Play 2.2.x Java MDC Filter

[Diego Mole]

Hi! I'm trying without success to create a "filter" or "interceptor" or something that make me able to catch every request, read the cookie and set MDC key-value for logging purposes. And when the request has finish, clear those keys, in order not to leave zombie MDC values on that thread.

I found a few examples in the web, but none of them works in this play version (2.2.x for Java).

The only one that compile and work was this: http://www.ivanmartinvalle.com/2015/04/12/play-framework-java-filters/

But this filter only do something when the request arrives, but not when the request is leaving... 

JavaFilter.java

import play.api.mvc.*;
import scala.Function1;
import scala.concurrent.Future;
import scala.runtime.AbstractFunction1;


public abstract class JavaFilter implements Filter {


    @Override
    public Future<SimpleResult> apply(Function1<RequestHeader, Future<SimpleResult>> nextFilter, RequestHeader requestHeader) {
        return nextFilter
                .apply(requestHeader)
                .map(new AbstractFunction1<SimpleResult, SimpleResult>() {
                    @Override
                    public SimpleResult apply(SimpleResult currentResult) {
                        return Apply(currentResult, requestHeader);
                    }
                },
                        play.api.libs.concurrent.Execution.defaultContext());
    }


    @Override
    public EssentialAction apply(EssentialAction next) {
        return Filter$class.apply(this, next);
    }


    public abstract SimpleResult Apply(SimpleResult currentResult, RequestHeader requestHeader);
}

LoggerMdcFilter.java

import org.jboss.logging.MDC;
import play.api.mvc.RequestHeader;
import play.api.mvc.SimpleResult;


public class LoggerMdcFilter extends JavaFilter {


    @Override
    public SimpleResult Apply(SimpleResult currentResult, RequestHeader requestHeader) {
        MDC.put("email", requestHeader.session().get("email").get());
        return currentResult;
        //TODO: Clean MDC when request ends
    }


}

Can anyone share a working example of setting and clear an MDC on play 2.2.x for Java? 

Or at least tell me if the given example can be improve in order to clean the MDC when the request leaves the server?

Thanks in advance!

Diego

[Greg Methvin]

Hi Diego,

The Java filter implementation you have doesn't really do the same thing as its Scala equivalent. Typically a filter would take the "next" action to call so it can wrap the entire call. Here's the implementation from 2.5.x: https://github.com/playframework/playframework/blob/2.5.x/framework/src/play/src/main/java/play/mvc/Filter.java.

Also, you're going to run into problems with MDC because it uses a thread local. To get around that you could explicitly pass an SLF4J Marker, or try one of the workarounds here: https://yanns.github.io/blog/2014/05/04/slf4j-mapped-diagnostic-context-mdc-with-play-framework/

Greg

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[Diego Mole]

Hi Greg! Thanks for your answer. 

I couldn't make the filter example work in play 2.2.x ... I think there are components that are only present in play 2.5.x

Anyway, I found and example in the web that fulfill my needs:

@Override
    public Action onRequest(Request request, Method actionMethod) {
        return new Action.Simple() {
            @Override
            public F.Promise<SimpleResult> call(Http.Context ctx) throws Throwable {


                MDC.put("username", ctx.session().get("email"));
                F.Promise<SimpleResult> result = delegate.call(ctx);


                MDC.remove("username");
                return result;
            }
        };
    }

This code works well... but it doesn't prevent the "Thread-Local" problem that you told me. And the example you gave me is in Scala... do you have another working example in Java for Play 2.2x?

Thanks in advance!

Diego

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[Greg Methvin]

Hi Diego,

You should be able to use the first solution provided in the blog post (a custom Akka dispatcher) in a Java app as well. Play's default execution context is also used to execute Java actions and in the F.Promise implementation, so I think that should cover all your needs. The Dispatcher API in Akka is the same for Java and Scala.

Greg

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[Greg Methvin]

I'd also suggest you consider simply explicitly passing the logger around and use a library like https://github.com/godaddy/godaddy-logger

So instead of calling the logger statically you could pass logger.with(request) that already has a request identifier. That does mean you have to explicitly pass something around, but it's less likely to cause problems if you happen to call some code that doesn't use the default execution context.

Greg