code: public static void install() {
          synchronized (log()) {
              if (!cInstalled) {
                  cInstalled = true;
                  cOriginalOut = System.out;
                  cOriginalErr = System.err;
                  
                  cSystemOut = new LogEventParsingOutputStream
                      (log(), LogEvent.INFO_TYPE) 
                  {
                      public boolean isEnabled() {
                          return log().isInfoEnabled();
                      }
                  };
                  cSystemOut.addLogListener(log());
                  System.setOut(new PrintStream(cSystemOut, true));
  
                  cSystemErr = new LogEventParsingOutputStream
                      (log(), LogEvent.ERROR_TYPE) 
                  {
                      public boolean isEnabled() {
                          return log().isErrorEnabled();
                      }
                  };
                  cSystemErr.addLogListener(log());
                  System.setErr(new PrintStream(cSystemErr, true));
              }
          }
      }
docs: When installed, System.out and System.err are redirected to Syslog.log.
  System.out produces info events, and System.err produces error events.