Question

I’m learning myself Play 2.0 (Java API used) and would like to have a double/float parameter (for location coordinates), something like http://myfooapp.com/events/find?latitude=25.123456&longitude=60.251253.

I can do this by getting the parameters as String and parsing them at controller etc but can I use automatic binding here?

Now, I first tried simply having one double value:

GET     /events/foo                 controllers.Application.foo(doublevalue: Double)

with

public static Result foo(Double doublevalue) {
    return ok(index.render("Foo:" + doublevalue));
}

What I got was “No QueryString binder found for type Double. Try to implement an implicit QueryStringBindable for this type.”

Have I missed something already provided or
do I have to make a custom QueryStringBindable that parses Double?

I found some instructions on making a custom string query string binder with Scala at http://julien.richard-foy.fr/blog/2012/04/09/how-to-implement-a-custom-pathbindable-with-play-2/

What I tried:

I implemented DoubleBinder at package binders:

import java.util.Map;
import play.libs.F.Option;
import play.mvc.QueryStringBindable;

public class DoubleBinder implements QueryStringBindable<Double>{

    @Override
    public Option<Double> bind(String key, Map<String, String[]> data) {
        String[] value = data.get(key);
        if(value == null || value.length == 0) {
            return Option.None();
        } else {
            return Option.Some(Double.parseDouble(value[0]));
        }
    }

    @Override
    public String javascriptUnbind() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public String unbind(String key) {
        // TODO Auto-generated method stub
        return null;
    }
}

And tried to add it to project/Build.scala’s main:

routesImport += "binders._"

but same result : “No QueryString binder found for type Double….”

• I also changed the routing signature to java.lang.Double but that didn’t help either
• I also changed the DoubleBinder to implement play.api.mvc.QueryStringBindable (instead of play.mvc.QueryStringBindable) both with Double & java.lang.Double at the routing signature but no help still

Answer 1

Currently (in Play 2.0), Java binders only work with self-recursive types. That is, types looking like the following:

class Foo extends QueryStringBindable<Foo> {
  …
}

So, if you want to define a binder for java.lang.Double, which is an existing type of Java, you need to wrap it in a self-recursive type. For example:

package util;

public class DoubleW implements QueryStringBindable<DoubleW> {

    public Double value = null;

    @Override
    public Option<DoubleW> bind(String key, Map<String, String[]> data) {
        String[] vs = data.get(key);
        if (vs != null && vs.length > 0) {
            String v = vs[0];
            value = Double.parseDouble(v);
            return F.Some(this);
        }
        return F.None();
    }

    @Override
    public String unbind(String key) {
        return key + "=" + value;
    }

    @Override
    public String javascriptUnbind() {
         return value.toString();
    }

}

Then you can use it as follows in your application:

GET    /foo     controllers.Application.action(d: util.DoubleW)

public static Result action(DoubleW d) {
      …
}