play framework - bind enum in routes

Question

I am building an app in java on play 2.2.

I have a java enum as a parameter in a function that I use in routes.

This is my enum class. I searched around and found out I need to implements QueryStringBindable to use it in routes.

public enum Something implements QueryStringBindable<Something> {
    a,
    b,
    c;

    @Override
    public F.Option<ClientStatus> bind(String key, Map<String, String[]> params) {
        String[] arr = params.get(key);
        if (arr == null || arr.length == 0) {
            return F.Option.None();
        } else {
            Something status = Something.valueOf(arr[0]);
            return F.Option.Some(status);
        }
    }

    @Override
    public String unbind(String key) {
        return null;
    }

    @Override
    public String javascriptUnbind() {
        return null;
    }
}

Yet I tried in my routes:

GET    /someurl     controllers.Application.function(status: util.enums.Something)

But it returns bad request with error message as:

For request 'GET /someurl' [util.enums.Something]

I googled and didn't find any answer working in my case. Did I miss something or play doesn't support binding enums?

Aquaplane

Answer 1

I had the same problem and I finally found out that it is not solvable as is.

By reading the documentation for PathBindable and QueryStringBindable I found that play framework requires the Bindable to provide a No Argument public constructor. Which by definition is no possible with enum in Java.

So I had to wrap my enum to solve this. In your example we would have something like:

public enum Something {
    a,
    b,
    c;

    public static class Bound implements QueryStringBindable<Bound>{
       private Something value;

        @Override
        public F.Option<ClientStatus> bind(String key, Map<String, String[]> params) {
            String[] arr = params.get(key);
            if (arr != null && arr.lenght > 0) {
                this.value = Something.valueOf(arr[0]);
                return F.Option.Some(this);
            } else {
                return F.Option.None();
            }
        }

        @Override
        public String unbind(String key) {
            return this.value.name();
        }

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

       public Something value(){
           return this.value;
       }
    }
}

and then you have to use the type some.package.Something.Bound as a type in your routes file.

EDIT: using that in a template is slightly more tricky. And you have to know a bit of scala. To follow @Aleksei's comment

<a href="@routes.MyController.showStuff(myEnumVar)">link</a>

should become

<a href="@{
   routes.MyController.showStuff(new MyEnumVarWrapper(myEnumVar)).url
}">link</a>

Photoreceptor

i gave a thought about the same solution, but it sounds too hacky to me. so i ended up binding the field to a string and parse the string in my controller to get a enum. This hacky solution is the closest for play 2, though. – Aquaplane

This way seems more work but at least you play framework takes care of returning the right http error code for you if someone gets the spelling wrong. – Photoreceptor

Your solution is not quite clear when one need to call action from template. I mean the code like this: <a href="@routes.MyController.showStuff(myEnumVar)">link</a> What I need to place instead of myEnumVar? – Leprose

Answer 2

I want to offer a small correction to the answer: (The return type isn't ClientStatus, and the unbind function should use the key parameter, it's for the url generatiion)

public enum Something {
a,
b,
c;

public static class Bound implements QueryStringBindable<Bound>{
   private Something value;

    @Override
    public F.Option<Bound> bind(String key, Map<String, String[]> params) {
        String[] arr = params.get(key);
        if (arr != null && arr.lenght > 0) {
            this.value = Something.valueOf(arr[0]);
            return F.Option.Some(this);
        } else {
            return F.Option.None();
        }
    }

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

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

   public Something value(){
       return this.value;
   }
}

}

Cowitch

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