java - Thymeleaf Map Form Binding

Question

db.html

<div th:each="pr, stat: *{mergeMap}">
    <tr>
        <td><input type="text" name="key" th:value="${pr.key}" /></td>
        <td><input type="text" name="value" th:value="${pr.value}" /></td>
    </tr>
</div>

On submitting this input, i always get mergeMap to be empty at the Spring Controller. What should be done to get the value of mergeMap?

Controller.java

@RequestMapping(value = "/shot")
    public String saveMergeProducts(@ModelAttribute(value="prod") MergedProductInfoDTO prod, BindingResult bindingResult, 
            Model model, HttpServletRequest request) {
        System.out.println(prod.toString());
        return "forward:/backoffice/db";
    }

HTML

<form action="#" th:action="@{shot}" method="POST" th:object="${prod}">
            <tr>
            <td><span th:text="${index.index}"></span></td>
                <td><input type="text" name="id" th:value="*{id}" th:readonly="readonly" /></td>
                <td><input type="text" name="categoryName" th:value="*{categoryName}" th:readonly="readonly" /></td>
                <td><input type="text" name="subCategoryName" th:value="*{subCategoryName}" th:readonly="readonly" /></td>
                <td><input type="text" name="productBrand" th:value="*{productBrand}" /></td>
                <td><input type="text" name="productSubBrand" th:value="*{productSubBrand}" /></td>
                <td><input type="text" name="series" th:value="*{series}" /></td>
                <td><input type="text" name="model" th:value="*{model}" /></td>
            </tr>
        <tr>
            <td colspan="7">
                            <tr>
                                <th>KEY</th>
                                <th>VALUE</th>
                            </tr>
                            <div th:each="pr, stat: *{mergeMap}">
                                <tr>
                                    <td><input type="text" name="mergeMapKey" th:value="${pr.key}" /></td>
                                    <td><input type="text" name="mergeMapValue" th:value="${pr.value}" /></td>
                                </tr>
                            </div>
                        </table>
                    </td>
                    <td><input type="text" name="tags" th:value="*{tags}" /></td>
                    <td><input type="submit" value="Submit" /></td>
                </tr>

Answer 1

To access the Map property of the form-backing bean, use the __${...}__ preprocessor

<div th:each="pr, stat: *{mergeMap}">
    <tr>
        <td><input type="text" name="value" th:value="${pr.key}" readonly="true"/></td>
        <td><input type="text" name="value" th:field="*{mergeMap[__${pr.key}__]}"/></td>
    </tr>
</div>

What it does it evaluates the inner expression first before evaluating the whole expression. Note that in this case, ${pr.key} should not be modified so that the update will be reflected to the map property of the bean bound to the form.

Reference : http://www.thymeleaf.org/doc/tutorials/2.1/thymeleafspring.html#dynamic-fields