Recipe13.3.Adding Logging to Your Own Classes

Recipe 13.3. Adding Logging to Your Own Classes

Problem

You want to log messages of varying severity from your own classes.

Solution

Use Commons Logging within your own classes, as shown in Example 13-3.

Example 13-3. Using Commons Logging in a custom class

package com.fooware.barapp; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; public class MyClazz {     private static Log log = LogFactory.getLog(MyClazz.class);     public void doSomething( ) {         log.debug("About to do something.");         try {             //call something that throws an exception         } catch (Exception e) {             log.error("An exception occured doing something.", e);         }         log.info("Successfully did something.");     } }

Discussion

Any critical application should use logging of some kind. Relying on System.out.println( ) limits logging flexibility and can significantly downgrade application performance. You can roll your own logging mechanism, as many shops have done, or you can take advantage of frameworks and APIs such as Log4J and Commons Logging that make logging easy.

The Solution uses the Commons Logging API. Messages are logged to a logging category. If you use the class name as the category, you can control logging at the class level. In addition, you can use the package name as a hierarchy. The Commons Logging API supports the following logging levels in increasing order of severity:

Trace
Debug
Info
Warn
Error
Fatal

Using Commons Logging gives you the flexibility of choosing a logging implementation as desired. If you were using Log4J, you would configure logging for your package or classes as was done for the Struts packages in Recipe 13.2. Example 13-4 shows the log4j.properties file that enables console logging of errors and warnings for the class in the Solution.

Example 13-4. Log4J configuration for a custom class

log4j.rootLogger=ERROR,Console log4j.logger.com.foo.bar.MyClazz=WARN,Console # # The output information consists of relative time, log level, thread # name, logger name, nested diagnostic context and the message in that # order. log4j.appender.Console=org.apache.log4j.ConsoleAppender log4j.appender.Console.layout=org.apache.log4j.PatternLayout log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p %c - %m%n

Recipe13.3.Adding Logging to Your Own Classes