Error allocating a servlet instance应该怎么解决？


以下是异常信息：type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Error allocating a servlet instance
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
java.lang.Thread.run(Unknown Source)
root cause java.lang.UnsupportedClassVersionError: Bad version number in .class file
java.lang.ClassLoader.defineClass1(Native Method)
java.lang.ClassLoader.defineClass(Unknown Source)
java.security.SecureClassLoader.defineClass(Unknown Source)
org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1853)
org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:875)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1330)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1209)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
java.lang.Thread.run(Unknown Source)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.26 logs.
以下是web.xml的内容：   <servlet>
<servlet-name>DisplayChart</servlet-name>
<servlet-class>org.jfree.chart.servlet.DisplayChart</servlet-class>
</servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>JFreechartServlet</servlet-name>
    <servlet-class>com.juanyuan.jfreechart.control.JFreechartServlet</servlet-class>
  </servlet><servlet-mapping>
<servlet-name>DisplayChart</servlet-name>
<url-pattern>/DisplayChart</url-pattern>
</servlet-mapping>
  <servlet-mapping>
    <servlet-name>JFreechartServlet</servlet-name>
    <url-pattern>/JFreechartServlet</url-pattern>
  </servlet-mapping>  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>一开始的时候，我是在1.4的编译器下实现的，
后来用6.0的时候就出现上面的异常。
大家帮忙看看。