播放2.5：在自定义http操作中获取响应正文

Question

I'm trying to create a custom http action ( https://playframework.com/documentation/2.5.x/JavaActionsComposition ) to log request and response bodies with Play 2.5.0 Java. This is what I've got so far:

public class Log extends play.mvc.Action.Simple {

    public CompletionStage<Result> call(Http.Context ctx) {
        CompletionStage<Result> response = delegate.call(ctx);
        //request body is fine
        System.out.println(ctx.request().body().asText())
        //how to get response body string here while also not sabotaging http response flow of the framework?
        //my guess is it should be somehow possible to access it below?
        response.thenApply( r -> {
            //???
            return null;
        });
        return response;
    }

}

Answer 1

Logging is often considered a cross-cutting feature. In such cases the preferred way to do this in Play is to use Filters:

The filter API is intended for cross cutting concerns that are applied indiscriminately to all routes. For example, here are some common use cases for filters:

• Logging/metrics collection
• GZIP encoding
• Security headers

---

This works for me:

import java.util.concurrent.CompletionStage;
import java.util.function.Function;
import javax.inject.Inject;
import akka.stream.*;
import play.Logger;
import play.mvc.*;

public class LoggingFilter extends Filter {

    Materializer mat;

    @Inject
    public LoggingFilter(Materializer mat) {
        super(mat);
        this.mat = mat;
    }

    @Override
    public CompletionStage<Result> apply(
            Function<Http.RequestHeader, CompletionStage<Result>> nextFilter,
            Http.RequestHeader requestHeader) {
        long startTime = System.currentTimeMillis();
        return nextFilter.apply(requestHeader).thenApply(result -> {
            long endTime = System.currentTimeMillis();
            long requestTime = endTime - startTime;

            Logger.info("{} {} took {}ms and returned {}",
                requestHeader.method(), requestHeader.uri(), requestTime, result.status());
            akka.util.ByteString body = play.core.j.JavaResultExtractor.getBody(result, 10000l, mat);
            Logger.info(body.decodeString("UTF-8"));

            return result.withHeader("Request-Time", "" + requestTime);
        });
    }
}

What is it doing?

First this creates a new Filter which can be used along with other filters you may have. In order to get the body of the response we actually use the nextFilter - once we have the response we can then get the body.

As of Play 2.5 Akka Streams are the weapon of choice. This means that once you use the JavaResultExtractor , you will get a ByteString , which you then have to decode in order to get the real string underneath.

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Please keep in mind that there should be no problem in copying this logic in the Action that you are creating. I just chose the option with Filter because of the reason stated at the top of my post.