我买了本书，照这做了个例子，上传到服务器无法显示，请大家帮我解决一下，谢谢！

  报错信息：
   HTTP Status 500 - 

--------------------------------------------------------------------------------

type Exception report

message 

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
sun.reflect.GeneratedMethodAccessor199.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:239)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:268)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:157)
java.security.AccessController.doPrivileged(Native Method)
com.ganchengnuo.trainingsystem.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:79)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:239)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:268)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:213)


root cause 

java.lang.NullPointerException
org.apache.jsp.aboutus_jsp._jspService(aboutus_jsp.java:187)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
sun.reflect.GeneratedMethodAccessor199.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:239)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:268)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:157)
java.security.AccessController.doPrivileged(Native Method)
com.ganchengnuo.trainingsystem.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:79)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:239)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:268)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:213)


note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.

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