Node.js的日志默认打印到控制台，为数据收集和问题调查带来不便。通过log4js可以实现把日志打印到文件、自定义日志格式等功能，便于数据收集和整理。

1. [backcolor=transparent]var[backcolor=transparent] log4js [backcolor=transparent]=[backcolor=transparent] [backcolor=transparent]require[backcolor=transparent]([backcolor=transparent]'log4js'[backcolor=transparent]);

2. [backcolor=transparent]log4js[backcolor=transparent].[backcolor=transparent]configure[backcolor=transparent]({

3. [backcolor=transparent]  appenders[backcolor=transparent]:[backcolor=transparent] [backcolor=transparent][

4. [backcolor=transparent]    [backcolor=transparent]{[backcolor=transparent]  

5. [backcolor=transparent]      type[backcolor=transparent]:[backcolor=transparent] [backcolor=transparent]'file'[backcolor=transparent],[backcolor=transparent] [backcolor=transparent]//文件输出

6. [backcolor=transparent]      filename[backcolor=transparent]:[backcolor=transparent] [backcolor=transparent]'logs/access.log'[backcolor=transparent],[backcolor=transparent]

7. [backcolor=transparent]      maxLogSize[backcolor=transparent]:[backcolor=transparent] [backcolor=transparent]1024[backcolor=transparent],

8. [backcolor=transparent]      backups[backcolor=transparent]:[backcolor=transparent]3[backcolor=transparent],

9. [backcolor=transparent]      category[backcolor=transparent]:[backcolor=transparent] [backcolor=transparent]'normal'[backcolor=transparent]

10. [backcolor=transparent]    [backcolor=transparent]}[backcolor=transparent]  

11. [backcolor=transparent]  [backcolor=transparent]]

12. [backcolor=transparent]});

13. [backcolor=transparent]var[backcolor=transparent] logger [backcolor=transparent]=[backcolor=transparent] log4js[backcolor=transparent].[backcolor=transparent]getLogger[backcolor=transparent]([backcolor=transparent]'normal'[backcolor=transparent]);

14. [backcolor=transparent]logger[backcolor=transparent].[backcolor=transparent]setLevel[backcolor=transparent]([backcolor=transparent]'INFO'[backcolor=transparent]);

15. [backcolor=transparent]logger[backcolor=transparent].[backcolor=transparent]info[backcolor=transparent]([backcolor=transparent]"this is a info msg"[backcolor=transparent]);

16. [backcolor=transparent]logger[backcolor=transparent].[backcolor=transparent]error[backcolor=transparent]([backcolor=transparent]"this is a err msg"[backcolor=transparent]);

 
 
日志格式 
 
 
通过log4js实现日志数据存储为文本文件格式后，日志在文件中显示为以下格式：

1. [backcolor=transparent][[backcolor=transparent]2016[backcolor=transparent]-[backcolor=transparent]02[backcolor=transparent]-[backcolor=transparent]24[backcolor=transparent] [backcolor=transparent]17[backcolor=transparent]:[backcolor=transparent]42[backcolor=transparent]:[backcolor=transparent]38.946[backcolor=transparent]][backcolor=transparent] [backcolor=transparent][[backcolor=transparent]INFO[backcolor=transparent]][backcolor=transparent] normal [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]this[backcolor=transparent] [backcolor=transparent]is[backcolor=transparent] a info msg

