我希望某些元素只在前端显示给某些用户（而不是任何具有特定角色的用户）。
为什么这样做有效：

<form sec:authorize="${principal.username.equals('A') }" th:action="@{'/saunojat/' + ${saunoja.username} + '/photo'}" method="POST" enctype="multipart/form-data">
    <input type="file" name="photo" />
    <p>Kuvan tarina: <input type="text" name="description"/></p>
    <p> Asetetaanko kuva profiilikuvaksi?<input type="checkbox" name="isProfilepicture"/></p>
    <input type="submit" value="Send!"/>
</form>

但这并不是：

<form sec:authorize="${principal.username.equals(saunoja.username) }" th:action="@{'/saunojat/' + ${saunoja.username} + '/photo'}" method="POST" enctype="multipart/form-data">
    <input type="file" name="photo" />
    <p>Kuvan tarina: <input type="text" name="description"/></p>
    <p> Asetetaanko kuva profiilikuvaksi?<input type="checkbox" name="isProfilepicture"/></p>
    <input type="submit" value="Send!"/>
</form>

Sanoja是模型中的一个属性。它是一个@实体：

package projekti;

import java.util.List;
import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.jpa.domain.AbstractPersistable;

@Entity
@AllArgsConstructor
@NoArgsConstructor
@Data
public class Saunoja extends AbstractPersistable<Long> {

    private String username;

    private String password;

    private String firstName;

    private String lastName;

    @ElementCollection(targetClass = String.class, fetch = FetchType.EAGER)
    private List<String> roles;

