Colourify the level of a log4j message by overriding the PatternLayout

ColourPatternLayout.java

import java.util.HashMap;
import java.util.Map;

import org.apache.log4j.Level;
import org.apache.log4j.PatternLayout;
import org.apache.log4j.helpers.PatternConverter;
import org.apache.log4j.helpers.PatternParser;
import org.apache.log4j.spi.LoggingEvent;

public class ColourPatternLayout extends PatternLayout {
    private static boolean coloursEnabled = "true".equalsIgnoreCase(System.getenv("LOG_COLOURS"));

    private static Map<Level, String> lookup = new HashMap<Level, String>();
    static {
    	lookup.put(Level.TRACE, "\u001b[0;43mTRACE\u001b[m");
    	lookup.put(Level.DEBUG, "\u001b[0;90mDEBUG\u001b[m");
    	lookup.put(Level.INFO,  "\u001b[0;36mINFO \u001b[m");
    	lookup.put(Level.WARN,  "\u001b[0;33mWARN \u001b[m");
    	lookup.put(Level.ERROR, "\u001b[0;31mERROR\u001b[m");
    	lookup.put(Level.FATAL, "\u001b[1;31mFATAL\u001b[m");
    }
    
    
    @Override protected PatternParser createPatternParser(String pattern) {
        return new PatternParser(pattern) {
    	    @Override protected void finalizeConverter(char c) {
    	        if (coloursEnabled && c == 'p') {
    		    addConverter(new PatternConverter() {
                        protected String convert(LoggingEvent event) {
    			    return lookup.get(event.getLevel());
    			}
    		    });
    		} else {
    		    super.finalizeConverter(c);
    		}
    	    }
    	};
    };
}