log4j2 与 log4j使用时的几点小区别 - log4j2上手说明

虽然log4j2 目前还是beta版，不过OneCoder已经忍不住要尝试一下。跟使用log4j 比起来，上手上主要的区别有。
1、依赖的jar包。使用slf4j+log4j2 时，依赖的jar包如下：(gradle配置，Maven对照修改即可)

dependencies{
compile(
"org.apache.logging.log4j:log4j-api:$log4j_version",
"org.apache.logging.log4j:log4j-core:$log4j_version",
"org.apache.logging.log4j:log4j-slf4j-impl:$log4j_version"
)

}

其中，log4j_version=2.0-beta9

2、默认配置文件名字
默认搜索的配置文件名字变为log4j2或log4j-test开头的配置文件，这个变化，让OneCoder吃了些苦头。没注意观察，还自以为配置文件还是log4j.xml，结果怎么都不管用。后来仔细阅读官方文档才发现问题。log4j2中，支持json和xml两个格式的配置文件，配置文件的搜索顺序为：

  1. Log4j will inspect the "log4j.configurationFile" system property and, if set, will attempt to load the configuration using the ConfigurationFactory that matches the file extension.
  2. If no system property is set the JSON ConfigurationFactory will look for log4j2-test.json or log4j2-test.jsn in the classpath.
  3. If no such file is found the XML ConfigurationFactory will look for log4j2-test.xml in the classpath.
  4. If a test file cannot be located the JSON ConfigurationFactory will look for log4j2.json or log4j2.jsn on the classpath.
  5. If a JSON file cannot be located the XML ConfigurationFactory will try to locate log4j2.xml on the classpath.
  6. If no configuration file could be located the DefaultConfiguration will be used. This will cause logging output to go to the console.

环境变量log4j.configurationFile指定的文件->log4j2-test.json/log4j2-test.jsn -> log4j2-test.xml -> log4j2.json/log4j2.jsn -> log4j2.xml - > 默认配置DefaultConfiguration

3、配置文件格式

配置文件样例，跟1比起来有所简化。

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
     <Appenders>
          <Console name="Console" target="SYSTEM_OUT">
               <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5level %l - %msg%n" />
          </Console>
     </Appenders>
     <Loggers>
          <Root level="debug">
               <AppenderRef ref="Console" />
          </Root>
     </Loggers>
</Configuration>

其他的变化和优势，您可以在使用中慢慢体会了。