop//newcommand.txt");
             BufferedReader reader = new BufferedReader(new FileReader(file));
             String line = "", oldtext = "";
             while((line = reader.readLine()) != null)
                 {
                 oldtext += line + "\r\n";
             }
             reader.close();

             String replacedtext  = oldtext.replaceAll("phase", "" + p);
             replacedtext = replacedtext.replaceAll("db", "" + d);
             replacedtext = replacedtext.replaceAll("IP", "" + ip);

             FileWriter writer = new FileWriter("C://users//James//Desktop//newcommand.txt");
             writer.write(replacedtext);


             writer.close();

         }
         catch (IOException ioe)
             {
             ioe.printStackTrace();
         }
     }

Answer 2

Better version of existing answers:

public static void main(String[] args)
{
    Scanner sp = new Scanner(System.in);
    System.out.print("Phase: ");
    String pstr = s.nextLine();
    System.out.print("Database: ");
    String dstr = s.nextLine();
    System.out.print("IP address: ");
    String ipstr = String.valueOf(s.nextInt());

After reading the input we can use two efficient methods to read from the file, and write back. First I suggest writing to a temporary file (this is how sed replaces text in a file too). An advantage of this method is that the final move is probably going to be an atomic operation.

    File f = new File("C://users//James//Desktop//newcommand.txt");
    File ftmp = new File("C://users//James//Desktop//~tmp.newcommand.txt", ".txt");
    try
    {
        BufferedReader br = new BufferedReader(new FileReader(f));
        BufferedWriter bw = new BufferedWriter(new FileWriter(ftmp));
        String ln;
        while((ln = br.readLine()) != null)
        {
            bw.write(ln
                .replace("phase", pstr)
                .replace("db", dstr)
                .replace("IP", ipstr)
            );
            bw.newLine();
        }
        br.close();
        bw.close();
        Files.move(ftmp.toPath(), f.toPath(), StandardCopyOption.REPLACE_EXISTING);
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }

Or if you really don't want to have a temporary file, and thus keep everything in RAM, then use this code:

    File f = new File("C://users//James//Desktop//newcommand.txt");
    try
    {
        String ENDL = System.getProperty("line.separator");

        StringBuilder sb = new StringBuilder();

        BufferedReader br = new BufferedReader(new FileReader(f));
        String ln;
        while((ln = br.readLine()) != null)
        {
            sb.append(ln
                .replace("phase", pstr)
                .replace("db", dstr)
                .replace("IP", ipstr)
            ).append(ENDL);
        }
        br.close();

        BufferedWriter bw = new BufferedWriter(new FileWriter(f));
        bw.write(sb.toString());
        bw.close();
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }

Don't forget the closing bracket ;)

}

Note that - in contrary to the other answers - I am using .replace instead of .replaceAll. The only difference is that the latter interprets the first argument as a regular expression instead of a literal string. Both replace all occurrences, in this case there's no need for regular expressions and might only result in unwanted behavior due to special characters.