一个弄了好久的问题，jar的版本问题

springmvc +tiles 启动后会报一个空指针异常 但是页面一刷新又能正常显示 异常是这样的
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException

 at java.lang.Thread.run(Unknown Source) 
 at org.apache.commons.digester.Digester.parse(Digester.java:1887)
 at org.apache.tiles.definition.digester.DigesterDefinitionsReader.read(DigesterDefinitionsReader.java:329)
 at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
 at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
 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:191)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
 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:298)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
...........后面就不复制了。
 at java.lang.Thread.run(Unknown Source) 

我之前也是找了好久，单看异常信息很难发现建议使用log4j打印日志，
log4j 内容如下:
log4j.rootLogger=DEBUG,A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%d %5p %t - %m%n
在web.xml配置如下:

<context-param>  
    <param-name>log4jConfigLocation</param-name>  
    <param-value>/WEB-INF/log4j.properties</param-value>  
</context-param>  

<context-param>  
    <param-name>log4jRefreshInterval</param-name>  
    <param-value>60000</param-value>  
</context-param>  

    <listener-class>  
        org.springframework.web.util.Log4jConfigListener  
    </listener-class>  
</listener>  

注意 slf4j-log4j12-1.6.2.jar , slf4j-api-1.6.2.jar ,jcl-over-slf4j-1.6.2.jar这几个jar版本问题。
此时报的异常时:java.lang.UnsupportedOperationException: This parser does not support specification “null” version “null”。
经过查找发现 原来是xercesImpl.jar版本过低的原因。我升级为xercesImpl-2.9.1.jar就行了。