Question

I’m writing a database log4j appender in Play.

On its append() method, it creates a new instance of a model entity Log4jLine, and saves() it via JPA.

This works fine on debug/info logs. However, exceptions are not logged.
There is a call to this appender from framework code, but I suspect it is not working because the JPA session is not valid at this point.

How would I adapt the code to support this use case?

public class DBAppender extends AppenderSkeleton {
    @Override
    protected void append(LoggingEvent loggingEvent) {
        Log4jLine logLine = new Log4jLine(...);
        logLine.save();
    }
}

Answer 1

Per our conversation above I was curious about how to do this and was able to get this to work. Essentially, you need to create a new EntityManager and fully manage it yourself. Calling any of the Play built-ins (.save(), .merge(), etc) will cause them to use the EntityManager that Play sets up for you. However, if you revert to standard JPA calls, it will work.

// Mapped in routes file as GET /exception        
public static void exceptionTest() {
    RuntimeException e = new RuntimeException("This is a test");
    logException(e);
    renderText("You are here");

}

private static void logException(RuntimeException e) {
    EntityManager em = JPA.newEntityManager();
    Notification n = new Notification();
    n.setMessage(e.getMessage());

    em.getTransaction().begin();
    em.persist(n);
    em.getTransaction().commit();
    throw e;
}

This is just a quick and dirty experiment to prove the point. You’ll obviously need to handle exceptions and failure cases in logException() that I’m not handling. And just for clarity, Notification is a basic object in my project I was able to use for this quickly.

Hope that helps!