jstl: 无法解析表达式 [${item.class.name == 'List'}]

Question

下面的 jstl 代码应该基于此控制器方法解析 json 文件：

控制器

@RequestMapping(value="listagem.json", method=RequestMethod.GET)
@PreAuthorize("hasPermission(#user, 'listagem_'+#this.this.name)")
public ModelAndView listagem_json(@RequestParam("pagina") String pagina, @RequestParam("items") String items, @RequestParam("ordem") String ordem) {
    ModelAndView mav = new ModelAndView();

    mav.setViewName("listagem");        
    mav.addObject("lista", serv.listagem(pagina, items, ordem));
    mav.addObject("map", serv.getListaAtributos());

    return mav;
}

jstl代码

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib prefix="json" uri="http://www.atg.com/taglibs/json" %>
<json:object>
    <json:array name="item" var="item" items="${lista}">
          <json:object>
            <c:forEach var="attr" items="${map}">
                <c:choose>
                    <c:when test="${empty attr.value}">
                        <json:property name="${attr.key}" value="${item[attr.key]}"/>
                    </c:when>
                    <c:otherwise>
                        <c:choose>
                            <c:when test="${item.class.name == 'List'}">
                                <json:array name="${attr.key}" var="attr2" items="${item[attr.key]}">
                                    <json:object>
                                        <c:forEach var="attr3" items="${attr.value}">
                                            <json:property name="${attr3}" value="${attr2[attr3]}"/>
                                        </c:forEach>
                                    </json:object>
                                </json:array>
                            </c:when>
                            <c:otherwise>
                                <json:array name="${attr.key}">
                                    <json:object>
                                        <c:forEach var="attr2" items="${attr.value}">
                                            <c:set value="${attr.key}" var="object"/>
                                            <json:property name="${attr2}" value="${object}.${attr2}"/>
                                        </c:forEach>
                                    </json:object>
                                </json:array>
                            </c:otherwise>
                        </c:choose>
                    </c:otherwise>
                </c:choose>
            </c:forEach>
          </json:object>
    </json:array>
</json:object>

但是当我运行应用程序并请求 json 文件时，会发生此错误：

org.apache.jasper.JasperException: /WEB-INF/json/listagem.jsp (line: 13, column: 9) "${item.class.name == 'List'}" contains invalid expression(s): javax.el.ELException: Failed to parse the expression [${item.class.name == 'List'}]

任何人都可以告诉我编写此表达式的正确方法是什么${item.class.name == 'List'}以实现预期结果？

Answer 1

您可以使用这两个之一：

${item.getClass().simpleName == "List"} 
${item['class'].simpleName == "List"}

有关更多详细信息，请参阅此帖子