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# Logging

## Logging support

> As from Struts 2.5 version, the logging layer is deprecated and Struts uses Log4j2 The logging layer will be dropped with the next major release.

XWork provides its own layer to support logging - it allows to use many different implementations.

Currently XWork provides support for the following libraries (in that order base on classpath discovery):

- Commons Logging
- SLF4J
- Log4j2
- JDK Logger

## Usage

To use given type of library add it as a Maven dependency or drop into WEB-INF/lib folder. XWork LoggerFactory class will use given logging provider if available.

To add logging to your application simply declare a Logger as follow:

    import com.opensymphony.xwork2.util.logging.Logger;
    import com.opensymphony.xwork2.util.logging.LoggerFactory;

    public class MyAction {

        private static final Logger LOG = LoggerFactory.getLogger(MyAction.class);

        private String userName;

        public String execute() {
            LOG.debug("MyAction executed with UserName [#0]", userName);
            return "success";
        }

        // getter / setter

    }

## Implementing my own factory

You plug in your own logging solution, simple extend LoggerFactory class and provide a delegate which implements Logger interface, like below:

JdkLoggerFactory which adds support for JDK logging

    import com.opensymphony.xwork2.util.logging.Logger;
    import com.opensymphony.xwork2.util.logging.LoggerFactory;

    /**
     * Creates jdk loggers
     */
    public class JdkLoggerFactory extends LoggerFactory {

        @Override
        protected Logger getLoggerImpl(Class<?> cls) {
            return new JdkLogger(java.util.logging.Logger.getLogger(cls.getName()));
        }

        @Override
        protected Logger getLoggerImpl(String name) {
            return new JdkLogger(java.util.logging.Logger.getLogger(name));
        }
    }

JdkLogger is a wrapper around java.util.logging.Logger and implements Logger interface

    import com.opensymphony.xwork2.util.logging.Logger;
    import com.opensymphony.xwork2.util.logging.LoggerUtils;

    import java.util.logging.Level;

    /**
     * Delegates to jdk logger.  Maps fatal to Level.SEVERE along with error.
     */
    public class JdkLogger implements Logger {

        private java.util.logging.Logger log;

        public JdkLogger(java.util.logging.Logger log) {
            this.log = log;
        }

        public void error(String msg, String... args) {
            log.log(Level.SEVERE, LoggerUtils.format(msg, args));
        }

        public void error(String msg, Throwable ex, String... args) {
            log.log(Level.SEVERE, LoggerUtils.format(msg, args), ex);
        }

        ...
    }

Check the source code to see more details.

## Defining which factory to use

Now you must tell XWork/Struts2 to use your implementation, just define system property like below:

    -Dxwork.loggerFactory=com.demo.MyLoggerFactory

you can use the same to explicit tell the framework which implementation to use and don’t depend on class discovery, eg.:

    -Dxwork.loggerFactory=com.opensymphony.xwork2.util.logging.slf4j.Slf4jLoggerFactory

or

    -Dxwork.loggerFactory=com.opensymphony.xwork2.util.logging.log4j2.Log4j2LoggerFactory

will enable Slf4j or Log4j2 even if there is commons-logging on classpath available (commons-logging is the first LoggerFactory to look for).