Java - 如何仅读取输入流的某些部分

Question

我有一个要求，我需要解析输入文件并仅读取文件的某些部分。我有一个日志文件，它具有不同的级别，例如信息警告和错误。现在我只需要读取包含完整错误堆栈跟踪的部分。我怎样才能使用java来实现这一点？

例如：

INFO  | 2011-04-13 17:59:22,810 | Calling Feedback from 127.0.0.1 
INFO  | 2011-04-13 17:59:24,920 | Successfully called Feedback from 127.0.0.1
INFO  | 2011-04-13 17:59:31,561 | FeedBackList

ERROR | 2011-04-13 19:00:41,640 |  
java.util.concurrent.TimeoutException
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:228)
    at java.util.concurrent.FutureTask.get(FutureTask.java:91)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
    at org.springframework.orm.hibernate3.HibernateInterceptor.invoke(HibernateInterceptor.java:111)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
    at $Proxy309.getConsumerProfileData(Unknown Source)
    at com.scea.usps.model.service.impl.AccountSettingsServiceImpl.getUserProfile(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
    at org.springframework.orm.hibernate3.HibernateInterceptor.invoke(HibernateInterceptor.java:111)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
    at $Proxy284.getUserProfile(Unknown Source)
    at com.scea.usps.model.common.PsninfoUtility.getTop3Generes(Unknown Source)
    at com.scea.usps.model.common.PsninfoUtility.updatePsnInfoDetail(Unknown Source)
    at com.scea.platform.framework.api.PsnInfoThread.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:619)

INFO  | 2011-04-13 17:59:22,810 | Calling Feedback from 127.0.0.1 
INFO  | 2011-04-13 17:59:24,920 | Successfully called Feedback from 127.0.0.1
INFO  | 2011-04-13 17:59:31,561 | FeedBackList

在上面的日志中，我需要提取（读取）从 ERROR 开始直到堆栈跟踪结束的所有行。请分享您对此的想法。谢谢。

Answer 1

BufferedReader in = new BufferedReader(new FileReader("logfile.log"));
  String line = in.readLine();
  StringBuffer buf = null;
  while (line != null) {
    if(line.startsWith("ERROR")){
       buf = new StringBuffer();
       buf.append(line).append("\n");
       while(line != null && !line.trim().equals("")){
          line = in.readLine();
          buf.append(line).append("\n");
       }
       //Now buf has your error an do whatever you want to do with it
       //then delete
       buf = null;
    }
    line = in.readLine();
  }

Answer 2

如果您的目标是查看应用程序日志中的错误，那么像 Chainsaw 这样的工具可能是更好的解决方案。

Answer 3

如果您使用 LogFilePatternReceiver，Chainsaw 确实具有此内置功能。您可以定义一个filterExpression，并且只有与该filterExpression匹配的事件才会被处理。

仅包含堆栈跟踪的示例过滤器表达式为：

存在异常

您必须提供日志文件的格式。有关详细信息，请参阅 JavaDoc：

http: //logging.apache.org/log4j/companions/receivers/apidocs/org/apache/log4j/varia/LogFilePatternReceiver.html

Answer 4

• 打开文件
• 读取，直到遇到错误
• 读取行，并处理行，直到遇到堆栈跟踪后的空行。

冲洗，重复。

Answer 5

try {
      BufferedReader in
          = new BufferedReader(new FileReader("logfile.log"));
      String line = in.readLine();
      while (!line.startsWith("ERROR")) {
        line = in.readLine();
        if(line==null){
          //throw exception here, ERROR not found in entire log file
        }
      }
      //HERE line will be your error line
      while (line!=null) {
        line = in.readLine();
        //do something with line
      }
      //here you have reached the end of the file
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }