Question

There is a pattern that happens every now and then. I have a method called many times, and it contains this snippet:

Foo foo = getConfiguredFoo();
if (foo == null) {
  logger.warn("Foo not configured");
  foo = getDefaultFoo();
}

Then my log file is cluttered with this warning a hundred times. I know I can grep it out, but I wonder if there is a better way to see this warning only once.

Note: the duplication of messages is a correct behavior by default, so this is not about avoiding unintentional duplicate log message. I tagged my question as log4j, but I’m open to other java logging frameworks.

Answer 1

Here is what I can come up with: a class that accumulates warnings which can be dumped at the end. It’s in groovy, but you can get the point. The dumping part can be customized to use a logger, of course.

class BadNews {
  static Map<String,List<Object>> warnings = [:];

  static void warn(String key, Object uniqueStuff) {
    def knownWarnings = warnings[key]
    if (! knownWarnings) {
      knownWarnings = []
      warnings[key] = knownWarnings
    }
    knownWarnings << uniqueStuff
  }

  static void dumpWarnings(PrintStream out) {
    warnings.each{key, stuffs ->
      out.println("$key: " + stuffs.size())
      stuffs.each{
        out.println("\t$it")
      }
    }
  }
}

class SomewhereElse {
  def foo(Bar bar) {
    if (! bar)
      BadNews.warn("Empty bar", this)
  }
}