Writing custom filters for Play! 2.2 in Java

Question

I have a simple scenario: automatically add a response header to every HTTP response; and I want to do this in Java.

Looking at src/play-filters-helpers/src/ma

Answer 1

There isn't a nice Java API available for creating Play Filters. However, you can adapt the existing Scala APIs into a nice Java template.

For example:

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

public abstract class JavaFilter implements Filter {

@Override
public Future apply(Function1> nextFilter, RequestHeader requestHeader) {
    return nextFilter
            .apply(requestHeader)
            .map(new AbstractFunction1() {
                     @Override
                     public Result apply(Result 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 Result Apply(Result currentResult, RequestHeader requestHeader);
}

Example implementation:

import play.api.mvc.RequestHeader;
import play.api.mvc.Result;

public class HelloFilter extends JavaFilter {

@Override
public Result Apply(Result currentResult, RequestHeader requestHeader) {
    if (requestHeader.headers().get("X-Filter").isDefined()) {
        ResultAdapter resultAdapter = new ResultAdapter(currentResult);
        return resultAdapter.WithHeader("X-Hello", "World!");
    }
    return currentResult;
  }
}

For a further explanation of how this works, see my blog post about it here