How to use log4j for EJB?

Log4j doesn't have a default initializing process? yes or no I am not sure right now.
Log4j call BasicConfigurator.configure(), for instance, to initialize the log4j.

For standard java application, we can implement this initialize process in main class.

For a web app, we can define a ServletContextListener implementation to do the initialization work when my web app is loaded. Is there anything similar for EJB?

The question how do this for EJBs?

Using External Configuration Files

Using External Configuration Files

Log4j is usually used in conjunction with external configuration files so that options do not have to be hard-coded within the software. The advantage of using an external configuration file is that changes can be made to the options without having to recompile the software. A disadvantage could be, that due to the io instructions used, it is slightly slower.

There are two ways in which one can specify the external configuration file: a plain text file or an XML file. Since everything is written in XML these days, this tutorial will focus on the XML approach but will also include relevant plain text examples. To begin with, examine the sample XML config file shown below:

The file starts with a standard XML declaration followed by a DOCTYPE declaration which indicates the DTD(Document Type Definition), this defines the structure of the XML file, what elements may be nested within other elements etc. This file is provided in the log4j distribution under src/java/org/apache/log4j/xml. Next comes the all-encapsulating log4j:configuration element, which was specified as the root element in the DOCTYPE declaration. Nested within the root element are two structures:

Here an Appender is created and called "ConsoleAppender", note that any name could have been chosen, it is because of the contrivity of examples that this name was chosen. The class for the appender is then specified in full, when referring to classes, one always uses the fully qualified class name. An Appender must always have a name and a class specified. Nested within Appender is the layout element which defines the layout to be a SimpleLayout. Layout must always have the class attribute.

The root element always exists and cannot be sub-classed. The example shows the priority being set to "debug" and the appender setup by including an appender-ref element, of which, more that one may be specified. See the file src/java/org/apache/log4j/xml/log4j.dtd in your log4j distribution for more information about the structure of an XML configuration file. The configuration file is pulled into the Java program like this:

DOMConfigurator.configure("configurationfile.xml");

The DOMConfigurator is used to initialise the log4j environment using a DOM tree. Here is the example xml configuration file: plainlog4jconfig.xml. Here is a program which implements this configuration file: files/externalxmltest.java:

import org.apache.log4j.Logger; import org.apache.log4j.xml.DOMConfigurator; public class externalxmltest { static Logger logger = Logger.getLogger(externalxmltest.class); public static void main(String args[]) { DOMConfigurator.configure("xmllog4jconfig.xml"); logger.debug("Here is some DEBUG"); logger.info("Here is some INFO"); logger.warn("Here is some WARN"); logger.error("Here is some ERROR"); logger.fatal("Here is some FATAL"); } }

Here is an XML configuration file for a Logger implementing a FileAppender using a PatternLayout:

You can download this example from here: xmllog4jconfig2.xml. For more examples of using xml files to configure a log4j environment, see the src/java/org/apache/log4j/xml/examples/ directory in the log4j distribution.

Here is the configuration file discussed above, expressed in the form of a plain text file:

# initialise root logger with level DEBUG and call it BLAH log4j.rootLogger=DEBUG, BLAH # add a ConsoleAppender to the logger BLAH log4j.appender.BLAH=org.apache.log4j.ConsoleAppender # set set that layout to be SimpleLayout log4j.appender.BLAH.layout=org.apache.log4j.SimpleLayout

You can download it here: plainlog4jconfig.txt. Here is a program implementing this:

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;
public class externalplaintest {
  static Logger logger = Logger.getLogger(externalplaintest.class);
  public static void main(String args[]) {
     PropertyConfigurator.configure("plainlog4jconfig.xml");
     logger.debug("Here is some DEBUG");
     logger.info("Here is some INFO");
     logger.warn("Here is some WARN");
     logger.error("Here is some ERROR");
     logger.fatal("Here is some FATAL");
  }
}

log4j configuration file

An example for log4j configuration file