- Why Logging?
- Start Logging
- Changing the Log Level
- Logger Demystified
- Adding the FileHandler
- Adding a Custom Formatter
- Adding a Filter
- Conclusion
Like this article? We recommend
Like this article? We recommend
Like this article? We recommend
Adding a Custom Formatter
In this exercise, we'll add a custom HTML Formatter for our LogRecords. The Formatter class is shown below:
public class Formatter {
public abstract String
format(String s);
public String
formatMessage(String s);
public String getHead(Handler h);
public String getTail(Handler h);
}
To develop our own custom Formatter, we'll override the format method, using methods to access specific data from the LogRecord. The getHead() and getTail() methods are used for well-formed output formats such as XML. The following code describes a formatter class used to generate very simple HTML output:
import java.util.logging.*;
import java.util.Date;
// This custom formatter formats the logs into HTML format
// Each record is logged to a single line
class MyCustomFormatter extends Formatter {
// This method is called for every log record
public String format(LogRecord rec) {
StringBuffer sb = new StringBuffer(1000);
// give a red color to any messages with levels >= WARNING
if (rec.getLevel().intValue() >= Level.WARNING.intValue()) {
sb.append("<font color=\"red\">");
sb.append(rec.getLevel());
sb.append("</font>");
} else {
sb.append(rec.getLevel());
}
sb.append(' ');
sb.append(formatMessage(rec));
sb.append('\n');
return sb.toString();
}
// This method is called when the handler is created
public String getHead(Handler h) {
return "<HTML><HEAD> My Custom Log from "+(new Date())+"</HEAD><BODY><H1>The logs</H1><PRE>\n";
}
// This method is called when the handler is closed
public String getTail(Handler h) {
return "</PRE></BODY></HTML>\n";
}
}
In this example, we'll modify the SimpleLogging.java file that we developed to replace the mylogging.properties file, to demonstrate that you always have the option to make calls to these classes programmatically.
package com.informit;
import java.io.*;
import java.util.logging.*;
public class SimpleLogging {
public static void main(String[] args) {
// Get a logger
Logger logger = Logger.getLogger("com.informit.SimpleLogging");
try {
// Create a file handler that uses the custom formatter
FileHandler fh = new FileHandler("mycustom.html");
fh.setFormatter(new MyCustomFormatter());
logger.addHandler(fh);
} catch (IOException e) {
}
// Log a few messages at different severity levels
// There are seven different levels for logging
// You can choose a method specific to the logging level or
// the generic log method as shown
logger.severe("Something really bad happened ");
logger.warning("This is a warning");
logger.log(Level.WARNING,"This is also a warning");
logger.info("Just for your info");
logger.config("A configuration message");
logger.fine("A fine message");
logger.finer("A finer message");
logger.finest("A finest message");
logger.log(Level.FINEST,"This is also a finest message");
}
}
On execution, the program produces the file mycustom.html (see Figure 1).
)
Figure 1 The HTML output using the custom Formatter.
In this way you can extend the Formatter to output the log records in the format that you find to be most desirable.