GWT 2.1: logging API

One of the new functionality implemented into GWT 2.1 M2 is a Java logging API. The development team doesn't choose to implements a new API, but to use the logging API provided by Java SDK by emulating it. So, to use it, you just should create a logger as usual in your class and use it like that:

public class Gwt_log implements EntryPoint {
// create the logger
private static final Logger logger = Logger.getLogger(Gwt_log.class.getName());

public void onModuleLoad() {
// use it
logger.info("Module is loading");
}
}

As usual in GWT, your module, to use this API, must inherit from the logging module:

<inherits name='com.google.gwt.logging.Logging'/>

Inherit from this module set a numerous properties dedicated to logging API:

• gwt.logging.enabled: enable or disable logging API, set to TRUE by default,
• gwt.logging.logLevel: logging level, by default, set to INFO. Other available values are: ALL, FINEST, FINER, FINE, CONFIG, INFO, WARNING, SEVERE,
• gwt.logging.consoleHandler: log message into the IDE console, by default, set to ENABLED. It doesn't have any effect in production mode,
• gwt.logging.developmentModeHandler: log message into dev mode console. By default, set to ENABLED,
• gwt.logging.firebugHandler: log message into Fiebug console. By default, set to ENABLED,
• gwt.logging.popupHandler: log message into a popup window into the GWT application. By default, set to ENABLED,
• gwt.logging.systemHandler: log message with a level upper than WARNING on System.err, else, on System.out. By default, set to ENABLED,
• gwt.logging.simpleRemoteHandler: log message on server side by using a service defined by GWT. By default, set to ENABLED.

To use the remote logging capabilities of GWT, an additional effort is needed. GWT provides a service that logs message on server side. It implements a simple delegate log, by using the standard Java logging API, of the messages logged on client side. So, the logging on server side can be configured in any manner you usually do. You only need to declare the service into the file web.xml as following:

<servlet>
<servlet-name>remoteLogger</servlet-name>
<servlet-class>com.google.gwt.logging.server.RemoteLoggingServiceImpl</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>remoteLogger</servlet-name>
<url-pattern>/gwt_log/remote_logging</url-pattern>
</servlet-mapping>

In future post, I will explain how to use the MVP framework, the validation API, the new paging table widgets, and the new binding mechanism between client and server.

For other feature, have a look to: GWT 2.1: validation API.