How to overwrite a line from a TXT file in Java?

Question

How to overwrite a line from a TXT file in Java?

For example, if I have a file with the following text:

User_1, password_1, Active

User_2, password_2, Active

User_3, password_3, Active

And I want to change it to look like this:

User_1, password_1, not Active

User_2, password_2, Active

User_3, password_3, Active

I just want to overwrite Line 1 of that file. Have tried with the FileWriter, however, with that library I can only write one line at the end, so it would remain:

User_1, password_1, Active

User_2, password_2, Active

User_3, password_3, Active

User_1, password_1, not Active

I have also tried creating another file in which I am changing lines from the current file and adding them to the new file, to finally delete the previous file. It works, however I do not think it is the most optimal.

1

Author: Eslacuare, 2016-10-23

Source

2 answers

score 1 · Answer 1

You can send as a parameter the line position you want to overwrite to the input method, if also the modified line. try this:.

import java.io.File;
import java.io.FileReader;

import javax.swing.JOptionPane;

public class Archivo {
String ruta;
public Archivo() {

}

public Archivo(String ruta){
    this.ruta = ruta;
    try {
        File archivo = new File(this.ruta);
        this.ruta = archivo.getCanonicalPath();
    } catch (Exception e) {

    }
}

public String leerArchivo(){
    String cadena = "";
    FileReader entrada = null;
    try {
        entrada = new FileReader(ruta);
        int c;
        while((c = entrada.read()) != -1){
            cadena += (char)c;
        }
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, "Error al leer archivo: "+e.getMessage());
    }
    return cadena;
}

public void ingresar(String nuevaLinea, int posicion){
    FileWriter fichero = null;
    PrintWriter escritor = null;
    try {
        fichero = new FileWriter(ruta);
        escritor = new PrintWriter(fichero);
        escritor.flush();
        String split[] = leerArchivo().split("\n");
        split[posicion] = nuevaLinea;
        for(int x = 0; x < split.length; x++){
            escritor.write(split[x]);
            escritor.println();
         }
        escritor.close();
    } catch (IOException e) {
        JOptionPane.showMessageDialog(null, "Error al escribir en el archivo de texto: "+e.getMessage());
    } finally {
        if(fichero != null){
            try {
                fichero.close();
            } catch (IOException e) {
                JOptionPane.showMessageDialog(null, "Error al cerrar archivo de texto: "+e.getMessage());
            }
        }
    }
}
}

score 0 · Answer 2

With RandomAccessFile you could achieve this, but considering that there are two more characters to write "NO" so for this example you need the line to have 3 more spaces Usuario_1,contrasena_1,Activo___ (_) spaces to then do something with this

/* RW , para Lectura(Read) y Escritura (Writer) */
RandomAccessFile archivo = new RandomAccessFile("./Archivo.txt", "rw");
/* Posicionar al inicio del archivo, con seek te posicionas en el lugar 
 que desees del archivo */
archivo.seek(0);
/* Escribir la cadena */ 
archivo.writeBytes("Usuario_1,contrasena_1,NO Activo");
archivo.close();/* Cerrar el archivo importante */

The other option is to read the entire file and replace the line word and then rewrite everything again (I prefer RandomAccesFile)

BufferedReader file = new BufferedReader(new FileReader("./Archivo.txt"));
    String line;String input = "";
    while((line = file.readLine()) != null){
        /* Podemos verificar si es Usuario_1 y \r\n es para hacer el 
          Salto de Línea y tener el formato original */
        if(line.contains("Usuario_1"))
            input += line.replaceAll("Activo", "NO Activo \r\n");
        else
            input += line+"\r\n";
    }
    FileOutputStream fileOut = new FileOutputStream("./Archivo.txt");
    fileOut.write(input.getBytes());
    fileOut.close();