Issue with Spring Boot 2.6.4 and Thymeleaf 3.0.15 causing TemplateProcessingException

[FrelliBB]

We recently upgraded our feature flag service to use Spring Boot 2.6.4 which has updated the Thymeleaf version to 3.0.15.

This has started causing rendering issues on the features page caused by a TemplateProcessingException. The full stack trace is below. We believe this might be related to this issue raised on the Thymeleaf project.

org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating OGNL expression: "feat.flippingStrategy.class.simpleName" (template: "features" - line 88, col 16)
	at org.thymeleaf.standard.expression.OGNLVariableExpressionEvaluator.evaluate(OGNLVariableExpressionEvaluator.java:201)
	at org.thymeleaf.standard.expression.OGNLVariableExpressionEvaluator.evaluate(OGNLVariableExpressionEvaluator.java:105)
	at org.thymeleaf.standard.expression.VariableExpression.executeVariableExpression(VariableExpression.java:166)
	at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:66)
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:109)
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:138)
	at org.thymeleaf.standard.processor.AbstractStandardExpressionAttributeTagProcessor.doProcess(AbstractStandardExpressionAttributeTagProcessor.java:144)
	at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74)
	at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95)
	at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633)
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleOpenElement(ProcessorTemplateHandler.java:1314)
	at org.thymeleaf.engine.OpenElementTag.beHandled(OpenElementTag.java:205)
	at org.thymeleaf.engine.Model.process(Model.java:282)
	at org.thymeleaf.engine.Model.process(Model.java:290)
	at org.thymeleaf.engine.IteratedGatheringModelProcessable.processIterationModel(IteratedGatheringModelProcessable.java:367)
	at org.thymeleaf.engine.IteratedGatheringModelProcessable.process(IteratedGatheringModelProcessable.java:221)
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleCloseElement(ProcessorTemplateHandler.java:1640)
	at org.thymeleaf.engine.CloseElementTag.beHandled(CloseElementTag.java:139)
	at org.thymeleaf.engine.TemplateModel.process(TemplateModel.java:136)
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:592)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1067)
	at org.ff4j.web.controller.AbstractController.get(AbstractController.java:189)
	at org.ff4j.web.FF4jDispatcherServlet.doGet(FF4jDispatcherServlet.java:68)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:655)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at datadog.trace.instrumentation.springweb.HandlerMappingResourceNameFilter.doFilterInternal(HandlerMappingResourceNameFilter.java:50)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:96)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:359)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:889)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1735)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Unknown Source)
Caused by: ognl.OgnlException: simpleName
	at ognl.ObjectPropertyAccessor.getPossibleProperty(ObjectPropertyAccessor.java:69)
	at ognl.ObjectPropertyAccessor.getProperty(ObjectPropertyAccessor.java:147)
	at ognl.OgnlRuntime.getProperty(OgnlRuntime.java:3236)
	at ognl.ASTProperty.getValueBody(ASTProperty.java:114)
	at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
	at ognl.SimpleNode.getValue(SimpleNode.java:258)
	at ognl.ASTChain.getValueBody(ASTChain.java:141)
	at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
	at ognl.SimpleNode.getValue(SimpleNode.java:258)
	at ognl.Ognl.getValue(Ognl.java:537)
	at ognl.Ognl.getValue(Ognl.java:501)
	at org.thymeleaf.standard.expression.OGNLVariableExpressionEvaluator.executeExpression(OGNLVariableExpressionEvaluator.java:336)
	at org.thymeleaf.standard.expression.OGNLVariableExpressionEvaluator.evaluate(OGNLVariableExpressionEvaluator.java:180)
	... 70 common frames omitted
Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Calling methods is forbidden for type 'java.lang.Class' in Thymeleaf expressions. Blacklisted classes are: [java.util.concurrent.RunnableFuture, java.util.concurrent.Executor, java.lang.Runtime, java.util.concurrent.FutureTask, java.util.concurrent.ListenableFuture, java.lang.Runnable, java.util.concurrent.Future, java.lang.Thread, java.lang.reflect.Executable, java.lang.Class, java.lang.ClassLoader, java.sql.DriverManager].
	at org.thymeleaf.standard.expression.OGNLVariableExpressionEvaluator$ThymeleafACLMemberAccess.isAccessible(OGNLVariableExpressionEvaluator.java:435)
	at ognl.OgnlRuntime.getMethodValue(OgnlRuntime.java:2077)
	at ognl.ObjectPropertyAccessor.getPossibleProperty(ObjectPropertyAccessor.java:60)
	... 82 common frames omitted

[mojo2012]

Downgrading to version thymeleaf 3.0.14.RELEASE helped:

<dependency>
	<groupId>org.ff4j</groupId>
	<artifactId>ff4j-spring-boot-starter</artifactId>
	<version>${ff4j.version}</version>
	<exclusions>
		<exclusion>
			<groupId>javax.servlet</groupId>
			<artifactId>servlet-api</artifactId>
		</exclusion>
		<exclusion>
			<groupId>org.thymeleaf</groupId>
			<artifactId>thymeleaf</artifactId>
		</exclusion>
	</exclusions>
</dependency>
<dependency>
	<groupId>org.thymeleaf</groupId>
	<artifactId>thymeleaf</artifactId>
	<version>3.0.14.RELEASE</version>
</dependency>

[mojo2012]

Will this ever be fixed?

[clun]

Good question... we are not responsible for Thymeleaf breaking changes, we would have appreciate a pull request.

• feat.flippingStrategy.class.simpleName get you the className of the current flip strategy. As this operation is not allowed anymore the object Feature need a dedicated getter getFlippingStrategyClassName().

• the template got updated with

 <b><span th:text="${feat.flippingStrategyClassName}">---</span></b>

Associated Commit