java - 为什么我会收到这个奇怪的 log4j 异常？

Question

我有一个已经运行了几个月的代码库，今天我部署了一个更新到一个客户站点，我开始收到以下异常:

Exception in thread "Thread-75" Exception in thread "Thread-66" java.lang.NullPointerException at org.apache.log4j.spi.LocationInfo.(LocationInfo.java:112) at org.apache.log4j.spi.LoggingEvent.getLocationInformation(LoggingEvent.java:247) at org.apache.log4j.helpers.PatternParser$LocationPatternConverter.convert(PatternParser.java:483) at org.apache.log4j.helpers.PatternConverter.format(PatternConverter.java:65) at org.apache.log4j.PatternLayout.format(PatternLayout.java:502) at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:302) at org.apache.log4j.RollingFileAppender.subAppend(RollingFileAppender.java:263) at org.apache.log4j.WriterAppender.append(WriterAppender.java:160) at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251) at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:66) at org.apache.log4j.Category.callAppenders(Category.java:206) at org.apache.log4j.Category.forcedLog(Category.java:391) at org.apache.log4j.Category.debug(Category.java:260)

启动它的代码是一个 log.debug() 语句，我不知道为什么会这样。它在我的机器上也能正常工作，但在客户站点上却失败了。

这是日志配置的匿名版本:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <appender name="stdout" class="org.apache.log4j.ConsoleAppender"> 
    <param name="Threshold" value="ERROR"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <!-- Print the date in ISO 8601 format -->
      <param name="ConversionPattern" value="[%d{dd-MM-yyyy HH:mm:ss.SS}][line:%3L] [%5p] [%F %M()] - %m%n"/> 
    </layout> 
  </appender> 
  <appender name="x_trace" class="org.apache.log4j.RollingFileAppender"> 
    <param name="File" value="C:/apache-tomcat-5.5.17/logs/x_trace.log"/>
    <param name="MaxFileSize" value="100MB" />
    <param name="MaxBackupIndex" value="10" />
    <param name="Append" value="true"/>
    <param name="Threshold" value="ALL"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="[%d{dd-MM-yyyy HH:mm:ss.SS}][line:%3L]%5p [%t] ( %F %M()) - %m%n"/> 
    </layout> 
  </appender>  
  <appender name="y_trace" class="org.apache.log4j.RollingFileAppender"> 
    <param name="File" value="C:/apache-tomcat-5.5.17/logs/y_trace.log"/>
    <param name="MaxFileSize" value="100MB" />
    <param name="MaxBackupIndex" value="10" />
    <param name="Append" value="true"/>
    <param name="Threshold" value="ALL"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="[%d{dd-MM-yyyy HH:mm:ss.SS}][line:%3L]%5p [%t] ( %F %M()) - %m%n"/> 
    </layout> 
  </appender>  
  <appender name="application" class="org.apache.log4j.RollingFileAppender"> 
    <param name="File" value="C:/apache-tomcat-5.5.17/logs/application.log"/>
    <param name="MaxFileSize" value="100MB" />
    <param name="MaxBackupIndex" value="20" />
    <param name="Append" value="true"/>
    <param name="Threshold" value="ALL"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="[%d{dd-MM-yyyy HH:mm:ss.SS}][line:%3L]%5p [%t] ( %F %M()) - %m%n"/> 
    </layout> 
  </appender> 
  <!-- failureLogger Logs SQL queries that were not written to the database so they can be rolled in -->
  <appender name="failureLogger" class="org.apache.log4j.DailyRollingFileAppender"> 
    <param name="File" value="C:/apache-tomcat-5.5.17/logs/failures.log"/>
    <param name="Append" value="true"/>
    <param name="Threshold" value="ALL"/>
    <param name="DatePattern" value="'.'yyyy-MM-dd"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="%m%n"/> 
    </layout> 
  </appender> 
  <logger name="nanoxml" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger>   
  <logger name="uk.co.companyName.application" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger>   
  <logger name="uk.co.companyName.application.applicationContainer" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger> 
  <logger name="uk.co.companyName.application.addressbook.AddressBook" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger>   
   <logger name="uk.co.companyName.application.component1.Component1" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger>   
  <logger name="uk.co.companyName.application.component2.Component2" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger>  
  <logger name="uk.co.companyName.application.web.filters" additivity="false">
    <level value="error"/>  
    <appender-ref ref="application"/>
  </logger>  
  <logger name="uk.co.companyName.application.web" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger>  
  <logger name="uk.co.companyName.application.util.SettingsHandler" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger> 
  <logger name="uk.co.companyName.application.util" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>
  </logger> 
  <logger name="org.apache.axis.enterprise" additivity="false">
    <level value="FATAL"/>  
    <appender-ref ref="application"/>
  </logger>  
  <logger name="com.vendor.api1" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="x_trace"/>
  </logger>
  <logger name="com.vendor.api2" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="y_trace"/>
  </logger>
  <logger name="com.vendor.lib1" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="y_trace"/>
  </logger>
  <logger name="ch.ecma" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="y_trace"/>
  </logger>
  <logger name="uk.co.companyName.vendor.middlewareAPI" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger>
  <logger name="uk.co.companyName.vendor2.workStationAPI" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger>   
  <logger name="uk.co.companyName.CustomerLib1" additivity="false">
    <level value="debug"/>  
    <appender-ref ref="application"/>   
  </logger>   
  <logger name="FaileStatementLogger" additivity="false">
    <level value="debug"/>
    <appender-ref ref="failureLogger"/>
  </logger>
  <root>  
    <priority value="DEBUG" />
    <!-- <appender-ref ref="stdout" /> -->
  </root>
</log4j:configuration>

Answer 1

基于code for 1.2.15 , 看起来 private static StringWriter 是 null，这可能表示可用​​内存不足。不能 100% 确定在何种情况下类(class)会以这种情况结束。

具体来说，代码如下所示

56    private static StringWriter sw = new StringWriter();
57    private static PrintWriter pw = new PrintWriter(sw);

112    synchronized(sw) {
113        t.printStackTrace(pw);
114        s = sw.toString();
115        sw.getBuffer().setLength(0);
116    }

您将获得同步调用的 NPE，它位于静态成员上。