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Vincent Buzzano  
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 More options Jul 15 2010, 11:52 am
From: Vincent Buzzano <vincent.buzz...@gmail.com>
Date: Thu, 15 Jul 2010 08:52:36 -0700 (PDT)
Local: Thurs, Jul 15 2010 11:52 am
Subject: Scala renderJSON
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Hello,

I get a problem using Scala and trying to do a renderJSON on a list

I get all contacts and then try to render the list as JSON

> var contacts = asScala[Contact].findAll
> renderJSON(contacts)

I get this exception

Execution exception (In /app/controllers/Contacts.scala around line
48)
UnsupportedOperationException occured : Expecting parameterized type,
got class scala.collection.immutable.$colon$colon.  Are you missing
the use of TypeToken idiom?  See
http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and...

play.exceptions.JavaExecutionException: Expecting parameterized type,
got class scala.collection.immutable.$colon$colon.
 Are you missing the use of TypeToken idiom?
 See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and...
        at play.mvc.ActionInvoker.invoke(ActionInvoker.java:259)
        at Invocation.HTTP Request(Play!)
Caused by: java.lang.UnsupportedOperationException: Expecting
parameterized type, got class scala.collection.immutable.$colon$colon.
 Are you missing the use of TypeToken idiom?
 See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and...
        at com.google.gson.TypeInfoFactory.getActualType(TypeInfoFactory.java:
97)
        at
com.google.gson.TypeInfoFactory.extractRealTypes(TypeInfoFactory.java:
116)
        at com.google.gson.TypeInfoFactory.getActualType(TypeInfoFactory.java:
65)
        at
com.google.gson.TypeInfoFactory.getTypeInfoForField(TypeInfoFactory.java:
54)
        at
com.google.gson.ObjectNavigator.navigateClassFields(ObjectNavigator.java:
148)
        at com.google.gson.ObjectNavigator.accept(ObjectNavigator.java:123)
        at
com.google.gson.JsonSerializationContextDefault.serialize(JsonSerialization ContextDefault.java:
56)
        at com.google.gson.Gson.toJsonTree(Gson.java:230)
        at com.google.gson.Gson.toJson(Gson.java:315)
        at com.google.gson.Gson.toJson(Gson.java:270)
        at com.google.gson.Gson.toJson(Gson.java:250)
        at play.mvc.results.RenderJson.<init>(RenderJson.java:20)
        at play.mvc.Controller.renderJSON(Controller.java:280)
        at play.mvc.ControllerDelegate.renderJSON(ControllerDelegate.java:58)
        at controllers.Contacts$.getContacts(/app/controllers/Contacts.scala:
48)
        at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:
374)
        at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:
357)
        at play.mvc.ActionInvoker.invoke(ActionInvoker.java:162)
        ... 1 more

it's work when i render only one contact

> var contacts = asScala[Contact].findAll
> renderJSON(contacts(0))

Do you have any idea ?

 
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Liu Yongjian  
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 More options Jul 15 2010, 12:08 pm
From: Liu Yongjian <ggd...@gmail.com>
Date: Fri, 16 Jul 2010 00:08:17 +0800
Local: Thurs, Jul 15 2010 12:08 pm
Subject: Re: [play-framework] Scala renderJSON
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I have the same question about that .

According to the gson document , you need to define a TypeToken  if the
object that your are serializing/deserializing is a ParameterizedType (i.e.
contains at least one type parameter and may be an array) then you must use
the toJson(Object,
Type)<file:///E:/libary/google-gson-1.4-release/google-gson-1.4/gson-1.4-ja vadoc/com/google/gson/Gson.html#toJson(java.lang.Object,
java.lang.reflect.Type)> or fromJson(String,
Type)<file:///E:/libary/google-gson-1.4-release/google-gson-1.4/gson-1.4-ja vadoc/com/google/gson/Gson.html#fromJson(java.lang.String,
java.lang.reflect.Type)> method.

Here is an example for serializing and deserialing a ParameterizedType
picked from gson docs:

 Type listType = new TypeToken<List<String>>() {}.getType();
 List<String> target = new LinkedList<String>();
 target.add("blah");

 Gson gson = new Gson();
 String json = gson.toJson(target, listType);
 List<String> target2 = gson.fromJson(json, listType);

But it does not work properly in scala.collection.immutable.List, so
you can only use array instead - it seams the array in Scala is the
same as the one in Java

On Thu, Jul 15, 2010 at 11:52 PM, Vincent Buzzano <vincent.buzz...@gmail.com


 
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dirk  
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 More options Dec 6 2010, 2:29 pm
From: dirk <australiandevelo...@gmail.com>
Date: Mon, 6 Dec 2010 16:29:21 -0300
Local: Mon, Dec 6 2010 2:29 pm
Subject: Re: [play-framework] Scala renderJSON
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> UnsupportedOperationException occured : Expecting parameterized type,
> got class scala.collection.immutable.$colon$colon. Are you missing
> the use of TypeToken idiom?

