Question

I am using Log4j as logging framework in a project I am working on. I have the following situation: Log4j is configured to write the logs into a log file. At some point, this log file is copied to another destination and deleted. Logging framework keeps working, but the logs are not written to the log file because it is deleted. Is there any way to tell Log4j to recreate the file and keep writing the logs into the log file.

Best regards,
Rashid

Answer 1

I study the source of log4j and find log4j can’t create new log file, it just print the error message to system.err when the log file was deleted

    /** 
     This method determines if there is a sense in attempting to append. 

     <p>It checks whether there is a set output target and also if 
     there is a set layout. If these checks fail, then the boolean 
     value <code>false</code> is returned. */  

  protected   boolean checkEntryConditions() {  
    if(this.closed) {  
      LogLog.warn("Not allowed to write to a closed appender.");  
      return false;  
    }  

    if(this.qw == null) {  
      errorHandler.error("No output stream or file set for the appender named ["+  
            name+"].");  
      return false;  
    }  

    if(this.layout == null) {  
      errorHandler.error("No layout set for the appender named ["+ name+"].");  
      return false;  
    }  
    return true;  
  }  

I think there are two workaround

1. create another cron thread to monitor the log file
2. add judge in getLog or getInstance (singleton), check the log file does exist, if not then init log4j