Redirecting java Standard output and standard error to file

It is useful to redirect standard java output to a file. However, if you are wondering why your stacktrace from e.printStackTrace() is not being redirected to a file then read on…

Say you have a program called RedirectExample.java. To redirect the output to a text file do

java RedirectExample > output.txt

However, if your code in RedirectExample.java throws an exception which you want to print via e.printStackTrace(), you wont be able to see that in output.txt. The reason is that e.printStackTrace() writes to the error stream (System.err) and the statement above does redirects only the output stream (System.out) to output.txt and not the error stream.

To redirect error stream use the following command

java RedirectExample > output.txt 2>&1

This redirects the error stream(2) to outputstream(1), which in turn is redirected to the text file.

Here’s RedirectExample.Java

 
public class RedirectExample { 
   public static void main(String[] args) { 
         System.out.println("From System Out"); 
         try { 
                 String a = null; 
                 a.toString(); 
             } catch (Exception e) { 
               e.printStackTrace(); 
             } 
    } 
}