Question

I log my app errors. but if the logging process failed for some reasons ( database error , no space in the hard disk .. etc ) . how can I know that ? How to log the failed log.

example :

try{

    this_will_throw_exception();

}catch(Exception e){

    result = Log.error(e.getMessage());
    if( result == false)
        {
         // what should I do ?
        }
}

Answer 1

You should keep your application code simple, i.e. not to worry about logging failure and delegate the logging failure to the logger itself.

Hence your application code should look like:

try{
  this_will_throw_exception();
} catch(Exception e){
  Log.error(e.getMessage());
}

Now we look at how to handle failure in logger.

First, there is a lot of logging framework that provide appender failover. For example there us a FailoverAppender in log4j that log to secondary appender if the primary failed. http://logging.apache.org/log4j/2.x/manual/appenders.html

If you choose to build your own logging layer for whatever reason, you may find the decorator pattern useful to build failover logger yourself.

public interface Logger {
  boolean error(String message);
}

public DataBaseLogger implements Logger {
  ...
}

public FileLogger implements Logger {
  ...
}

public FailoverLogger implements Logger {
  private Logger primary;
  private Logger secondary;

  public boolean error(String message) {
    boolean succeed = primary.error(message);
    if (! succeed) {
      secondary.error("Primary logger failed");
      secondary.error(message);
      // Try to restart the primary logger, however it might be difficult.
    }
  }
}