node.js学习笔记（23） log4js

在前面的笔记里讲过express-genrator创建的express项目使用morgan日志，将morgan作为应用级中间件，express项目就会自动记录http访问日志。

Morgan默认了5中日志的格式，也可以让用户自定义日志格式，是一个简单使用的日志中间件。

但是，我用java编程多年，非常清楚log4j的强大与好用。因此，仅仅log4js这个名字就已经让我先入为主了，尽管morgan也是一个不错的日志中间件。

Log4js相比morgan，更加强大，更加贴近java程序员的习惯。

Section 1

让我们从一个简单是例子来开始log4js的体验：

mkdir log4js-examples
cd log4js-examples
npm init
npm install log4js

var log4js = require('log4js');
var logger = log4js.getLogger();
logger.debug("Some debug messages");

lee@mypc ~/works/nodejs/study23/log4js-examples $ node log4js-minimal.js 
[2016-01-19 19:07:08.258] [DEBUG] [default] - Some debug messages

Section 2

再来一个输出到文件，log4js-file.js:

var log4js = require('log4js');
//console log is loaded by default, so you won't normally need to do this
//log4js.loadAppender('console');
log4js.loadAppender('file');
//log4js.addAppender(log4js.appenders.console());
log4js.addAppender(log4js.appenders.file('logs/cheese.log'), 'cheese');

var logger = log4js.getLogger('cheese');
logger.setLevel('ERROR');

logger.trace('Entering cheese testing');
logger.debug('Got cheese.');
logger.info('Cheese is Gouda.');
logger.warn('Cheese is quite smelly.');
logger.error('Cheese is too ripe!');
logger.fatal('Cheese was breeding ground for listeria.');

运行：

lee@mypc ~/works/nodejs/study23/log4js-examples $ node log4js-file.js 
[2016-01-19 19:11:16.447] [ERROR] cheese - Cheese is too ripe!
[2016-01-19 19:11:16.452] [FATAL] cheese - Cheese was breeding ground for listeria.
lee@mypc ~/works/nodejs/study23/log4js-examples $ ls logs
cheese.log
lee@mypc ~/works/nodejs/study23/log4js-examples $ cat logs/cheese.log 
[2016-01-19 14:02:40.929] [ERROR] cheese - Cheese is too ripe!
[2016-01-19 14:02:40.933] [FATAL] cheese - Cheese was breeding ground for listeria.

Section 3

log4js-file.js也可以这样配置，效果是一样的。

log4js-configure.js:

var log4js = require('log4js');
log4js.configure({
    appenders: [
        { type: 'console' },
        { type: 'file', filename: 'logs/cheese-configure.log', category: 'cheese' }
    ]
});

var logger = log4js.getLogger('cheese');
logger.setLevel('ERROR');

logger.trace('Entering cheese testing');
logger.debug('Got cheese.');
logger.info('Cheese is Gouda.');
logger.warn('Cheese is quite smelly.');
logger.error('Cheese is too ripe!');
logger.fatal('Cheese was breeding ground for listeria.');

我们在javaEE中使用log4j的时候，总是习惯配置log4j.properties，有没有？！

Log4js也可以从配置文件来读取配置。

configfile.json:

{
  "appenders": [
    { "type": "console" },
    { "type": "file", "filename": "logs/cheese-configfile.log", "category": "cheese" }
  ]
}

log4js-configfile.js:

var log4js = require('log4js');
log4js.configure('configfile.json');

var logger = log4js.getLogger('cheese');
logger.setLevel('ERROR');

logger.trace('Entering cheese testing');
logger.debug('Got cheese.');
logger.info('Cheese is Gouda.');
logger.warn('Cheese is quite smelly.');
logger.error('Cheese is too ripe!');
logger.fatal('Cheese was breeding ground for listeria.');

log4js完全想morgan一样当express的中间件用。

来试一下

创建一个项目log-log4js:

express log-log4js
cd log-log4js
#install node-modules
npm install
#install log4js
npm install log4js
#create a directory for save log files
mkdir logs

可以这样修改app.js:

...
//var logger = require('morgan');
var log4js = require('log4js');
...
//app.use(logger('dev'));
log4js.configure({
  appenders: [
    { type: 'console' }, //控制台输出
    {
      type: 'file', //文件输出
      filename: 'logs/access.log',
      maxLogSize: 1024,
      backups:3,
      category: 'normal'
    }
  ]
});
var logger = log4js.getLogger('normal');
logger.setLevel(log4js.levels.INFO);
app.use(log4js.connectLogger(logger, {level:log4js.levels.INFO}));
...

npm start

curl http://localhost:3000/
curl http://localhost:3000/users

lee@mypc ~/works/nodejs/study23/log-log4js $ ls logs
access.log
lee@mypc ~/works/nodejs/study23/log-log4js $ cat logs/access.log 
[2016-01-22 20:40:54.977] [INFO] normal - ::ffff:127.0.0.1 - - "GET / HTTP/1.1" 200 170 "" "curl/7.35.0"
[2016-01-22 20:41:03.245] [INFO] normal - ::ffff:127.0.0.1 - - "GET /users HTTP/1.1" 200 23 "" "curl/7.35.0"
[2016-01-22 20:41:05.817] [INFO] normal - ::ffff:127.0.0.1 - - "GET / HTTP/1.1" 200 170 "" "curl/7.35.0"
[2016-01-22 20:41:07.422] [INFO] normal - ::ffff:127.0.0.1 - - "GET /users HTTP/1.1" 200 23 "" "curl/7.35.0"

Section 6

看到这儿，有没有发现section2中的代码输出了很多日志信息，而在日志文件中却只有两行。

Log4js一定有比morgan更强大的地方，否则它就不配叫log4js。

Log4js的输出级别有6个，从低到高分别是 trace, debug, info, warn, error, fatal。

在section2的实例中，设置了log的输出级别是error，所以低于error级别的trace,debug,info和warn都没有输出。

设置输出级别的好处尤其体现在测试环境和生产环境，测试环境中跟踪测试，往往需要非常详细的debug信息，而在生产环境中运行稳定版本则不需要过多的日志信息，只需要必要的warn,error或fetal。