Java - 如何只讀取輸入流的某些部分

Question

我有一個需求，我需要解析輸入文件並只讀取文件的某些部分。我有一個日誌文件，它有不同的級別，如信息警告和錯誤。現在我只需要讀取包含完整錯誤堆棧跟蹤的部分。我怎樣才能實現這一點使用Java。

例：

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 

在上述日誌I需要提取（讀出）從ERROR開始直到堆棧跟蹤結束的所有行。請在此分享您的想法。謝謝。

Answer 1

• 打開文件
• 看，直到你擊中錯誤
• 讀取和處理線的線條，直到你遇到堆棧跟蹤後的空白行。

沖洗，重複。

Answer 2

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(); 
    } 
    } 

Answer 3

如果你的目標是看你的應用程序的錯誤日誌，然後像Chainsaw的工具可能是一個更好的解決方案。

Answer 4

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 5

如果您使用LogFilePatternReceiver，電鋸確實具有此內置功能。你可以定義一個filterExpression，並且只有匹配該filterexpression的事件纔會被處理。

一個例子篩選表達式，將只包括堆棧跟蹤是：

存在例外

你必須提供你的日誌文件的格式。查看javadoc瞭解更多信息：

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