How to Create a Custom Appender in log4j2?

In log4j2, you would create a plugin for create custom appender in log4j2.

When you annotate your custom Appender class with @Plugin(name=”MyCustomAppender”, category=”core” elementType=”appender” ,printObject=true) the plugin name becomes the configuration element name, so a configuration with your custom appender would then look like this:

Log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>

<Configuration status="warn" packages="com.madhu.appender">

    <Appenders>

        <MyCustomAppender name="myapp" >

       <PatternLayout pattern="serial no: %sn |  Date: %d |  level:%level | class name:%logger | method name:%M() |  line number:%L |  Location: %l | message:%m%n" />

        </MyCustomAppender>

    </Appenders>

       <Loggers>

              <Root level="all" additivity="false">

                     <AppenderRef ref="myapp" />

              </Root>

       </Loggers>

</Configuration>

In log4j2.xml file don’t forgot packages attribute here configure your custom appender package.

Now we are create plugin for appender.

MyCustomImpl.java

@Plugin(name="MyCustomAppender", category="Core", elementType="appender", printObject=true)

public class MyCustomImpl extends AbstractAppender {

    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();

    private final Lock readLock = rwLock.readLock();

    protected MyCustomImpl(String name, Filter filter,

            Layout<? extends Serializable> layout, final boolean ignoreExceptions) {

        super(name, filter, layout, ignoreExceptions);

    }

    @PluginFactory

    public static MyCustomImpl createAppender(

            @PluginAttribute("name") String name,

            @PluginElement("Layout") Layout<? extends Serializable> layout,

            @PluginElement("Filter") final Filter filter,

            @PluginAttribute("otherAttribute") String otherAttribute) {

        if (name == null) {

            LOGGER.error("No name provided for MyCustomAppenderImp");

            return null;

        }

        if (layout == null) {

            layout = PatternLayout.createDefaultLayout();

        }

        return new MyCustomImpl(name, filter, layout, true);

}

       @Override

       public void append(LogEvent event) {

                readLock.lock();

               try {    

                   final byte[] bytes = getLayout().toByteArray(event);

// here I am printing logs into console

                   System.out.println("LOG: " +new String(bytes, "UTF-8"));

               } catch (Exception ex) {

                   if (!ignoreExceptions()) {

                       throw new AppenderLoggingException(ex);

                   }

               } finally {

                   readLock.unlock();

               }

       }

}

Now we can test our custom appender. For this we can write one test class.

Note: Here custom appender plugin name and configuration appender name is same otherwise its won’t work.

Test.java

public class Test {

       public static final Logger LOGGER=LogManager.getLogger(Test.class);

public static void main(String[] args) throws IOException {

       LOGGER.info("this is info message");

       LOGGER.warn("this is warning message");

      

}

}

The output comes like below.

LOG: serial no: 1 |  Date: 2015-06-23 15:32:56,069 |  level:INFO | class name:com.madhu.appender.Test | method name:main() |  line number:15 |  Location: com.madhu.appender.Test.main(Test.java:15) | message:this is info message

LOG: serial no: 2 |  Date: 2015-06-23 15:32:56,072 |  level:WARN | class name:com.madhu.appender.Test | method name:main() |  line number:16 |  Location: com.madhu.appender.Test.main(Test.java:16) | message:this is warning message