public int decide(LoggingEvent event) 
{
    String msg = event.getRenderedMessage();
    if(msg == null ||  stringToMatch == null)
      return Filter.NEUTRAL;
    if( msg.indexOf(stringToMatch) == -1 ) {
      return Filter.NEUTRAL;
    } else { // we've got a match
      if(acceptOnMatch) {
	return Filter.ACCEPT;
      } else {
	return Filter.DENY;
      }
    }
}

Returns Filter#NEUTRAL is there is no string match.

 public boolean getAcceptOnMatch() 
{
    return acceptOnMatch;
}

 public String[] getOptionStrings() 
{
  
    return new String[] {STRING_TO_MATCH_OPTION, ACCEPT_ON_MATCH_OPTION};
}

 public String getStringToMatch() 
{
    return stringToMatch;
}

 public  void setAcceptOnMatch(boolean acceptOnMatch) 
{
    this.acceptOnMatch = acceptOnMatch;
}

 public  void setOption(String key,
    String value) 
{
 
    if(key.equalsIgnoreCase(STRING_TO_MATCH_OPTION)) {
      stringToMatch = value;
    } else if (key.equalsIgnoreCase(ACCEPT_ON_MATCH_OPTION)) {
      acceptOnMatch = OptionConverter.toBoolean(value, acceptOnMatch);
    }
}

 public  void setStringToMatch(String s) 
{
    stringToMatch = s;
}