关于tomcat启动web时classloader加载el实现类报错的解决方式

1.严重: Servlet.service() for servlet [jsp] in context with path [/web] threw exception [java.lang.LinkageError: loader constraint violation: when resolving interface method 2."javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of 3.the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for resolved class, 4.javax/servlet/jsp/JspApplicationContext, have different Class objects for the type avax/el/ExpressionFactory; used in the signature] with root cause
5.java.lang.LinkageError: loader constraint violation: when resolving interface method 6."javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of 7.the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for resolved class, 8.javax/servlet/jsp/JspApplicationContext, have different Class objects for the type avax/el/ExpressionFactory; used in the signature
at org.apache.jsp.index_jsp._jspInit(index_jsp.java:31)
at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:49)
at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:180)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

at java.lang.Thread.run(Thread.java:745)

一开始没有仔细阅读异常信息，以为是tomcat版本不对或者其它情况，后来仔细的检查了一下异常信息，第8行：have different Class objects for the type avax/el/ExpressionFactory; used in the signature，  这句话说的是，classLoader在加载ExpressionFactory这个接口的实现的时候发现有多个实现类，所以报错了。既然是这样那就来maven的依赖关系中来找一找关于el的类，

果然发现在我们的依赖中有依赖el相关的包，所以在maven的pom中需要把它们排除

<dependency>
<groupId>com.msfinance.demo</groupId>
<artifactId>demo-biz</artifactId>
<exclusions>
<exclusion>
<artifactId>javax.el-api</artifactId>
<groupId>javax.el</groupId>
</exclusion>
<exclusion>
<artifactId>javax.el</artifactId>
<groupId>org.glassfish.web</groupId>
</exclusion>
</exclusions>
</dependency>

这样再次打包运行，就OK了。