当我们在tomcat 8.5上使用Spring boot初始化器将Spring 4.3升级到5时，我们开始出现异常。
2021-06-06 12:37:50,482 DEBUG [background-preinit] messageinterpolation.ResourceBundleMessageInterpolator (ResourceBundleMessageInterpolator.java:220) - Failed to load expression factory via classloader ParallelWebappClassLoader
context: ROOT
delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76f856a8
javax.el.ELException: Unable to find ExpressionFactory of type [# Licensed to the Apache Software Foundation (ASF) under one or more]
at javax.el.ExpressionFactory.newInstance(ExpressionFactory.java:154) ~[el-api.jar:3.0.FR]
at javax.el.ExpressionFactory.newInstance(ExpressionFactory.java:93) ~[el-api.jar:3.0.FR]
at org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator.canLoadExpressionFactory(ResourceBundleMessageInterpolator.java:216) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator.buildExpressionFactory(ResourceBundleMessageInterpolator.java:170) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator.<init>(ResourceBundleMessageInterpolator.java:94) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.internal.engine.AbstractConfigurationImpl.getDefaultMessageInterpolator(AbstractConfigurationImpl.java:573) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.internal.engine.AbstractConfigurationImpl.getDefaultMessageInterpolatorConfiguredWithClassLoader(AbstractConfigurationImpl.java:822) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.internal.engine.AbstractConfigurationImpl.getMessageInterpolator(AbstractConfigurationImpl.java:483) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.internal.engine.ValidatorFactoryImpl.<init>(ValidatorFactoryImpl.java:153) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.HibernateValidator.buildValidatorFactory(HibernateValidator.java:38) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.hibernate.validator.internal.engine.AbstractConfigurationImpl.buildValidatorFactory(AbstractConfigurationImpl.java:451) [hibernate-validator-6.2.0.Final.jar:6.2.0.Final]
at org.springframework.boot.autoconfigure.BackgroundPreinitializer$ValidationInitializer.run(BackgroundPreinitializer.java:149) [spring-boot-autoconfigure-2.5.0.jar:2.5.0]
at org.springframework.boot.autoconfigure.BackgroundPreinitializer$1.runSafely(BackgroundPreinitializer.java:111) [spring-boot-autoconfigure-2.5.0.jar:2.5.0]
at org.springframework.boot.autoconfigure.BackgroundPreinitializer$1.run(BackgroundPreinitializer.java:102) [spring-boot-autoconfigure-2.5.0.jar:2.5.0]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_151]
Caused by: java.lang.ClassNotFoundException: # Licensed to the Apache Software Foundation (ASF) under one or more
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1358) ~[catalina.jar:8.5.50]
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1180) ~[catalina.jar:8.5.50]
at javax.el.ExpressionFactory.newInstance(ExpressionFactory.java:147) ~[el-api.jar:3.0.FR]
... 14 more
el-api jar来自tomcat/lib，我们也把el-api的版本从2改成了3，但还是出现了这个异常。
对于这个异常，有什么已知的解决方案吗？
它可以被忽略吗？
我发现了相关的bug，它不会被修复。
EPEL el6在2020-11-30变成了报废（EOL）状态。EPEL el6不再被维护，这意味着它将不会收到任何进一步的安全或错误修复更新。因此，我们正在关闭这个错误。
StackOverflow：java - Spring migration 4.3 to 5 on tomcat 8.5 el-api error - Stack Overflow