Yesterday I decided to use a custom formatter for my logfiles. Why? Because I thought it would be nice to have a nicely formatted piece of logfile rather than the old-school, black & white log files we all know:
But wait – there is more than just look & feel, writing your own formatter lets you control how exceptions are beeing logged and you can create Hyperlinks to lookup a solution for a problem directly from the logfile!
And here is what you need:
1. The Formatter
</pre>
package helper;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.logging.Formatter;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.LogRecord;
/**
* @see CustomHtmlFormatter
* @author christian.meyer
* @author stockholmconsulting
* @version 1.0, November 2010
*/
public class CustomHtmlFormatter extends Formatter
{
// This method is called for every log records
public String format(LogRecord rec)
{
StringBuffer buf = new StringBuffer(1000);
buf.append("<tr>");
//Here we use an alternate background color for every 2nd row
//(just to improve readability)
/*if(row%2==0)
buf.append("<tr>");
else
buf.append("<tr bgcolor = #C0C0C0>");*/
buf.append("<td>");
buf.append(getFormattedDate(rec.getMillis()));
buf.append("</td>");
buf.append("<td>");
buf.append(rec.getLoggerName());
buf.append("</td>");
buf.append("<td>");
// Set the font color for levels >= WARNING to red
if (rec.getLevel().intValue() >= Level.WARNING.intValue()){
buf.append("<font color=\"#FF0000\">");
}
buf.append(rec.getLevel());
buf.append("</td>");
buf.append("<td>");
buf.append(formatMessage(rec));
//This happens if we get a throwable: we're iterating through the
//stacktrace & printing everything nicely formatted
if(rec.getThrown()!=null){
buf.append("<font color=\"#FF0000\">");
buf.append(": " + "<a href=\"http://www.google.de/search?q=" + rec.getThrown() +
"\" title= \"Search at Google\" target=\"_blank\">" + rec.getThrown() + "</a><br>");
StackTraceElement[] stackTrace = rec.getThrown().getStackTrace();
for (StackTraceElement element : stackTrace)
{
String exceptionMsg = "at " + element.getClassName() +
" (" + element.getMethodName() + ":" +
element.getLineNumber() + ")<br>";
buf.append(exceptionMsg);
}
}
buf.append('\n');
buf.append("/td>");
buf.append("</tr>\n");
return buf.toString();
}
private String getFormattedDate(long millisecs)
{
SimpleDateFormat date_format = new SimpleDateFormat("HH:mm:ss");
Date resultdate = new Date(millisecs);
return date_format.format(resultdate);
}
// This method creates the basic HTML structure. You can add your own
// CSS after the <style type="text/css"> tag
public String getHead(Handler h)
{
return "<HTML>\n<HEAD><title>Datamasker logfile</title>\n" +
"<link rel=\"stylesheet\" type=\"text/css\" href=\"datamasker.css\" />" +
/*"<style type=\"text/css\">\n" +
"caption {font-size: 1.7em; color: #F06; text-align: left;}\n" +
"heading {font-family: Arial; font-size: medium; color: #555; text-decoration:underline; font-weight: bold; text-align: center }\n" +
"footer {font-family: Arial; font-size: x-small; color: #555; text-align: right }\n" +
"body {font-family: Arial; font-size: small; color: black; text-align: left }\n" +
"table {margin: 0; padding: 0; border-collapse: collapse; width: 100%;}\n" +
"td, th {padding: 1px 4px; border-bottom: 1px solid #EEE;}\n" +
"td + td {border-left: 1px solid #FAFAFA; color: #999;}\n" +
"td + td + td {color: #666; border-left: none;}\n" +
"td a {color: #444; text-decoration: none; text-align: left;}\n" +
"td a, th a {display: block; width: 100%;}\n" +
"td a:hover {background: #444; color: #FFF;}\n" +
"tfoot th {text-align: left;}\n" +
"th {text-align: left;}\n" +
"th + th {text-align: left;}\n" +
"th + th + th {text-align: left;}\n" +
"th a {color: #F06; text-decoration: none; font-size: 1.1em;}\n" +
"th a:visited {color: #F69;}\n" +
"th a:hover {color: #F06; text-decoration: underline;}\n" +
"thead tr, tfoot tr {color: #555; font-size: 0.8em;}\n" +
"tr {font: 12px sans-serif; background: repeat-x #F8F8F8; color: #666;}\n" +
"tr:hover {background: #FFF;}\n" +
"</style>\n" +*/
"</HEAD>\n" +
"<BODY>\n" +
"<heading>Datamasker Logfile: " + (new Date()) +"</heading><br>\n<br>" +
"\n<PRE>\n" +
"<table rules=\"all\"; cellpadding=\"2px\">\n " +
"<tr bgcolor = #A9A9A9><th>Time</th><th>Source</th><th>Type</th><th>Message</th></tr>\n";
}
// This method appends the necessary closing tags
public String getTail(Handler h)
{
return "</table>\n</PRE>\n <footer>Copyright Stockholmconsulting 2010</footer> \n </BODY>\n</HTML>\n";
}
}
<pre>
2. A logger which writes to a file using our formatter
private static final Logger rootLogger = Logger.getLogger(MainClass.class.getName());
rootLogger.setLevel(Level.INFO);
fileHTML = new FileHandler("Logging.html");
//Create HTML Formatter
formatterHTML = new CustomHtmlFormatter();
fileHTML.setFormatter(formatterHTML);
rootLogger.addHandler(fileHTML);
rootLogger .info("Starting logfile");
rootLogger.entering(this.getClass().getName(), "theNameOfTheMethod");
rootLogger .severe("Serious information");
Throwable ex = new IllegalArgumentException("Some exception text");
rootLogger .log(Level.SEVERE, "Some message", ex);
rootLogger.exiting(this.getClass().toString(), "End of method");
Of course you can put the css into a file, there is no need to put everything into the code.
In this case, simply put the following line right after the <Head>:
“<link rel=\”stylesheet\” type=\”text/css\” href=\”nameOfYourCSSFile.css\” />”
As you can see it is pretty simple to create your own formatter, of course it is possible to use your own CSS, Logo, whatever you want – I hope you enjoy it 
