java.lang.Object
   org.springframework.web.util.Log4jWebConfigurer

WARNING: Assumes an expanded WAR file, both for loading the configuration file and for writing the log files. If you want to keep your WAR unexpanded or don't need application-specific log files within the WAR directory, don't use log4j setup within the application (thus, don't use Log4jConfigListener or Log4jConfigServlet). Instead, use a global, VM-wide log4j setup (for example, in JBoss) or JDK 1.4's java.util.logging (which is global too).

Supports three init parameters at the servlet context level (that is, context-param entries in web.xml):

• "log4jConfigLocation":
  Location of the log4j config file; either a "classpath:" location (e.g. "classpath:myLog4j.properties"), an absolute file URL (e.g. "file:C:/log4j.properties), or a plain path relative to the web application root directory (e.g. "/WEB-INF/log4j.properties"). If not specified, default log4j initialization will apply ("log4j.properties" or "log4j.xml" in the class path; see the log4j documentation for details).
• "log4jRefreshInterval":
  Interval between config file refresh checks, in milliseconds. If not specified, no refresh checks will happen, which avoids starting log4j's watchdog thread.
• "log4jExposeWebAppRoot":
  Whether the web app root system property should be exposed, allowing for log file paths relative to the web application root directory. Default is "true"; specify "false" to suppress expose of the web app root system property. See below for details on how to use this system property in log file locations.

Note: initLogging should be called before any other Spring activity (when using log4j), for proper initialization before any Spring logging attempts.

Log4j's watchdog thread will asynchronously check whether the timestamp of the config file has changed, using the given interval between checks. A refresh interval of 1000 milliseconds (one second), which allows to do on-demand log level changes with immediate effect, is not unfeasible.

WARNING: Log4j's watchdog thread does not terminate until VM shutdown; in particular, it does not terminate on LogManager shutdown. Therefore, it is recommended to not use config file refreshing in a production J2EE environment; the watchdog thread would not stop on application shutdown there.

By default, this configurer automatically sets the web app root system property, for "${key}" substitutions within log file locations in the log4j config file, allowing for log file paths relative to the web application root directory. The default system property key is "webapp.root", to be used in a log4j config file like as follows:

log4j.appender.myfile.File=${webapp.root}/WEB-INF/demo.log

Alternatively, specify a unique context-param "webAppRootKey" per web application. For example, with "webAppRootKey = "demo.root":

log4j.appender.myfile.File=${demo.root}/WEB-INF/demo.log

WARNING: Some containers (like Tomcat) do not keep system properties separate per web app. You have to use unique "webAppRootKey" context-params per web app then, to avoid clashes. Other containers like Resin do isolate each web app's system properties: Here you can use the default key (i.e. no "webAppRootKey" context-param at all) without worrying.

Also see:

org.springframework.util.Log4jConfigurer
Log4jConfigListener
Log4jConfigServlet
author: Juergen - Hoeller

since: 12.08.2003 -

 public static  void initLogging(ServletContext servletContext) 
{
	                 	 
		// Expose the web app root system property.
		if (exposeWebAppRoot(servletContext)) {
			WebUtils.setWebAppRootSystemProperty(servletContext);
		}
		// Only perform custom log4j initialization in case of a config file.
		String location = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
		if (location != null) {
			// Perform actual log4j initialization; else rely on log4j's default initialization.
			try {
				// Return a URL (e.g. "classpath:" or "file:") as-is;
				// consider a plain file path as relative to the web application root directory.
				if (!ResourceUtils.isUrl(location)) {
					// Resolve system property placeholders before resolving real path.
					location = SystemPropertyUtils.resolvePlaceholders(location);
					location = WebUtils.getRealPath(servletContext, location);
				}
				// Write log message to server log.
				servletContext.log("Initializing log4j from [" + location + "]");
				// Check whether refresh interval was specified.
				String intervalString = servletContext.getInitParameter(REFRESH_INTERVAL_PARAM);
				if (intervalString != null) {
					// Initialize with refresh interval, i.e. with log4j's watchdog thread,
					// checking the file in the background.
					try {
						long refreshInterval = Long.parseLong(intervalString);
						Log4jConfigurer.initLogging(location, refreshInterval);
					}
					catch (NumberFormatException ex) {
						throw new IllegalArgumentException("Invalid 'log4jRefreshInterval' parameter: " + ex.getMessage());
					}
				}
				else {
					// Initialize without refresh check, i.e. without log4j's watchdog thread.
					Log4jConfigurer.initLogging(location);
				}
			}
			catch (FileNotFoundException ex) {
				throw new IllegalArgumentException("Invalid 'log4jConfigLocation' parameter: " + ex.getMessage());
			}
		}
}

 public static  void shutdownLogging(ServletContext servletContext) 
{
		servletContext.log("Shutting down log4j");
		try {
			Log4jConfigurer.shutdownLogging();
		}
		finally {
			// Remove the web app root system property.
			if (exposeWebAppRoot(servletContext)) {
				WebUtils.removeWebAppRootSystemProperty(servletContext);
			}
		}
}