It is simple to redirect a process output to a standard file using the '>' operator.
But if you also want the std error to go to a file, then you need to type:
java className>file 2>&1
To understand what the above command means, it is imp to note that the shell reads arguments from left to right. The shell sees >file first and redirects stdout to file. Next 2>&1 sends fd2 (stderr) to the same place fd1 is going - that's to the file.