Hook into System.out.println(); and modify

Question

I would like to modify the output printed by System.out.println();. How is this possible? It is possible - I've seen it in Bukkit/Craftbukkit. If a plugin is printing a string with System.out.println(String string); Bukkit adds a time/date and logging status to the string. I would like to do the same like Bukkit.

Answer 1

You can change the PrintStream that is used as the standard output:

System.setOut(PrintStream out)

Create your own PrintStream implementation which prints whatever extra info you want to the (old) standard output, and set it with:

System.setOut(myStream);

Example:

The following example prints the current time millis before each printed String that is printed with PrintStream.println(String x) method:

PrintStream myStream = new PrintStream(System.out) {
    @Override
    public void println(String x) {
        super.println(System.currentTimeMillis() + ": " + x);
    }
};
System.setOut(myStream);
System.out.println("Hello World!");

Output:

1420553422337: Hello World!

Note:

This example only overrides the PrintStream.println(String x) method, so calling other print methods of PrintStream would not add the time stamp to the output.