JSTL 遍历列表创建字段集

Question

大家好，我目前正在遍历一个列表，并根据它们是否符合特定条件对字段集进行硬编码。如何编写一个循环来创建基于lidst 中所有组名的字段集，并使用与该组名一起动态出现的所有相应显示名称填充该字段集。我目前对此进行硬编码。

<%@ include file="../include/pre-header.html" %>

    <tr>
        <th>
            <span onclick="toggleDiv('displayFields', 'displayImg')" style="cursor: hand;">Data Fields&nbsp;<img name="displayImg" src="../images/minus.gif" /></span>
        </th>

    </tr>

    <tr>
        <td>

            <div id="displayFields" style="display:block;">
            <fieldset class="det">
                <legend>Header Data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'HEADER_DATA'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                            <br/>
                        </c:if>
                   </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Materiel Data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'MATERIEL_DATA'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                            <br/>
                        </c:if>
                    </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Planned Unit Data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'PLANNED_DATA'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                            <br/>
                        </c:if>
                    </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Actual Unit Data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'ACTUAL_DATA'}">
                <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                            <br/>
                        </c:if>
                </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Planned Cost Data</legend>
                <c:forEach var="detBean" items="${detFields}">
                    <c:if test="${detBean.groupName == 'COST_DATA'}">
                        <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                        <br/>
                    </c:if>
                </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Carry Over Data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'CARRYOVER_DATA'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                        <br/>
                        </c:if>
                    </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>Schedule Exceptions</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'SCHEDULE_EXCEPTIONS'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                        <br/>
                        </c:if>
                    </c:forEach>
            </fieldset>

            <fieldset class="det">
                <legend>DIFMS data</legend>
                    <c:forEach var="detBean" items="${detFields}">
                        <c:if test="${detBean.groupName == 'DIFMS_DATA'}">
                    <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
                        <br/>
                        </c:if>
                    </c:forEach>
            </fieldset>
            </div>
            <tr>
            <td style="text-align: center;">
            <input type="button" name="clear_choice"  value="Check All" onclick="checkUncheck(true);"/>
            &nbsp;&nbsp;&nbsp;&nbsp;
            <input type="button" name="clear_choice"  value="Uncheck All" onclick="checkUncheck(false);"/>

            </td>
            </tr>

        </td>
        </tr>

Answer 1

我建议将您的数据结构从 List<DetBean> 更改为 Map<String, List<DetBean>>，其中组名是映射键。

下面的例子展示了如何转换它：

Map<String, List<DetBean>> detFieldMap = new LinkedHashMap<String, List<DetBean>>();

for (DetBean detBean : detFields) {
    String groupName = detBean.getGroupName();
    List<DetBean> detBeans = detFieldMap.get(groupName);

    if (detBeans == null) {
        detBeans = new ArrayList<DetBean>();
        detFieldMap.put(groupName, detBeans);
    }

    detBeans.add(detBean);
}

request.setAttribute("detFieldMap", detFieldMap);

（您当然也可以在创建原始detFields 列表时更改数据结构）

您可能还想维护所有标题名称的映射

Map<String, String> detFieldHeaders = new HashMap<String, String>();
detFieldHeaderMap.put("HEADER_DATA", "Header Data");
detFieldHeaderMap.put("MATERIEL_DATA", "Materiel Data");
// ...

request.setAttribute("detFieldHeaders", detFieldHeaders);

（最好在 webapp 启动时创建一次并存储在应用程序范围内，您可以为此使用 ServletContextListener）

这样您就可以使用单个嵌套的<c:forEach>。对 Map 的每次迭代都会返回 Map.Entry ，而后者又具有 getKey() 和 getValue() 方法。键是String 组名，值是List<DetBean>。

<c:forEach items="${detFieldMap}" var="detFieldEntry">
    <fieldset class="det">
        <legend>${detFieldHeaders[detFieldEntry.key]}</legend>
        <c:forEach items="${detFieldEntry.value}" var="detBean">
            <input type="checkbox" name="fieldNames" value="${detBean.fieldName}">${detBean.displayName}</input>
            <br/>
        </c:forEach>
    </fieldset>
</c:forEach>