第一步：定位出现异常的行， java 的异常，通常包含 Exception 字样
grep -n "Exception" catalina.out
该指令的 -n 参数会打印符合条件的行的行号，示例输出如下：
[itims@localhost logs]$ grep -n "Exception" catalina.out
33642:java.lang.NullPointerException
33910:java.lang.NullPointerException
34213:java.lang.NullPointerException
34523:java.lang.NullPointerException
34597:java.lang.NullPointerException
第二步 ： 截取 Exception 所在行的前后各 10 行。
比如我们想关注 33910 行的 NullPointerException ， 可以用如下指令 ：
head -33920 catalina.out | tail -20
该指令会得到如下输出 ：
[itims@localhost logs]$ head -33920 catalina.out | tail -20
Asia/Shanghai
CN
/usr/local/jdk1.5.0_12/jre
Thu Sep 17 11:13:00 GMT+08:00 2009
17 Sep 2009 03:13:00 GMT
2009-9-17 11:13:00
2009-09-17 11:13:00
java.util.GregorianCalendar[time=1253157180432,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="GMT+08:00",offset=28800000,dstSavings=0,useDaylight=false,transitions=0,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2009,MONTH=8,WEEK_OF_YEAR=38,WEEK_OF_MONTH=3,DAY_OF_MONTH=17,DAY_OF_YEAR=260,DAY_OF_WEEK=5,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=11,HOUR_OF_DAY=11,MINUTE=13,SECOND=0,MILLISECOND=432,ZONE_OFFSET=28800000,DST_OFFSET=0]
null
java.lang.NullPointerException
at itims.share.db.GlobalTransaction.rollback(GlobalTransaction.java:125)
at itims.web.frmwk.NetElementService.deleteNetelement(NetElementService.java:292)
at org.apache.jsp.frmwk.deletene_jsp._jspService(deletene_jsp.java:77)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)