Tomcat部署CAS Overlay与CAS Management时Jackson冲突致启动故障

• 已完成Tomcat 9.0.41运行环境搭建
• 先构建cas-overlay-template 6.3项目，将生成的cas.war放入Tomcat的webapps目录启动，所有功能运行正常
• 后续构建cas-management-overlay 6.3项目，将生成的cas-management.war放入同一webapps目录，重启Tomcat加载应用时启动失败

2021-01-22 20:39:04,641 WARN [org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext] - <Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'formContentFilter' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.boot.web.servlet.filter.OrderedFormContentFilter]: Factory method 'formContentFilter' threw exception; nested exception is java.lang.NoSuchMethodError: 'com.fasterxml.jackson.databind.cfg.MutableCoercionConfig com.fasterxml.jackson.dataformat.xml.XmlMapper.coercionConfigDefaults()'>
2021-01-22 20:39:04,666 ERROR [org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter] - <

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APPLICATION FAILED TO START
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Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    com.fasterxml.jackson.dataformat.xml.XmlMapper.<init>(XmlMapper.java:175)

The following method did not exist:

    'com.fasterxml.jackson.databind.cfg.MutableCoercionConfig com.fasterxml.jackson.dataformat.xml.XmlMapper.coercionConfigDefaults()'

The method's class, com.fasterxml.jackson.dataformat.xml.XmlMapper, is available from the following locations:

    jar:file:/opt/cas/tomcat-9.0.41/webapps/cas-management/WEB-INF/lib/jackson-dataformat-xml-2.12.0.jar!/com/fasterxml/jackson/dataformat/xml/XmlMapper.class

The class hierarchy was loaded from the following locations:

    com.fasterxml.jackson.dataformat.xml.XmlMapper: file:/opt/cas/tomcat-9.0.41/webapps/cas-management/WEB-INF/lib/jackson-dataformat-xml-2.12.0.jar
    com.fasterxml.jackson.databind.ObjectMapper: file:/opt/cas/tomcat-9.0.41/webapps/cas-management/WEB-INF/lib/jackson-databind-2.11.3.jar
    com.fasterxml.jackson.core.ObjectCodec: file:/opt/cas/tomcat-9.0.41/webapps/cas-management/WEB-INF/lib/jackson-core-2.11.3.jar
    com.fasterxml.jackson.core.TreeCodec: file:/opt/cas/tomcat-9.0.41/webapps/cas-management/WEB-INF/lib/jackson-core-2.11.3.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of com.fasterxml.jackson.dataformat.xml.XmlMapper

• 报错本质是Jackson生态组件的版本错位不兼容：
  • 位于cas-management/WEB-INF/lib目录下的jackson-dataformat-xml-2.12.0.jar，其内部的XmlMapper初始化逻辑需要调用jackson-databind 2.12.x版本才新增的coercionConfigDefaults()方法
  • 但同目录下实际加载的jackson-databind、jackson-core版本为2.11.3，不存在上述新增方法，最终触发NoSuchMethodError导致应用启动失败
• 已部署的cas主应用不受影响的原因：Tomcat对每个web应用采用独立类加载隔离机制，cas应用本身的Jackson依赖版本是自洽兼容的，不会和cas-management的依赖版本产生交叉干扰

• 优先方案：在cas-management-overlay项目的构建配置中，强制统一所有Jackson相关组件的版本，与已存在的jackson-dataformat-xml-2.12.0.jar对齐，将jackson-databind、jackson-core、jackson-annotations的版本全部锁定为2.12.0，重新构建生成war包后重新部署
• 临时快速修复方案：无需重新构建项目，直接将cas-management/WEB-INF/lib目录下的jackson-dataformat-xml-2.12.0.jar替换为2.11.3版本，与目录内现有jackson-databind、jackson-core的版本完全对齐，替换完成后重启Tomcat即可
• 操作注意事项：
  • 所有依赖版本调整操作，必须限定在对应web应用的WEB-INF/lib目录内完成
  • 不要将调整后的Jar包放入Tomcat公共lib目录，避免跨应用类加载冲突

内容的提问来源于stack exchange，提问作者Tch