Hi
Type is really powerful but has one drawback: it is not working out of the
box. This means we need to add a reflect package with basic implementations
of some types in the api to make it a smooth api - at least
ParameterizedType and maybe a list/set/map ones cause it is very common.
Next issue we could hit is then we depend in the api of the jvm indirectly
- interfaces get new method with jvm versions sometimes so what we can do
is really bound to a jvm.
That said i like the fact it avoids to introduce a new api and yet another
type literal but just some common helper classes.
- Romain
Le 12 mars 2015 18:53, "Inderjeet Singh" <inder_at_alumni.stanford.edu> a
écrit :
> For Gson, we started with Type for pretty much the same reasons. Also
> because most developers are familiar with Type, and TypeLiteral is a
> new/advanced concept.
>
> Gson uses <T> T fromJson(String, Type) to avoid the need for casting. But
> it is unsafe, as you point out.
> In practice though, I have not seen it to be a problem.
>
> TypeLiteral are very useful in JSON conversion, so we did end up adding it
> to Gson. Once we added it, I would have liked to revise fromJson() methods
> to use TypeLiterals instead of Type. But we couldn't do that for backward
> compatibility reasons.
>
> So, the point really is that if TypeLiterals are going to be added in a
> JSR, then it is better for JsonB to depend on that JSR and use TypeLiterals.
>
> But if you can't depend on the TypeLiteral JSR (if any), then go ahead and
> use Type. It works just fine.
>
> Inder
>
>
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>
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>
>
> On Thu, Mar 12, 2015 at 9:51 AM, Eugen Cepoi <cepoi.eugen_at_gmail.com>
> wrote:
>
>> Hey Martin,
>>
>> 2015-03-12 17:21 GMT+01:00 Martin Vojtek <voytoo_at_gmail.com>:
>>
>>> Hi Experts,
>>>
>>> I would like to open discussion about Generic Type Support in JSON
>>> Binding.
>>>
>>> The initial proposal is to add two methods to Jsonb interface:
>>>
>>> public <T> T fromJson(String str, java.lang.reflect.Type runtimeType)
>>> throws JsonbException;
>>>
>>> public String toJson(Object object, java.lang.reflect.Type runtimeType)
>>> throws JsonbException;
>>>
>>> (and analogically other methods with different input/output)
>>>
>>> Based on reviewing existing options, it does not appear there is a
>>> single optimal option.
>>>
>>> Reasoning behind java.lang.reflect.Type.
>>>
>>> There are several ways how to deal with generics:
>>>
>>> 1. To use java.lang.reflect.Type
>>> 2. Use Type Literal (e.g. GenericType ...)
>>> 3. Use Generic Type Builder
>>>
>>> It would be a lot of unnecessary code to build Generic Type Builder. And
>>> I think this should be not part of JSON Binding.
>>>
>>>
>> I agree with you.
>>
>>
>>> Type Literal may work in some cases, but generally it doesn't work (in
>>> infinite cases). It is also not backed by Java Language Specification and
>>> may not work in the future. For example, Type Literal doesn't work when
>>> used with lambdas or with some JVM languages different than Java.
>>>
>>
>> I understand but I think that it works in most use cases where it is
>> needed. People use it to just deal with basic generics (custom or std
>> types).
>>
>>
>>> I don't want to introduce yet another GenericType class and to duplicate
>>> code with some other specifications.
>>>
>>
>> I agree it is ugly :( would have been better if there was a similar thing
>> as TypeToken from guava in std java (even if it is a hack in some way).
>>
>>
>>>
>>> Use of java.lang.reflect.Type seems like the best choice from bad
>>> choices available. Integration with JAX-RS will be flawless, it is upon the
>>> user to build java.lang.reflect.Type (hopefully with the help of JSON
>>> Binding implementation).
>>>
>> User can use already available Type Literal classes available in the Java
>>> ecosystem.
>>>
>>
>> Good point and most people already use guava. Only downside will be the
>> untyped result of the fromJson.
>> Here we can avoid user cast by doing : <T> T fromJson(String, Type), but
>> it is definitely unsafe.
>>
>> Might be interesting to have Inderjeets feedback on how it was when they
>> were using type and TypeToken.
>>
>>
>>>
>>> Examples and pdf proposal are available at
>>>
>>>
>>> https://java.net/projects/jsonb-spec/sources/git/content/spec/spec.pdf?rev=da7db533076856699cec49a4eebd300b9f4a7230
>>>
>>>
>>> https://github.com/json-binding/spec/blob/default_mapping/examples/runtime/src/main/java/examples/mapping/DefaultMappingGenerics.java
>>>
>>> Looking forward to your feedback.
>>>
>>> MartinV
>>>
>>
>>
>