jsp - 无法在 JSP 中获取模型属性的大小
问题描述
这是我使用 jsp 的第一个项目,我正在尝试构建一个表格,其中每一行看起来有点像这样
在最后一列(喜欢)中,目前只有一个按钮,但我想在它旁边显示喜欢的数量。
这是我的问题。当我尝试使用jsp函数长度时${fn:length(mes.likes)}
我得到以下异常
org.apache.jasper.JasperException: javax.el.ELException: Problems calling function [fn:length]
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:606)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:482)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:170)
org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:314)
org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1325)
org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1069)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1008)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:870)
javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:119)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:158)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:100)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215)
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270)
我从HomeController加载模型中的所有消息
@Controller
public class HomeController {
@Autowired
IMessageService messageService;
@GetMapping("/homepage")
public String index(Model model) {
List<MessageEntity> messages = messageService.getAll();
model.addAttribute("allMessages", messages);
return "index";
}
}
这是MessageEntity类
public class MessageEntity{
private int Id;
private String title;
private String content;
private Date createdAt;
private User createdBy;
private List<LikeEntity> likes;
}
最后,这是我在index.jsp文件中显示信息的表格。
<table id="panneau">
<thead class="bg-dark text-light">
<tr>
<th>Message</th>
<th>Emetteur</th>
<th>Date/heure</th>
<th>Likes</th>
</tr>
</thead>
<tbody class="text-black">
<c:forEach var="mes" items="${allMessages}">
<tr id="message${mes.id}">
<td>
<div><b>${mes.title}</b></div>
<div>${mes.content}</div>
</td>
<td>
<c:choose>
<c:when test="${mes.anonymous}">
anonyme
</c:when>
<c:otherwise>
${mes.createdBy.firstName} ${mes.createdBy.lastName}
</c:otherwise>
</c:choose>
</td>
<td>
${mes.createdAt}
</td>
<td>
<div>${fn:length(mes.likes)}</div>
<div><button class="btn btn-dark" id="like${mes.id}"><i class="far fa-thumbs-up fa-2x"></i></button></div>
</td>
</tr>
</c:forEach>
</tbody>
</table>
当我删除${fn:length(mes.likes)}
时,一切正常,但我需要一种方法来获取这些信息。
我看过其他类似的问题,但似乎没有一个能解决我的问题。
顺便说一句,我确实<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
在文件的开头
编辑
这是likeEntity类
import javax.persistence.*;
import java.util.Objects;
/**
* Created by owner on 18-05-07.
*/
@Entity
@Table(name = "likes", schema = "heroku_9efd0238a94d992")
public class LikeEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "like_id", nullable = false)
private int id;
@Basic
@Column(name = "is_dislike", nullable = true)
private Boolean isDislike;
@ManyToOne(cascade = {
CascadeType.MERGE,
CascadeType.PERSIST,
CascadeType.DETACH,
CascadeType.REFRESH,
})
@JoinColumn(name = "liked_by")
private UserEntity likedBy;
@ManyToOne(cascade = {
CascadeType.MERGE,
CascadeType.PERSIST,
CascadeType.DETACH,
CascadeType.REFRESH,
})
@JoinColumn(name = "liked_message")
private MessageEntity likedMessage;
public LikeEntity() {
this.setDislike(false);
}
}
解决方案
Disclamer:这是一种解决方法,而不是真正的解决方案
我仍然不知道为什么喜欢不能延迟加载,但是将 fetchtype 从延迟更改为渴望似乎已经成功了......
我知道这个解决方案不是最优的。就我而言,这种解决方法是合适的,因为它只是一个学校项目,所以我永远不会在一条消息上获得成千上万的赞。
但是,如果您使用大量数据,我认为此解决方案不合适。
推荐阅读
- git - Semantic-Release - 预发布版本不增加补丁、次要或主要版本
- r - 如何在 dplyr 中获取 case_when 接受字符的条件
- amazon-web-services - 是否可以为文件建立 AWS CodeCommit 策略?
- swift - 使用 Swift 获取已安装应用程序的特定信息
- c# - Newtonsoft JSON反序列化问题
- pipeline - 如何自动刷新大三角帆管道的控制台输出
- python - 如何获取多个图像的轮廓区域并在数据框中分离
- google-apps-script - /auth/classroom.topics.readonly 是敏感范围吗?
- excel - 从另一个工作簿隐藏工作表
- swift - 如何在 NSTextView 周围绘制边框