Spring Boot中触发log4j2的logger.error()时触发自定义方法

Question

I am using Spring Boot with log4j2 - and I'd like to trigger a custom method in a '@Service' class when logger.error(...) is triggered.

For example,

@Service
public class Foo {
    private final Logger logger = LogManager.getLogger(getClass());
    ...
    public void doSomething() {
        try {
            ...
        }
        catch (Exception e) {
            logger.error("Error!", e); // When `error` is triggered...
        }
    }
}

// Other class
@Service
public class Bar {
    @Autowired private NotificationService notificationService;

    public void triggeredOnError() { // I'd like to trigger this method
        this.notificationService.notifySomething();
    }
}

I'd like to know this is possible in log4j2 with Spring Boot. The thing is, I just want to trigger the default method logger.error(...) since I don't want to change the default behavior of log4j2 . I researched a bit - and filter or adapter might be the solution here, but I am not really sure how to achieve this. Please help me out!

Answer 1

While an appender would work as Mark suggests, I would implement a Filter. A Filter can be placed in four different locations in Log4j 2 and has the option of forcing the log event to be logged, forcing it to not be logged or just continue on with the normal evaluation of whether it should be logged. But a filter can always be configured with onMatch=NEUTRAL and onMismatch=NEUTRAL so that it really has no effect on whether the log event is processed but allows some other processing to take place. In addition, Filters are much easier to write than an Appender.

You can find a sample Filter at http://logging.apache.org/log4j/2.x/manual/extending.html#Filters

What you should not do in a Filter though, is use it as a way to write the log event to some destination. That is exactly what Appenders are for.

Answer 2

IMO the easiest way to achieve that is to create a special appender and in Log4j2 configuration associate it with a logger of your choice (or maybe with all the loggers if you want a “global” configuration).

Then you could use an “appender filter” to make an appender called only if its an error message.

The only potential issue is contacting the spring bean from log4j2 appender. Read this SO thread to understand how technically you can achieve that.

The benefit of this method is that you don't change the framework but instead leverage the configuration options that it already provides.