Survey - Where do you use constraints on parameterized type?

by Emmanuel Bernard on 23 Nov 2016 feedback

For Bean Validation 2, we are working on the support for Collection<@Email String>, Optional<@Min(3) Integer> etc. This has been a very common request and with Java 8 type use support, we can how achieve this. However, we need your feedback on how you would use such feature.

Some context

We have support not only for collections, Optional, Java FX properties but also for what we call custom parameterized containers. We are wondering a few things about custom parameterized containers, namely how common they are. This will affect the trade-offs we want to make on the design of that feature.

What is a container?

A container is a type that wraps and exposes one or several values. The values is what you want to apply your constraints on. And the container is parameterized because at use site, you can declare what type it actually contains. For a Set<@Email String>, we want to make sure every string in the set is an email.

Another less obvious example is a tuple class.

public class Pair<V1,V2> {
    V1 getV1() { ... }
    V2 getV2(); { ... }

public class Address {
    // street1 is mandatory, street2 is optional
    // represented via a Pair object
    Pair<@NotNull @Size(max=250) String, @Size(max=250) String> streetFields;

Other examples are:

  • a tree structure containing specific object types

  • Guava’s Multimap (or any multimap for that matter)


We are wondering which type of parameterized containers you have in your code base and how likely you are going to apply constrains on their contained value. The form is a list of short questions that will help us get a better picture.

Here is the link to the form in a separate page or use it directly embedded below.

Many thanks!