2. [backcolor=transparent][[backcolor=transparent]2016[backcolor=transparent]-[backcolor=transparent]02[backcolor=transparent]-[backcolor=transparent]24[backcolor=transparent] [backcolor=transparent]17[backcolor=transparent]:[backcolor=transparent]42[backcolor=transparent]:[backcolor=transparent]38.951[backcolor=transparent]][backcolor=transparent] [backcolor=transparent][[backcolor=transparent]ERROR[backcolor=transparent]][backcolor=transparent] normal [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]this[backcolor=transparent] [backcolor=transparent]is[backcolor=transparent] a err msg

 
log4js分为6个输出级别，从低到高分别为trace、debug、info、warn、error、fatal。 
 
通过Logtail收集Node.js日志 
 
 
配置Logtail收集Python日志的详细操作步骤请参考快速入门和apache日志，根据您的网络部署和实际情况选择对应配置。 
在生成正则式的部分，由于自动生成的正则式只参考了日志样例，无法覆盖所有的日志情况，所以需要用户在自动生成之后做一些微调。您可以参考以下Node.js日志示例，为您的日志撰写正确、全面的正则表达式。 
[backcolor=transparent]常见的Node.js日志及其正则表达式：

·  
Node.js日志示例1 
日志示例：

[backcolor=transparent][[backcolor=transparent]2016[backcolor=transparent]-[backcolor=transparent]02[backcolor=transparent]-[backcolor=transparent]24[backcolor=transparent] [backcolor=transparent]17[backcolor=transparent]:[backcolor=transparent]42[backcolor=transparent]:[backcolor=transparent]38.946[backcolor=transparent]][backcolor=transparent] [backcolor=transparent][[backcolor=transparent]INFO[backcolor=transparent]][backcolor=transparent] normal [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]this[backcolor=transparent][backcolor=transparent]is[backcolor=transparent] a info msg

·  
正则表达式：

[backcolor=transparent]\[[backcolor=transparent]([^]]+)][backcolor=transparent]\s\[[backcolor=transparent]([^[backcolor=transparent]\][backcolor=transparent]]+)][backcolor=transparent]\s[backcolor=transparent]([backcolor=transparent]\w[backcolor=transparent]+)[backcolor=transparent]\s[backcolor=transparent]-(.*)

·  
提取字段： 
time、level、loggerName和message。

 
Node.js日志示例2：

·  
日志示例：

[backcolor=transparent][[backcolor=transparent]2016[backcolor=transparent]-[backcolor=transparent]01[backcolor=transparent]-[backcolor=transparent]31[backcolor=transparent] [backcolor=transparent]12[backcolor=transparent]:[backcolor=transparent]02[backcolor=transparent]:[backcolor=transparent]25.844[backcolor=transparent]][backcolor=transparent] [backcolor=transparent][[backcolor=transparent]INFO[backcolor=transparent]][backcolor=transparent] access [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]42.120[backcolor=transparent].[backcolor=transparent]73.203[backcolor=transparent] [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]"GET /user/projects/ali_sls_log?ignoreError=true HTTP/1.1"[backcolor=transparent] [backcolor=transparent]304[backcolor=transparent] [backcolor=transparent]-[backcolor=transparent] [backcolor=transparent]"//

1. [backcolor=transparent]aliyun.com/"[backcolor=transparent] [backcolor=transparent]"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.97 Safari/537.36"

·  
正则表达式：

[backcolor=transparent]\[[backcolor=transparent]([^]]+)][backcolor=transparent]\s\[[backcolor=transparent]([backcolor=transparent]\w[backcolor=transparent]+)][backcolor=transparent]\s[backcolor=transparent]([backcolor=transparent]\w[backcolor=transparent]+)[backcolor=transparent]\s[backcolor=transparent]-[backcolor=transparent]\s[backcolor=transparent]([backcolor=transparent]\S[backcolor=transparent]+)[backcolor=transparent]\s[backcolor=transparent]-[backcolor=transparent]\s[backcolor=transparent]-[backcolor=transparent]\s[backcolor=transparent]"([^"[backcolor=transparent]]+)[backcolor=transparent]"\s(\d+)[^"[backcolor=transparent]]+([backcolor=transparent]"[^"[backcolor=transparent]]+)[backcolor=transparent]"\s"[backcolor=transparent]([^[backcolor=transparent]"]+).*

·  
提取字段： 
time、level、loggerName、ip、 request、status、referer和user_agent。

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