严重: Servlet.service() for servlet [jsp] in context with path [/xxx] threw exception

严重: Servlet.service() for servlet [jsp] in context with path [/maven-ssm] threw exception [java.lang.NullPointerException] with root cause java.lang.NullPointerException
at org.apache.jsp.list_jsp._jspInit(list_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.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118)
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:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocolAbstractConnectionHandler.process(AbstractProtocol.java:603)atorg.apache.tomcat.util.net.JIoEndpointAbstractConnectionHandler.process(AbstractProtocol.java:603) at org.apache.tomcat.util.net.JIoEndpointAbstractConnectionHandler.process(AbstractProtocol.java:603)atorg.apache.tomcat.util.net.JIoEndpointSocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

这种情况是由于Maven配置了tomcat，但是没有在Maven项目中导入jsp-api的jar包的时候，此时eclipse会报错，导入jar包之后eclipse不会报错，但运行的时候会自动把tomcat中jsp-api和javax.servlet-api一起导入，导致jar包重复了，就会出现如上问题。
 

解决办法：在pom.xml文件下修改jsp-api的坐标如下

<dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>jsp-api</artifactId>
    <version>2.2</version>
    <scope>provided</scope>   <!-- 配置这一项，运行的时候不会重复导入jsp-api的jar包 -->
</dependency>
同样javax.servlet-api的坐标也需要配置<scope>provided</scope>

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>${servlet.version}</version>
    <scope>provided</scope> <!-- 配置这一项，运行的时候不会重复导入servlet-api的jar包 -->
</dependency>