jsp读取文件在weblogic下出错

我写了一个读取服务器文件的jsp，在tomgcat下测试通过，不过在weblogic上出错，错误消息如下：
Error 500--Internal Server Error
java.lang.NullPointerException
at jsp_servlet.__readlog._jspService(Ljavax/servlet/http/HttpServletRequest;Ljavax/servlet/http/HttpServletResponse;)V(__readlog.java:133)
at weblogic.servlet.jsp.JspBase.service(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;)V(JspBase.java:33)
at weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run()Ljava/lang/Object;(ServletStubImpl.java:1072)
at weblogic.servlet.internal.ServletStubImpl.invokeServlet(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;Lweblogic/servlet/internal/FilterChainImpl;)V(ServletStubImpl.java:465)
at weblogic.servlet.internal.ServletStubImpl.invokeServlet(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;Lweblogic/servlet/internal/FilterChainImpl;)V(ServletStubImpl.java:526)
at weblogic.servlet.internal.ServletStubImpl.invokeServlet(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;)V(ServletStubImpl.java:348)
at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run()Ljava/lang/Object;(WebAppServletContext.java:6981)
at weblogic.security.acl.internal.AuthenticatedSubject.doAs(Lweblogic/security/subject/AbstractSubject;Ljava/security/PrivilegedAction;)Ljava/lang/Object;(AuthenticatedSubject.java:321)
at weblogic.security.service.Sec