java.lang.LinkageError: loader constraints violated when linking javax/el/ExpressionFactory class

严重: Servlet.service() for servlet jsp threw exception
java.lang.LinkageError: loader constraints violated when linking javax/el/ExpressionFactory class
 at org.apache.jsp.login_jsp._jspInit(login_jsp.java:23)
 at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
 at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:159)
 at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:329)
 at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
 at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
 at java.lang.Thread.run(Thread.java:595)

解释：
加载时违背约束条件。

错误的原因:
tomcat/lib下的el-api.jar与项目WEB-INF/lib目录下的el-api.jar冲突。

解决方式：
把项目目录下的el-api.jar删除即可。