Here's a solution to the problem using a custom serializer:

// Your action
def search(query: String) = Json(MySerializer.toJson(User.find("name like
?", query)))

object MySerializer {
    val builder = new GsonBuilder()

builder.registerTypeAdapter(classOf[scala.collection.immutable.$colon$colon [_]],
new CollectionSerializer)
    val gson = builder.create

    def toJson(obj: Any) = gson.toJson(obj)

}

// Custom serializer
//
http://sites.google.com/site/gson/gson-user-guide#TOC-Custom-Serializ...
class CollectionSerializer extends
JsonSerializer[scala.collection.immutable.$colon$colon[_]] {
    override def serialize(items:
scala.collection.immutable.$colon$colon[_], objType: Type, context:
JsonSerializationContext): JsonElement = {
        val json = new JsonArray()
        items.foreach(item => json.add(context.serialize(item)))
        return json
    }


 
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Loic  
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 More options Apr 12 2011, 9:09 am
From: Loic <loic.desco...@gmail.com>
Date: Tue, 12 Apr 2011 06:09:22 -0700 (PDT)
Local: Tues, Apr 12 2011 9:09 am
Subject: Re: [play-framework] Scala renderJSON
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I have this  problem too, maybe we should open a bug


 
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Dirk  
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 More options Apr 12 2011, 10:40 am
From: Dirk <dirkm...@gmail.com>
Date: Tue, 12 Apr 2011 10:40:08 -0400
Local: Tues, Apr 12 2011 10:40 am
Subject: Re: [play-framework] Scala renderJSON
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I'm currently working on getting lift-json working with play/scala:
http://groups.google.com/group/play-framework/browse_thread/thread/dd...
http://groups.google.com/group/liftweb/browse_thread/thread/b6d5a0060...


 
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Loic  
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 More options Apr 13 2011, 3:49 am
From: Loic <loic.desco...@gmail.com>
Date: Wed, 13 Apr 2011 00:49:23 -0700 (PDT)
Local: Wed, Apr 13 2011 3:49 am
Subject: Re: [play-framework] Scala renderJSON
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There is a method for that in the play scala API, no need to use lift-json I
think.

According to the Scala module documentation, I guess this should work
without error :

def listByApi = Json(Contacts.findAll())

But it reponds an error :

{
    type:   'play.exceptions.JavaExecutionException',
    message: 'Expecting parameterized type, got class scala.collection.immutable.$colon$colon.
 Are you missing the use of TypeToken idiom?
 See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and...


 
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Guillaume Bort  
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 More options Apr 13 2011, 3:54 am
From: Guillaume Bort <guillaume.b...@gmail.com>
Date: Wed, 13 Apr 2011 09:54:24 +0200
Local: Wed, Apr 13 2011 3:54 am
Subject: Re: [play-framework] Scala renderJSON
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That why we need Lift-JSON. GSON is not able to serialize correctly scala
types.

--
Guillaume Bort, http://guillaume.bort.fr

 
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v6ak  
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 More options Apr 13 2011, 4:23 pm
From: v6ak <v...@volny.cz>
Date: Wed, 13 Apr 2011 13:23:57 -0700 (PDT)
Local: Wed, Apr 13 2011 4:23 pm
Subject: Re: Scala renderJSON
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It's simple:

import net.liftweb.json.ParameterNameReader
import java.lang.reflect.Constructor
import play.classloading.enhancers.LocalvariablesNamesEnhancer
import scala.collection.JavaConversions._

object PlayParameterReader extends ParameterNameReader{
        def lookupParameterNames(constructor: Constructor[_]) =
LocalvariablesNamesEnhancer.lookupParameterNames(constructor)

}

Then you need to use this paranamer instead of the default one in
Formats. There is one way that allows it:
https://gist.github.com/891235

Regards
Vít Šesták 'v6ak'

On Apr 12, 4:40 pm, Dirk <dirkm...@gmail.com> wrote:


 
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Guillaume Bort  
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 More options Apr 14 2011, 4:44 am
From: Guillaume Bort <guillaume.b...@gmail.com>
Date: Thu, 14 Apr 2011 10:44:50 +0200
Local: Thurs, Apr 14 2011 4:44 am
Subject: Re: [play-framework] Re: Scala renderJSON
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We really need Lift-JSON working with Play Scala as GSON won't work for most
Scala specific structure. If you have a working version, please send us a
pull request.

