Logging in Spring

Logging is important for an application. It gives insider information :-) It helps us understand what is happening inside the engine by recording parameters silently and provides vital information. It helps in providing system related information like health status, debugging and provides critical support during production trouble shooting and unexplained failure.

We need unified logging system within our application. We integrate multiple different components/packages to our application. We always do that in real time scenario, for example we integrate Quartz package for scheduling. Then imagine, each such external system requires its own separate logging configuration and each will do their own logging. That will be horrible man! Its like having four steering in a car.

Spring provides central control in terms of logging. We can have one central logging configuration file and control all logging output via that. There are many external components integrated with Spring.

Jakarta Commons Logging API (JCL) is the only mandatory external dependency for Spring!

spring-core defines a dependency on commons-logging. JCL is a thin logging framework that serves as an abstraction for other logging APIs. JCL interface looks similar to Log4j. So, as a Spring developer what should we do? We need to make sure the dependency on JCL is met. commons-logging is an implementation for JCL and it can be used to solve the dependency.

We should add commons-logging to the Spring application. commons-logging discovers what are the logging framework added in the application and chooses one that suits the best and uses it for logging, if we have not added any logging API, then it uses java.util.Logging framework. We can also configure commons-logging to use a certain logging framework.

Switch-off commons-logging

We say highly configurable and we say that there is a hard dependency with JCL. Yes it is but we have our choice of implementation. JCL is fine but I don’t like the implementation commons-logging. Ok, how do we force Spring not to use commons-logging? Yes it is possible lets disable commons-logging and use some other alternate implementation of JCL. It can be achieved easily when we use Maven,

<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>3.0.0.RELEASE</version>
<scope>runtime</scope>
<exclusions>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>

add the above to the dependencies in maven pom file. We are excluding commons-logging from spring core.

Alternate for JCL – SLF4J

Spring says,

“SLF4J is a cleaner dependency and more efficient at runtime than commons-logging because it uses compile-time bindings instead of runtime discovery of the other logging frameworks it integrates…”

no I didn’t say that, don’t shout at me! I am afraid ;-))

<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>3.0.0.RELEASE</version>
<scope>runtime</scope>
<exclusions>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.5.8</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.5.8</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.5.8</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.14</version>
<scope>runtime</scope>
</dependency>
</dependencies>

Use Log4J with Spring

Now lets leave JCL and look at underlying logging framework. We want to use Log4j as the underlying logging component how do we do it. Assume we are using commons-logging then it is simple and direct, just add the log4j libraries at classpath. We can do this by adding a dependency in maven pom.

<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>3.0.0.RELEASE</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.14</version>
<scope>runtime</scope>
</dependency>
</dependencies>

Sample log4j.properties to use,

log4j.rootCategory=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c{2}:%L - %m%n
log4j.category.org.springframework.beans.factory=DEBUG

Note:
We have a common problem related to Spring logging configuration. When we use use Tomcat kind of servlet containers it is ok. When we use muscular IBM Websphere Application Server (WAS) kind of servers, they come bundled with their own implementation of JCL. It conflicts with Spring configuration. Just disable commons-logging and things will become good.