Dynamic form and data binding with Spring MVC

Question

In my Spring MVC application I need to implement a dynamic questionnaire form: I have N questions and for each I have 3 options.

So in my page I'll have something like this:

|    Question 1   |   1   |   2   |   3   |
|    Question 2   |   1   |   2   |   3   |
|    Question 3   |   1   |   2   |   3   |
|    ...          |   1   |   2   |   3   |
|    Question N   |   1   |   2   |   3   |

Questions are stored in a database and for the options I'll use radio buttons. I'll use a forEach tag to creare dynamic rows, but I don't know how to post data and handle ModelAttribute binding in this scenario...

Which could be a good structure for my model attribute class? Is it possible to use binding for a dynamic form with Spring MVC?

Answer 1

how to post data and handle ModelAttribute binding in this scenario

you can do,

i am considering Question class like:

public class Question {
    private String question;
    private Map<Integer,Option> optionMap;
    private Integer selectedOptionKey;
        //getters and setters
}

and Option class like:

public class Option {

    private Integer optionKey;
    private String optionText;

    //getters and setters
}

and one QuestionsModel class for form binding like:

public class QuestionsModel {
    private Map<Integer, Question> questionMap;
    //getters and setters
}

and inside Controller class GET handler method, populate questions for example:

@RequestMapping(method=RequestMethod.GET)
    public String index(Model model){                
    Option optionA = new Option(1, "A");
    Option optionB = new Option(2, "B");
    Option optionC = new Option(3, "C");

    Map<Integer, Option> optionMap = new HashMap<Integer, Option>();
    optionMap.put(optionA.getOptionKey(),optionA);
    optionMap.put(optionB.getOptionKey(),optionB);
    optionMap.put(optionC.getOptionKey(),optionC);

    Question question1 = new Question("A Q", optionMap, 1);
    Question question2 = new Question("B Q", optionMap, 1);
    Question question3 = new Question("C Q", optionMap, 1);
    Map<Integer, Question> questionMap = new HashMap<Integer, Question>();
    questionMap.put(1, question1);
    questionMap.put(2, question2);
    questionMap.put(3, question3);

    model.addAttribute("questionsModel", new QuestionsModel(questionMap));

    return "index";
}

finally in jsp page use <form:hidden.. to keep old values, and render form elements like:

<c:url value="/questionPost" var="postUrl"/>

<form:form action="${postUrl}" modelAttribute="questionsModel" method="post">
    <table>
    <tr>
        <th>Question</th>
        <th>Options</th>        
    </tr>   
    <c:forEach items="${questionsModel.questionMap}" var="currQue" varStatus="queIndex">
        <tr>
            <td>
                <form:hidden path="questionMap[${queIndex.count}].question"/>
                <label>Question:</label><c:out value="${currQue.value.question}"/><br/>
            </td>
            <td>
            <c:forEach items="${currQue.value.optionMap}" var="opt" varStatus="optionIndex">
                <form:hidden path="questionMap[${queIndex.count}].optionMap[${optionIndex.count}].optionText"/>
                <form:hidden path="questionMap[${queIndex.count}].optionMap[${optionIndex.count}].optionKey"/>

                <form:radiobutton path="questionMap[${queIndex.count}].selectedOptionKey"
                    value="${opt.value.optionKey}" label="${opt.value.optionText}"/>

            </c:forEach>

             </td>
        </tr>
    </c:forEach>
    </table>
    <input type="submit"/>
</form:form>

you can receive binding and model in POST like:

@RequestMapping(value="/questionPost", method=RequestMethod.POST)
public String indexPost(@ModelAttribute("questionsModel") QuestionsModel questionModel, BindingResult result){
    System.out.println(questionModel.getQuestionMap());

    return "redirect:/";
} 

Answer 2

This class is my model attribute:

public class Questionnaire {
    private List<Question> questions = new ArrayList<>();
    private List<Answer> answers = new ArrayList<>();

    // set + get
}

And:

public class Question {
    private int id;
    private String text;

    // set+ get

}

public class Answer {
    private int questionId;
    private int value;

    // set + get
}

I populate questions list before I put it into model.

In my page I use this code:

<c:forEach items="${questionnaire.questions}" var="question"
    varStatus="gridRow">
    <div>
    ${question.text} 
        <s:bind path="questionnaire.answers[${gridRow.index}].questionID">
            <input type="hidden" name="${status.expression}"
                id="${status.expression}" value="${question.id}" />
        </s:bind>
        <s:bind path="questionnaire.answers[${gridRow.index}].value">
            <sf:radiobuttons path="${status.expression}"
                items="${radio_button_options}" />
        </s:bind>
    </div>
</c:forEach>

Posting this form I get a fully populated questionnaire instance in my controller.

NOTE I found this post very helpful to solve my problem.