--
Guillaume Bort, http://guillaume.bort.fr

 
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Dirk  
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 More options Apr 15 2011, 12:33 pm
From: Dirk <dirkm...@gmail.com>
Date: Fri, 15 Apr 2011 13:33:10 -0300
Local: Fri, Apr 15 2011 12:33 pm
Subject: Re: [play-framework] Re: Scala renderJSON
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I'm almost there, just trying to iron out a few remaining issues with
lift-json. For example it wasn't able to correctly serialize a model object
until yesterday:
http://groups.google.com/group/liftweb/browse_thread/thread/96d3bd870...

On Thu, Apr 14, 2011 at 5:44 AM, Guillaume Bort <guillaume.b...@gmail.com>wrote:


 
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v6ak  
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 More options Apr 16 2011, 12:49 pm
From: v6ak <v...@volny.cz>
Date: Sat, 16 Apr 2011 09:49:06 -0700 (PDT)
Local: Sat, Apr 16 2011 12:49 pm
Subject: Re: [play-framework] Re: Scala renderJSON
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In fact, I don't have integrated it well. I just have solved the issue with
loading parameter names according to a dicsussion thread. The problem was
probably that Lift JSON expects serialized classes to be on classpath
(unless you provide a custom ParameterNameReader), but Play! uses a
different classloading mechanism. (This is possibly not true in the
production mode.)

I'm not sure about the right Play integration. Like any advanced
(de)serializer, Lift suports some configuration. (In fact, you can handle
polymorphism, of you configure it.) The configuration is described in an
instance of net.liftweb.json.Formats.

I've some ideas: https://gist.github.com/923233 (simple by default, complex
and robust on demand)

* Constructor parameter vs. method: Constructor parameter seems to be a
cleaner way for me.
* It is possible to use constructor overloading for convenience. So,
Controller can have constructors that accepts both of variants (either
net.liftweb.json.Formats or something like play.json.JsonAdapter).
* Combining availbility of constructor parameter and protected method seems
to be odd for me. Parameters could be overriden in such case by a trait. A
similar API design fail have been done in java.lang.Thread, which implements
java.lang.Runnable. Although there is a different issue (you can accidentaly
call run() instead of start()), both of these designs are crazy.
* Should Play! "defensively" force an instance of PlayParameterReader? There
are some advantages and disadvantages on both sides:
* * If Play! does not force the PlayParameterReader (or
PlayParameterNameReader), it can lead to some serialization issues (the
result of the serialization is "{}") if the user speciffies some non-default
Formats and does not choose to use PlayParameterReader.
* * If Play! forces the PlayParameterReader, it can lead to similar iussues
if user uses a specific ParameterNameReader on purpose. Fortunately, it is
an edge case. However, this seems to be a magic for me.
* * It is also possible to use one of these ParameterNameReader-s by default
and the other as a fallback, but there is still some magic.
* * It is also possible to allow user to switch overriding
ParameterNameReader off, which can be the best way.

What do you think about it?

Regards
Vít Šesták 'v6ak'


 
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Dirk  
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 More options Apr 16 2011, 9:15 pm
From: Dirk <dirkm...@gmail.com>
Date: Sat, 16 Apr 2011 22:15:30 -0300
Local: Sat, Apr 16 2011 9:15 pm
Subject: Re: [play-framework] Re: Scala renderJSON
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The reason they added the configuration option to use another parameter name
reader is because I asked for it so that lift-json could be used with play:
http://groups.google.com/group/liftweb/browse_thread/thread/b6d5a0060...
So we simply define a play ParameterNameReader that uses play's classloading
mechanism. I'll do this within the scala plugin itself so that play users
don't need to worry about it.
I'm currently working on it, but as I mentioned in my last post I'm just
waiting for them iron out a couple of problems with the serialization:
http://groups.google.com/group/liftweb/browse_thread/thread/96d3bd870...


 
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v6ak  
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 More options Apr 17 2011, 8:06 am
From: v6ak <v...@volny.cz>
Date: Sun, 17 Apr 2011 05:06:59 -0700 (PDT)
Local: Sun, Apr 17 2011 8:06 am
Subject: Re: [play-framework] Re: Scala renderJSON
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RI understand that Play users don't need to worry about it in simple cases. However, one may need a custom Formats (for typeHinth etc.). In such case, the behavior is a tradeoff between simplicity and magic.

Regards,
Vít Šesták 'v6ak'


 
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Dirk  
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 More options Apr 18 2011, 11:13 am
From: Dirk <dirkm...@gmail.com>
Date: Mon, 18 Apr 2011 12:13:00 -0300
Subject: Re: [play-framework] Re: Scala renderJSON
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Yes you're right the developer should be allowed to override the default
behaviour. I will make the Play ParameterNameReader object public so that it
can be re-used. In the case that the developer wants to use a completely
different library, he can produce the required json as a string and pass
that to Json()


 
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