Setting up Log4j for Java Web Applications
Content of log4j.properties file would be as follows:
# Define the root logger with appender file
log = /usr/home/log4j
log4j.rootLogger = DEBUG, FILE
# Define the file appender
log4j.appender.FILE=org.apache.log4j.FileAppender
log4j.appender.FILE.File=${log}/log.out
# Define the layout for file appender
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%m%n
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Using log4j in Java Program:
The following Java class is a very simple example that initializes,
and then uses, the Log4J logging library for Java applications.
import org.apache.log4j.Logger; import java.io.*; import java.sql.SQLException; import java.util.*; public class log4jExample{ /* Get actual class name to be printed on */ static Logger log = Logger.getLogger(log4jExample .class); public static void main(String[] args) throws IOException,SQLException{ log.debug("Hello this is an debug message"); log.info("Hello this is an info message"); } }
Setting up Log4j for Java Web Applications
There are different ways to setup log4j for you web application.
log4j.logger.<appname>logger=DEBUG, C, fileappender |
Now use one of the methods below to add and enable Log4J in your web application
Method 1: Use Servlet to initialize log4j
Step 1: Put log4j.properties file in the right place
- Place 'log4j.properties' into the root of your classpath. See an example web application layout hereTip: when web application is deployed it should be in /WEB-INF/classes/log4j.properties.
- If using eclipse place 'log4j.properties' under your project_name/src directory
Step 2: Define the servlet mapping in web.xml
Add the following code to WEB-INF/web.xml
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| <servlet> <servlet-name>log4j-init</servlet-name> <servlet-class>com.FunkyWebapp.servlets.Log4jInit</servlet-class> <init-param> <param-name>log4j-init-file</param-name> <param-value>WEB-INF/classes/log4j.properties</param-value> </init-param> <load-on-startup>1</load-on-startup></servlet> |
Make sure to change the java class file path to be relevant to your project. 'com.FunkyWebapp.servlets.Log4jInit'
Step 3: Add the servlet you mapped in Step 2 to your application
Add the following servlet to your project
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| import javax.servlet.http.HttpServlet;import org.apache.log4j.PropertyConfigurator;public class Log4jInit extends HttpServlet { public void init() { String prefix = getServletContext().getRealPath("/"); String file = getInitParameter("log4j-init-file"); // if the log4j-init-file context parameter is not set, then no point in trying if(file != null){ PropertyConfigurator.configure(prefix+file); System.out.println("Log4J Logging started: " + prefix+file); } else{ System.out.println("Log4J Is not configured for your Application: " + prefix + file); } }} |
Make sure the <servlet-class> element in Step 2 matches the
fully qualified name of your servlet. And make sure it's in the right
package.
Step 4: Initialize the logger and start logging from other servlets in your web application
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| public class MyServlet extends HttpServlet {...private Logger log = Logger.getLogger("<appname>logger");...log.debug("Some string to print out");} |
Make sure the <appname> part matches with the line
log4j.logger.<appname>logger in the log4j.properties file
Notes:
When you initialize log4j in a servlet you will only be able to log from classes which are loaded after the servlet (eg. other servlets). You won't be able to do logging from a ServletContextListener for example.
When you initialize log4j in a servlet you will only be able to log from classes which are loaded after the servlet (eg. other servlets). You won't be able to do logging from a ServletContextListener for example.
Method 2: Initialize log4j in a ServletContextListener
Step 1: Put properties file in the right place
- Place 'log4j.properties' into the root of your classpath. See an example web application layout hereTip: when web application is deployed it should be in /WEB-INF/classes/log4j.properties.
- If using eclipse place 'log4j.properties' under your project_name/src directory
Step 2: Define a listener mapping in web.xml
Add the following servlet listener mapping in web.xml:
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| <listener> <listener-class> com.package.listeners.ApplicationServletContextListener </listener-class></listener> |
Step 3: Add the SerlvetContextListener class to the application
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| public class ApplicationServletContextListener implements ServletContextListener{ public void contextInitialized(ServletContextEvent event) { ServletContext ctx = e.getServletContext(); String prefix = ctx.getRealPath("/"); String file = "WEB-INF"+System.getProperty("file.separator")+"classes"+System.getProperty("file.separator")+"log4j.properties"; if(file != null) { PropertyConfigurator.configure(prefix+file); System.out.println("Log4J Logging started for application: " + prefix+file); } else { System.out.println("Log4J Is not configured for application Application: " + prefix+file); } } public void contextDestroyed(ServletContextEvent event) { }} |
Step 4: Define the logger and start logging from other servlets in your applications
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| public class MyServlet extends HttpServlet {...private Logger log = Logger.getLogger("<appname>logger");...log.debug("Some string to print out");} |
Notes:
- Easier to implement that Method 1
- All web application now has access to log4j (including listeners)
- Placing log4j initialization in a ServletContextListener allows initialization of log4j when your web application is loaded for the first time.
