Logging new, unsupported fields

[L Duperval]

Hi,

We want to use log4j to log even information for our application. We need to log information that isn't part of the log4j spec (for example, number of bytes transferred, userid for this event, etc.). Is there a documented way to do this or do I have to create my own logger?

My goal was to make an appender that received different types of objects as a parameter and the logger would know how that data would be logged to the database according to its type.

For example,

MyObject o1;
logger.info(o1);

OtherObject o2;
logger.info(o2);

would use the same table to log information. But in the cas of o1, it could (conceivably) log the userid, the hostname and some detailed information.

In the case of o2, it could log JRE version, Domain name, other info to the same table. That would probably be on top of some of the data that log4j logs.

has anyone ever done something like this?

Thanks,

L

[Paul Clapham]

If it's system-wide information you wanted to add (JRE version, host name etc.) then it's not the appender you need to play with. Here's the code I wrote for including host name in the logs; first a PatternParser that makes '%h' mean host name:

package me;
 
import java.net.InetAddress;
import java.net.UnknownHostException;
 
import org.apache.log4j.helpers.FormattingInfo;
import org.apache.log4j.helpers.PatternConverter;
import org.apache.log4j.spi.LoggingEvent;
 
public class MyPatternParser extends org.apache.log4j.helpers.PatternParser {
 
  /**
   * Constructor for MyPatternParser
   */
  public MyPatternParser(String arg0) {
    super(arg0);
  }
 
  public void finalizeConverter(char c) {
    PatternConverter pc = null;
    switch (c) {
    case 'h' :
      pc = new HostNamePatternConverter(formattingInfo);
      currentLiteral.setLength(0);
      addConverter(pc);
      break;
    default :
      super.finalizeConverter(c);
      break;
    }
  }
 
  private static class HostNamePatternConverter extends PatternConverter {
    HostNamePatternConverter(FormattingInfo formattingInfo) {
      super(formattingInfo);
    }
    public String convert(LoggingEvent event) {
      String literal = "unknown-host";
      try {
        literal = InetAddress.getLocalHost().getHostName();
      } catch(UnknownHostException uhe) {
      }
      return literal;
    }
 
  }
 
}

then a PatternLayout that uses that:

package me;
 
public class MyPatternLayout extends org.apache.log4j.PatternLayout {
 
  /**
   * Constructor for MyPatternLayout
   */
  public MyPatternLayout() {
    super();
  }
 
  protected org.apache.log4j.helpers.PatternParser createPatternParser(String pattern) {
    return new MyPatternParser(pattern);
  }
}

and finally a snippet from the log4j.properties file:

log4j.appender.standard.layout=me.MyPatternLayout
log4j.appender.standard.layout.ConversionPattern=%h %d{ISO8601} %-5p %c - %m%n