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

Unfortunately there isn't a good way to create and use Filters from Java yet. But you can do what you need pretty easily with Scala.

Create a new file app/filters/AddResponseHeader.scala containing:

package filters

import play.api.mvc._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

object AddResponseHeader extends Filter {
  def apply(f: (RequestHeader) => Future[SimpleResult])(rh: RequestHeader): Future[SimpleResult] = {
    val result = f(rh)
    result.map(_.withHeaders("FOO" -> "bar"))
  }
}

And create a new file app/Global.scala containing:

import filters.AddResponseHeader
import play.api.mvc.WithFilters

object Global extends WithFilters(AddResponseHeader)

That should apply a new response header to every response.

UPDATE: There is a way to use this in a Global.java file:

@Override
public <T extends EssentialFilter> Class<T>[] filters() {
    return new Class[] {AddResponseHeader.class};
}

And also change the object AddResponseHeader above to class AddResponseHeader.

Answer 2

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<Result> apply(Function1<RequestHeader, Future<Result>> nextFilter, RequestHeader requestHeader) {
    return nextFilter
            .apply(requestHeader)
            .map(new AbstractFunction1<Result, Result>() {
                     @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

Answer 3

To add a custom filter (MyFilter.class) create a Global.java file in the root package. Tested in PlayFramework 2.3.x and Java (JDK8)

import play.GlobalSettings;
import play.api.mvc.EssentialFilter;

public class Global extends GlobalSettings {
    @Override
    public <T extends EssentialFilter> Class<T>[] filters() {
        return new Class[]{MyFilter.class};
    }
}