Using Cache in Play Framework

I'm trying to implement a quiz application. The application loads the questions with ajax one by one. When a user clicks the 'to next question' button his/her answer is saved in cache. But when I debug, cache list is always null...

This code creates the first cache array:

public static void viewQuiz(@Required String user, @Required String test) {        
        if(validation.hasErrors()) {
            flash.error("Hoop kullanıcı lazım…");
            index();
        } else{
            TestClass selectedTest = TestClass.find("title", test).first();
            List<String> choiceList = new ArrayList<String>();
            session.put("testID", selectedTest.id);
            Cache.set("choices", choiceList, "30mn");
            render();
        }
    }

And this code is trying to save the answers one by one:

public static void question(@Required Long id, S开发者_如何转开发tring answer){
    Long testId = Long.parseLong(session.get("testID"));
    TestClass test = TestClass.findById(testId);
    List<Question> questList = Question.find("test_id", test.id.intValue()).fetch(); 
    Question quest = questList.get(id.intValue());
    if(answer != null){
        List<String> choiceList= Cache.get("choices",List.class);
        choiceList.add(id.intValue(), answer);
        Cache.set("choices", choiceList, "30mn");
    }   
    int count = questList.size()-1; 
    render(quest, count, id);
}

And this code is the html view of the second:

 #{extends 'main.html' /}

#{set title:'question.html' /}

<script type="text/javascript"> 
        var questionId = ${id};
        $('#nextButton').click(function(){
        $('#questionDiv').html('<p><img id = "loaderGif" src="public/images/loading.gif"/></p>');

        $('#questionDiv').load("/test/" + ++questionId);

    });
    $('#endButton').click(function(){
        $('#questionDiv').html('<p><img id = "loaderGif" src="public/images/loading.gif"/></p>');
        $('#questionDiv').load("/result");
    });
 </script> 

<legend>Soru ${id+1}</legend>
<p>&{quest.question}</p>

#{list items:quest.choices, as:'choice'} 
<p><input type="radio" name = "answer" id = "answer" size="30" value="${choice}"/>&{choice}</p>
#{/list}
#{if id < count}
<input id = "nextButton" name="nextButton" type="button" value="İleri"/>
#{/if}
#{else}
<input id = "endButton" name="endButton" type="button" value="Bitti"/>
#{/else}

Don't use the cache to 'store' objects. Either store it in the session or create a new model to store the answers. Generally, you cannot expect the cache to retain the objects you put into; it's a cache, not a store.

To quote from the Play! website: http://www.playframework.org/documentation/1.2.2/cache

It is important to understand that the cache contract is clear: when you put data in a cache, you can’t expect that data to remain there forever. In fact you shouldn’t. A cache is fast, but values expire, and the cache generally exists only in memory (without persistent backup).

Cache is not reliable and you may get it as null in dev mode. This is expected and you can try changing it to prod mode and see its behavior.