Passing a Java callback in GWT to JSNI method which returns a Promise?

I am new to Promises and need some advice on how to handle a returned Promise in a JSNI method called from Java. Can't use JsInterop due to older version 2.7 of GWT. Any advice is appreciated.

Thanks for your time!

If you just have to read properties on the return object, you may try treating it as JSONObject.

Alternatively you could call a method of your Java object in the resolver function of the promise to check conditions to decide if you want to resolve/reject. p.then() could be called with onFulfilled/onRejected functions just wrapping Java method calls to handle the result.

Example:

public class PromiseWrapper {

    boolean evaluate(String value) {
        return value != null ? true : false;
    }

    void onFulfilled(String value) {
        // use value
    }

    void onRejected(Strin reason) {
        // use reason
    }

    public native void doSomethingAynchronously() /*-{
        var p = new Promise(
            function(resolve, reject) {
                var value = null; // Get value from somewhere
                if(this.@com.company.project.PromiseWrapper::evaluate(Ljava/lang/String;)(value)) {
                    resolve(value);
                }
                else {
                    reject("Because");
                }
            }
        );
        p.then(function(value) {
                this.@com.company.project.PromiseWrapper::onFulfilled(Ljava/lang/String;)(value);
            }, 
            function(reason) {
                this.@com.company.project.PromiseWrapper::onRejected(Ljava/lang/String;)(reason);
            }
        );
    }-*/;

}

This is an untested example.