programming panda

Default location of log4j properties is in /WEB-INF/classes/logj4.properties. There are ways to point log4j to different properties. In spring, we can do something like this.

<!-- log4j setting -->
    <bean id="log4jInitialization"
 class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
  <property name="targetClass"
   value="org.springframework.util.Log4jConfigurer" />
  <property name="targetMethod" value="initLogging" />
  <property name="arguments">
   <list>
    <value>log4j.properties</value>
   </list>
  </property>
 </bean>

where initLogging takes (String location), you can use absolute path or relative path here. But a more elegant way is to use a variable for the application root. like this

<value>${webapp.root}/${log4j.properties.location}</value>

You can get the ${webapp.root} from webAppRootKey. To bring it to the next level we can group all configs into 1 properties file and that will make the build process easier.

The full setup looks something like this

/WEB-INF/web.xml

<listener>
        <listener-class>org.springframework.web.util.WebAppRootListener</listener-class>
    </listener>
<listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/applicationContext.xml
</param-value>
    </context-param>
    <context-param>
        <param-name>webAppRootKey</param-name>
        <param-value>webapp.root</param-value>
    </context-param>

/WEB-INF/applicationContext.xml

<bean id="propertyConfigurer"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
      <property name="locations">
      <list>
                <value>/WEB-INF/spring-config/dev.properties</value>
   </list>
   </property>
 </bean>
<!-- log4j setting -->
    <bean id="log4jInitialization"
 class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
  <property name="targetClass"
   value="org.springframework.util.Log4jConfigurer"/>
  <property name="targetMethod" value="initLogging"/>
  <property name="arguments">
   <list>
    <value>${webapp.root}/${log4j.properties.location}</value>
   </list>
  </property>
 </bean>

/WEB-INF/spring-config/dev.properties

#log4j setting
log4j.properties.location=WEB-INF/log4j-config/log4j.dev.properties

/WEB-INF/log4j-config/log4j.dev.properties

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.Threshold=DEBUG
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

log4j.rootLogger=DEBUG, stdout

/WEB-INF/log4j-config/log4j.prod.properties

# Configuration for receiving e-mails when ERROR messages occur.
log4j.appender.mail=org.apache.log4j.net.SMTPAppender
log4j.appender.mail.To=to@mydomain.com
log4j.appender.mail.From=from@mydomain.com
log4j.appender.mail.SMTPHost=smtp.mydomain.com
log4j.appender.mail.Threshold=ERROR
log4j.appender.mail.BufferSize=1
log4j.appender.mail.Subject=An application error occured
log4j.appender.mail.layout=org.apache.log4j.HTMLLayout

# Standrd System.out appender
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.Threshold=INFO
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

log4j.rootLogger=INFO, stdout, mail

Apache log4j is an excellent logging facility to log application information. It is extremely easy to setup and it is very powerful. It comes with an email appender by default which you can config it to sends email when you log.

Example: Logs message to standard system.out on INFO and Sends email when an application error occurs

# Configuration for receiving e-mails when ERROR messages occur.
log4j.appender.mail=org.apache.log4j.net.SMTPAppender
log4j.appender.mail.To=to@mydomain.com
log4j.appender.mail.From=from@mydomain.com
log4j.appender.mail.SMTPHost=smtp.mydomain.com
log4j.appender.mail.Threshold=ERROR
log4j.appender.mail.BufferSize=1
log4j.appender.mail.Subject=An application error occured
log4j.appender.mail.layout=org.apache.log4j.HTMLLayout

# Standrd System.out appender
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.Threshold=INFO
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

log4j.rootLogger=INFO, stdout, mail

This is pretty simple. The only setting that controls what to send is the Threshold property of the appender.