}

错误：
白标签错误页此应用程序没有/error的显式Map，因此您将其视为回退。
7月20日星期二15:14:09 eest 2021发生意外错误（类型=内部服务器错误，状态=500）。模板解析期间发生错误（模板：“类路径资源[templates/Sanoja.html]”）org.thymeleaf.exceptions.templateinputexception:模板解析期间发生错误（模板：“类路径资源[templates/Sanoja.html]”）org.thymeleaf.templateparser.markup.abstractmarkuptemplateparser.parse（abstractmarkuptemplateparser.java:241）位于org.thymeleaf.templateparser.markup.abstractmarkuptemplateparser.parsestandalone（abstractmarkuptemplateparser.java:100）位于org.thymeleaf.engine.templatemanager.parseandprocess（templatemanager.java:666）位于org.thymeleaf.templateengine.process（templateengine.java:1098）在org.thymeleaf.templateengine.process（templateengine.java:1072）在org.thymeleaf.spring5.view.thymeleafview.renderfragment（thymeleafview.java:362）在org.thymeleaf.spring5.view.thymeleafview.thymeleafview.render（thymeleafview.java:189）在org.springframework.web.servlet.dispatcherservlet.render（dispatcherservlet.java:1373）位于org.springframework.web.servlet.dispatcherservlet.processdispatchresult（dispatcherservlet.java:1118）位于org.springframework.web.servlet.dispatcherservlet.dodispatch（dispatcherservlet.java:1057）位于org.springframework.web.servlet.dispatcherservlet.doservice（dispatcherservlet.java:943）在org.springframework.web.servlet.frameworkservlet.processrequest（frameworkservlet.java:1006）在org.springframework.web.servlet.frameworkservlet.doget（frameworkservlet.java:898）在javax.servlet.http.httpservlet.service（httpservlet.java:626）在org.springframework.web.servlet.frameworkservlet.service（frameworkservlet.java:883）在javax.servlet.http.httpservlet.service（httpservlet.java:733）在org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:231）在org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）在org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:193）org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）上的org.apache.tomcat.websocket.server.wsfilter.dofilter（wsfilter.java:53）位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:320）位于org.springframework.security.web.access.intercept.filtersecurityinterceptor.invoke（filtersecurityinterceptor.java:126）位于org.springframework.security.web.access.intercept.filtersecurityinterceptor.dofilter（filtersecurityinterceptor.java:90）位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334），位于org.springframework.security.web.access.exceptiontranslationfilter.dofilter（exceptiontranslationfilter.java:118），位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filter ChainProxy.java:334）org.springframework.security.web.session.sessionmanagementfilter.dofilter（sessionmanagementfilter.java:137）在org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）在org.springframework.security.web.authentication.anonymousauthenticationfilter.dofilter（anonymousauthenticationfilter.java:111）在org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.servletapi.securitycontextholderawarerequestfilter.dofilter（securitycontextholderawarerequestfilter.java:158）org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.savedrequest.requestcacheawrefilter.dofilter（requestcacheawrefilter.java:63）位于org.springframework.security.web.filterchainproxy$virtualfilter.dofilter（filter.java:334）位于org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）org.springframework.security.ui.defaultlogoutpagegeneratingfilter.dofilterinternal（defaultlogoutpagegeneratingfilter.java:52）org.springframework.security.web.filterchainproxy$VirtualFilterChainProxy.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.authentication.ui.defaultloginpagegeneratingfilter.dofilter（defaultloginpagegeneratingfilter.java:216），位于org.springframework.security.web.authentication.abstractauthenticationprocessingfilter.dofilter（abstractauthenticationprocessingfilter.java:200）位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.authentication.logout.logoutfilter.dofilter（logoutfilter.java:116）位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.header.headerwriterfilter.doheadersafter（headerwriterfilter.java:92）位于org.springframework.security.web.header.headerwriterfilter.dofilternel（headerwriterfilter.java:77）位于org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）位于org.springframework.security.web.filterchainproxy$virtualfilter.dofilter（filter-chainproxy.java:334）位于org.springframework.security.web.context.securitycontextpersistencefilter.dofilter（securitycontextpersistencefilter.java:105）位于org.springframework.security.web.filterchainproxy$virtualfilterchain.dofilter（filterchainproxy.java:334）位于org.springframework.security.web.context.request.async.webasyncmanagerintegrationfilter.dofilternel（webasyncmanagerintegrationfilter.java:56）位于org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）位于org.springframework.security.web.filterchainproxy$virtualfilter.dofilter（filter.java:334）位于org.springframework.security.web.filterchainproxy.dofilterinternal（filterchainproxy.java:215），位于org.springframework.security.web.filterchainproxy.dofilter（filterchainproxy.java:178），位于org.springframework.web.filter.delegatingfilterproxy.invokedelegate（delegatingfilterproxy.java:358）org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:193）org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）上的org.springframework.web.filter.delegatingfilterproxy.dofilter（delegatingfilterchain.java:271）org.springframework.web.filter.requestcontextfilter.dofilterinternal（requestcontextfilter.java:100）位于org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）位于org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:193）位于org.springframework.web.filter.formcontentfilter.dofilterinternal（formcontentfilter.java:93）org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）的org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）位于org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:193）位于org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）位于org.apache.catalina.core.applicationfilterchain.internaldofilter（applicationfilterchain.java:193）org.apache.catalina.core.applicationfilterchain.dofilter（applicationfilterchain.java:166）的org.springframework.web.filter.onceperrequestfilter.dofilter（onceperrequestfilter.java:119）位于org.apache.catalina.core.standardwrappervalve.invoke（standardwrappervalve.java:202）在org.apache.catalina.core.standardcontextvalve.invoke（standardcontextvalve.java:96）在org.apache.catalina.authenticator.authenticatorbase.invoke（authenticatorbase.java:541）在org.apache.catalina.core.standardhostvalve.invoke（standardhostvalve.java:139）在org.apache.catalina.valves.errorreportvalve.invoke（errorreportvalve.java:92）在org.apache.catalina.core.standardenginevalve.invoke（standardenginevalve.java:74）在org.apache.catalina.connector.coyoteadapter.service（coyoteadapter.java:343）在org.apache.coyote.http11.http11processor.service（http11processor.java:373）在org.apache.coyote.abstractprocessorlight.process（abstractprocessorlight.java:65）在org.apache.coyote.abstractprotocol$connectionhandler.process（abstractprotocol.java:868）在org.apache.tomcat.util.net.socketprocessorbase.run（socketprocessorbase.java:49）在java.base/java.util.concurrent.threadpoolexecutor.runworker（threadpoolexecutor.java:1128）在java.base/java.util.concurrent.threadpoolexecutor$worker.run（threadpoolexecutor.java:628）在org.apache.tomcat.util.threads.taskthread$WrappingRun.run（taskthread.java:61）在java.base/java.lang.thread.run（thread:834）上的javaorg.attoparser.parseexception:执行处理器“org.thymeleaf.extras.springsecurity5.dial.processor.authorizeattrprocessor”时出错（模板：“Sanoja”-第58行，第15列）位于org.attoparser.markupparser.parsedocument（markupparser.java:393）位于org.attoparser.markupparser.parse（markupparser.java:257）位于org.thymeleaf.templateparser.markup.abstractmarkuptemplateparser.parse（abstractmarkuptemplateparser.java:230）。。。86更多原因：org.thymeleaf.exceptions.templateprocessingexception:处理器“org.thymeleaf.extras.springsecurity5.dial.processor.authorizeattrprocessor”（模板：“Sanoja”-第58行，col 15）位于org.thymeleaf.processor.element.abstractattributetagprocessor.doprocess（abstractattributetagprocessor.java:117）的org.thymeleaf.processor