canal的使用錯誤“Context namespace element 'component-scan' and its parser class”

在繼上次爲了用canal發生意外之後，今日又被canal坑了一把。

在上次的CanalClient實現時，爲了測試方便，直接將CanalClient類放置於項目的Test中進行測試，同時加載了canal的maven依賴，然後就沒有繼續執行其他操作。今日啓動tomcat，發現無法正常啓動，啓動日誌出現一堆錯誤

org.springframework.beans.factory.BeanDefinitionStoreException: Unexpected exception parsing XML document from class path resource [spring-mybatis.xml]; nested exception is java.lang.IllegalStateException: Context namespace element 'component-scan' and its parser class [org.springframework.context.annotation.ComponentScanBeanDefinitionParser] are only available on JDK 1.5 and higher
    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:420) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:342) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:310) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:143) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:178) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:149) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:124) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:92) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:123) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:422) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:352) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255) ~[spring-2.5.6.jar:4.1.4.RELEASE]
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199) ~[spring-2.5.6.jar:4.1.4.RELEASE]
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:45) [spring-2.5.6.jar:4.1.4.RELEASE]
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5017) [catalina.jar:7.0.63]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5531) [catalina.jar:7.0.63]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [catalina.jar:7.0.63]
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901) [catalina.jar:7.0.63]
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877) [catalina.jar:7.0.63]
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:652) [catalina.jar:7.0.63]
    at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1809) [catalina.jar:7.0.63]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301) [tomcat-coyote.jar:7.0.63]
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) [na:1.8.0_45]
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) [na:1.8.0_45]
    at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:618) [catalina.jar:7.0.63]
    at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:565) [catalina.jar:7.0.63]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301) [tomcat-coyote.jar:7.0.63]
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) [na:1.8.0_45]
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) [na:1.8.0_45]
    at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1466) [na:1.8.0_45]
    at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76) [na:1.8.0_45]
    at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1307) [na:1.8.0_45]
    at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1399) [na:1.8.0_45]
    at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:828) [na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:323) [na:1.8.0_45]
    at sun.rmi.transport.Transport$1.run(Transport.java:200) [na:1.8.0_45]
    at sun.rmi.transport.Transport$1.run(Transport.java:197) [na:1.8.0_45]
    at java.security.AccessController.doPrivileged(Native Method) [na:1.8.0_45]
    at sun.rmi.transport.Transport.serviceCall(Transport.java:196) [na:1.8.0_45]
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568) [na:1.8.0_45]
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826) [na:1.8.0_45]
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$254(TCPTransport.java:683) [na:1.8.0_45]
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$2/1579453818.run(Unknown Source) [na:1.8.0_45]
    at java.security.AccessController.doPrivileged(Native Method) [na:1.8.0_45]
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682) [na:1.8.0_45]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
Caused by: java.lang.IllegalStateException: Context namespace element 'component-scan' and its parser class [org.springframework.context.annotation.ComponentScanBeanDefinitionParser] are only available on JDK 1.5 and higher
    at org.springframework.context.config.ContextNamespaceHandler$1.parse(ContextNamespaceHandler.java:65) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.NamespaceHandlerSupport.parse(NamespaceHandlerSupport.java:69) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1297) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1287) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:135) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:92) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions(XmlBeanDefinitionReader.java:507) ~[spring-2.5.6.jar:2.5.6]
    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:398) ~[spring-2.5.6.jar:2.5.6]
    ... 59 common frames omitted

受昨日意外影響，尋找一上午解決方案無果，下午仔細分析與可運行狀態時的區別，發現僅添加canal的maven依賴項。然後又觀測到錯誤中的spring-2.5.6.jar包，我在maven中使用的spring依賴都是4.1版本以上的，出現spring-2.5.6.jar包明顯有問題，可能是發生了包衝突。遂刪除canal的maven依賴項，spring-2.5.6.jar果然消失，所以證明canal依賴於spring的舊版本。

問題原因：canal依賴spring-2.5.6.jar舊版本，和新版本發生包衝突。

思考：在運行canal時，並不需要將canal置於項目中，可以使CanalClient獨立運行。它的功能和目的也相對獨立，就是爲了完成Redis和mysql間的數據同步。