Redirect standard error - A Java Code Example

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To redirect standard error (or System.err) there's a method in the System class called setErr() which takes a PrintStream instance as argument.
If we for example want to redirect all messages on System.err to a file, we can create a FileOutputStream instance and send it to the constructor of the PrintStream.
This Java code example creates the FileOutputStream with the filename "standard_err.txt" and pass it to the PrintStream, which in turn is passed to the setErr() method.
A NullPointerException is forced to test that the stacktrace is printed to the file.

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;
/**
* Main.java
*
* @author www.javadb.com
*/
public class Main {

    /**
     * Redirects System.err and sends all data to a file.
     *
     */
    public void redirectSystemErr() {

        try {

            System.setErr(new PrintStream(new FileOutputStream("system_err.txt")));

            String nullString = null;

            //Forcing an exception to have the stacktrace printed on System.err
            nullString = nullString.toUpperCase();

        } catch (FileNotFoundException ex) {
            ex.printStackTrace();
        }
    }
    /**
     * Starts the program
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new Main().redirectSystemErr();
    }
}

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