Java中出现的空指针异常

org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet jsp threw exception java.lang.NullPointerException at org.apache.jsp.main_jsp._jspService(main_jsp.java:118) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at sun.reflect.GeneratedMethodAccessor33.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAsPrivileged(Unknown Source) at org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276) at org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:283) at org.apache.catalina.core.ApplicationFilterChain.access$000(ApplicationFilterChain.java:56) at org.apache.catalina.core.ApplicationFilterChain$1.run(ApplicationFilterChain.java:189) at java.security.AccessController.doPrivileged(Native Method) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:185) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286) at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190) at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283) at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767) at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697) at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690) at java.lang.Thread.run(Unknown Source)

出现空指针一般看第一个出错的位置

此列中出错位置在main_jsp.java:118 在118行去看看 它的值是否为空

具体原因只有这些信息时不够的 你需要去程序里面看看，具体问题具体分析！！

仔细找找错，空指针是常见的异常，一般都是你程序中如果有个对象有可能为null，而你又调用了它的方法，就会出现！如： String st = null; st.toString();//这样就会有空指针，你仔细分析程序，不会很难找，像这样的错误你应该自己学会排除！这是学java最基本的！好自为之