Redirect System.out.println to log

Question

In my project test suite there is big usage of

System.out.println 

I\'m trying to redirect these output to log file (through configuration

Answer 1

Given that it's better replace the System.out.println(), sometimes we have no choice. Anyway I've made a little utility for that:

SystemOutToSlf4j.enableForClass(MyClass.class)

Then all the println originated from MyClass will be redirected to the logger. See this post for more details...

public class SystemOutToSlf4j extends PrintStream {

  private static final PrintStream originalSystemOut = System.out;
  private static SystemOutToSlf4j systemOutToLogger;

  /**
   * Enable forwarding System.out.println calls to the logger if the stacktrace contains the class parameter
   * @param clazz
   */
  public static void enableForClass(Class clazz) {
    systemOutToLogger = new SystemOutToSlf4j(originalSystemOut, clazz.getName());
    System.setOut(systemOutToLogger);
  }


  /**
   * Enable forwarding System.out.println calls to the logger if the stacktrace contains the package parameter
   * @param packageToLog
   */
  public static void enableForPackage(String packageToLog) {
    systemOutToLogger = new SystemOutToSlf4j(originalSystemOut, packageToLog);
    System.setOut(systemOutToLogger);
  }

  /**
   * Disable forwarding to the logger resetting the standard output to the console
   */
  public static void disable() {
    System.setOut(originalSystemOut);
    systemOutToLogger = null;
  }

  private String packageOrClassToLog;

  private SystemOutToSlf4j(PrintStream original, String packageOrClassToLog) {
    super(original);
    this.packageOrClassToLog = packageOrClassToLog;
  }

  @Override
  public void println(String line) {
    StackTraceElement[] stack = Thread.currentThread().getStackTrace();
    StackTraceElement caller = findCallerToLog(stack);
    if (caller == null) {
      super.println(line);
      return;
    }

    org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(caller.getClass());
    log.info(line);
  }

  public StackTraceElement findCallerToLog(StackTraceElement[] stack) {
    for (StackTraceElement element : stack) {
      if (element.getClassName().startsWith(packageOrClassToLog))
        return element;
    }

    return null;
  }

}