How to assign keys and values of the map - the property of a modelAttribute object in JSP forms using Spring?

Question

I have a questionnary web app in Spring. Here is the code of getting form with questions and answer options and returning it to exam.jsp, :

@RequestMapping(value = "/")
public String getExam(ModelMap map) {

    List<Question> questions = new ArrayList<Question>();
    // Here I am getting the all data for questions list
    // and basically I am sending to the view the list of questions, where each question has list of variants
    map.addAttribute("questions", questions);
    return "exam";
}

My model classes:

public class Question {
    private int id;
    private String text;
    private List<Variant> variants;

    //getters and setters
}

public class Variant {
    private int id;
    private int questionId;
    private int correctness;
    private String text;

    //getters and setters
}

public class AnswerSheetWrapper {
    Map<Integer, Integer> answerSheet;

    //getter and setter
}

In my exam.jsp: I am getting questions attribute from controllers getExam method. I am creating radiobutton groups for each question and filling in modelattribute 'answerSheetWrapper' (Maybe I am doing it incorrect, so please tell me how to do it). I want the map 'answerSheet' to hold question id's as keys and variant id's as values:

<form:form action="/exam/calculate" modelAttribute="answerSheetWrapper">
    <c:forEach items="${questions}" var="question">
        ${question.text}<br />
        <c:forEach items="${question.variants}" var="variant">
            <form:radiobutton path="answerSheet['${question.id}']" value="${variant.id}"/>${variant.text} <!--Here code throws Exception when runned-->
        </c:forEach>
        <br />
    </c:forEach>
    <input type="submit" value="Göndər"/>
</form:form>

And this is my controller method where form action takes place:

@RequestMapping(value = "/exam/calculate")
public String calculate(@ModelAttribute("answerSheetWrapper")AnswerSheetWrapper answerSheetWrapper) {

    // do processing with modelAttribute object
    return "someView";
}

I am not sure if I specify the path in form:radiobutton correctly.

When I am running the app I receive:

HTTP Status 500 - An exception occurred processing JSP page /resources/pages/exam.jsp at line 29

The root cause is:

java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'answerSheetWrapper' available as request attribute

So where is the problem in my code? Any help is appreciated.

Answer 1

It seems like you forgot to add the answerSheetWrapper to the model. Currently you are adding just the questions, so modify your controller code like this:

map.addAttribute("questions", questions);
map.addAttribute("answerSheetWrapper", new AnswerSheetWrapper());

Also this

<form:radiobutton path="answerSheet['${question.id}']"
                  value="${variant.id}"/>${variant.text}

would probably be better written using the label attribute of form:radiobutton

<form:radiobutton path="answerSheet['${question.id}']"
                  value="${variant.id}" label="${variant.text}" />