In Java, how can I redirect System.out to null then back to stdout again?

Question

I've tried to temporarily redirect System.out to /dev/null using the following code but it doesn't work.

System.out.println("this should go to stdout");

PrintStream original = System.out;
System.setOut(new PrintStream(new FileOutputStream("/dev/null")));
System.out.println("this should go to /dev/null");

System.setOut(original);
System.out.println("this should go to stdout"); // This is not getting printed!!!

Anyone have any ideas?

Answer 1

Man, this is not so good, because Java is cross-platform and '/dev/null' is Unix specific (apparently there is an alternative on Windows, read the comments). So your best option is to create a custom OutputStream to disable output.

try {     System.out.println("this should go to stdout");      PrintStream original = System.out;     System.setOut(new PrintStream(new OutputStream() {                 public void write(int b) {                     //DO NOTHING                 }             }));     System.out.println("this should go to /dev/null, but it doesn't because it's not supported on other platforms");      System.setOut(original);     System.out.println("this should go to stdout"); } catch (Exception e) {     e.printStackTrace(); } 

Answer 2

You can use the class NullPrintStream below as:

PrintStream original = System.out; System.setOut(new NullPrintStream()); System.out.println("Message not shown."); System.setOut(original); 

And the class NullPrintStream is...

import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.OutputStream; import java.io.PrintStream;  public class NullPrintStream extends PrintStream {    public NullPrintStream() {     super(new NullByteArrayOutputStream());   }    private static class NullByteArrayOutputStream extends ByteArrayOutputStream {      @Override     public void write(int b) {       // do nothing     }      @Override     public void write(byte[] b, int off, int len) {       // do nothing     }      @Override     public void writeTo(OutputStream out) throws IOException {       // do nothing     }    }  } 

Answer 3

Since JDK 11 there is OutputStream.nullOutputStream(). It does exactly what you are looking for:

System.setOut(new PrintStream(OutputStream.nullOutputStream());