Redirect System.out.println statements to a stream or file

'java.lang.System' class provides setOut, setErr methods to redirect system output and error messages.

Redirect out stream messages to debug.log file

PrintStream outStream = new PrintStream(new FileOutputStream("/Users/krishna/Documents/debug.log", true));

System.setOut(outStream);

Redirect err stream messages to error.log file

PrintStream errStream = new PrintStream(new FileOutputStream("/Users/krishna/Documents/error.log", true));

System.setErr(errStream);

App.java

package com.sample.app;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;

public class App {

 public static void main(String args[]) throws FileNotFoundException {
  PrintStream outStream = new PrintStream(
    new FileOutputStream("/Users/krishna/Documents/debug.log", true));
  PrintStream errStream = new PrintStream(
    new FileOutputStream("/Users/krishna/Documents/error.log", true));

  System.setOut(outStream);
  System.setErr(errStream);

  System.out.println("Starting the application");
  System.err.println("Error Occurred while executing the application");
  System.out.println("Exiting the application");

 }
}

Run App.java

Open debug.log, you can see below messages.

Starting the application

Exiting the application

Open error.log, you can see below messages.

Error Occurred while executing the application

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