log4j 還是 log4j 2 ?
- log4j 相容jdk6， 最新版本是1.2.17（不再更新）
- log4j2 不相容jdk7之前的版本, 最新版本是2.6.x (截止2016-06-15)
但是，log4j 2 採用了非同步寫檔案的機制，比log4j 提高了10倍以上的效能。

所以，對於還在用Java6的伺服器來說 請使用log4j。

新專案，儘量使用jdk 7 和 log4j 2

Java Web專案指定log4j.properties

<!-- 在 WebContent/WEB-INF/web.xml 中新增 -->
 

<listener>
    <listener-class>
            org.springframework.web.util.Log4jConfigListener
        </listener-class>
</listener>
<context-param>
    <param-name>log4jConfigLocation</param-name>
    <param-value>/WEB-INF/log4j.properties</param-value>
 

</context-param>
<context-param>
    <param-name>log4jRefreshInterval</param-name>
    <param-value>6000</param-value>
</context-param>

log4j

### set log levels ###
#設定rootLogger使用名為E和I的輸出設定
#第一個逗號前是根日誌等級
log4j.rootLogger = DEBUG , E , I

#windows下絕對路徑以tomcat安裝位置所在的碟符為準，
 

#如tomcat安裝位置在D盤，則d:\\wls\\apache\\applogs\\
mylog.home=/wls/apache/applogs/

## 管理引用的第三方 jar包的日誌輸出， OFF是關閉  
log4j.logger.org.springframework=OFF  
log4j.logger.org.apache.struts2=OFF  
log4j.logger.com.opensymphony.xwork2=OFF  
log4j.logger.com.ibatis=OFF  
log4j.logger.org.hibernate=OFF  
log4j.logger.java.sql.ResultSet=INFO  
log4j.logger.org.apache=INFO  
log4j.logger.java.sql.Connection=DEBUG  
log4j.logger.java.sql.Statement=DEBUG  
log4j.logger.java.sql.PreparedStatement=DEBUG

### Info Log File ###
log4j.appender.I = org.apache.log4j.RollingFileAppender
log4j.appender.I.File = ${mylog.home}info.log
log4j.appender.I.Append = true
# 防止在linux和windows上跑，中文編碼不一致，亂碼
log4j.appender.I.encoding=UTF-8
log4j.appender.I.Threshold = INFO
log4j.appender.I.MaxFileSize= 20000KB#DailyRollingFileAppender不支援
log4j.appender.I.MaxBackupIndex= 3   #DailyRollingFileAppender不支援
log4j.appender.I.layout = org.apache.log4j.PatternLayout
log4j.appender.I.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}[%5p] [ %c %4L] %m%n

###  Error Log file ###
log4j.appender.E = org.apache.log4j.RollingFileAppender
log4j.appender.E.File = ${pafa.log.home}error.log 
log4j.appender.E.Append = true
# 防止在linux和windows上跑，中文編碼不一致，亂碼
log4j.appender.E.encoding=UTF-8
log4j.appender.E.Threshold = ERROR 
log4j.appender.E.MaxFileSize= 20000KB
log4j.appender.E.MaxBackupIndex= 3
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %p ] [ %c %4L ] %m%n

巧用rootlevel和package日誌level禁止hibernate日誌輸出

#根使用FATAL（FATAL>ERROR>INFO）級別，這樣hibernate就不會輸出了
log4j.rootLogger=FATAL, A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n

#  com.foo.myapp 使用INFO級別輸出
log4j.logger.com.foo.myapp=INFO

log4j2

log4j 2 支援 properties 格式， xml 格式， json 格式的配置檔案。為了降低從 log4j 遷移到 log4j 2 的學習成本， 先使用 properties 格式。

src/log4j2.properties 內容如下，注意檔名要帶 “2”：

status = error
name = PropertiesConfig

property.filename = target/rolling/rollingtest.log

filters = threshold

filter.threshold.type = ThresholdFilter
filter.threshold.level = debug

#appenders = console, I, E
#不要輸出到console，要養成看日誌檔案的習慣
appenders =I, E

#appender.console.type = Console
#appender.console.name = STDOUT
#appender.console.target = SYSTEM_OUT
#appender.console.layout.type = PatternLayout
#appender.console.layout.pattern = %-d{yyyy-MM-dd HH:mm:ss} [ %p ] [ %c ] %m%n

appender.I.type = RollingFile
appender.I.name = InfoRollingFile
appender.I.fileName = /spider/logs/info.log
appender.I.filePattern = /spider/logs/info_%d{yyyy-MM-dd}_%i.log
appender.I.layout.type = PatternLayout
appender.I.layout.pattern = %-d{yyyy-MM-dd HH:mm:ss} [ %p ] [ %c ] %m%n
appender.I.policies.type = Policies
appender.I.policies.time.type = TimeBasedTriggeringPolicy
appender.I.policies.time.interval = 1
appender.I.policies.time.modulate = true
appender.I.policies.size.type = SizeBasedTriggeringPolicy
appender.I.policies.size.size=20M
appender.I.strategy.type = DefaultRolloverStrategy
appender.I.strategy.max = 100


appender.E.type = RollingFile
appender.E.name = ErrorRollingFile
appender.E.fileName = /spider/logs/error.log
appender.E.filePattern = /spider/logs/error_%d{yyyy-MM-dd}_i.log
appender.E.layout.type = PatternLayout
appender.E.layout.pattern = %-d{yyyy-MM-dd HH:mm:ss} [ %p ] [ %c ] %m%n
appender.E.policies.type = Policies
appender.E.policies.time.type = TimeBasedTriggeringPolicy
appender.E.policies.time.interval = 1
appender.E.policies.time.modulate = true
appender.E.policies.size.type = SizeBasedTriggeringPolicy
appender.E.policies.size.size=20M
appender.E.strategy.type = DefaultRolloverStrategy
appender.E.strategy.max = 100


rootLogger.level = info
#rootLogger.appenderRefs = stdout,I,E
rootLogger.appenderRefs =I,E
#rootLogger.appenderRef.stdout.ref = STDOUT
rootLogger.appenderRef.I.ref = InfoRollingFile
rootLogger.appenderRef.I.level = info
rootLogger.appenderRef.E.ref = ErrorRollingFile
rootLogger.appenderRef.E.level = error

log4j2的.xml的配置檔案, 支援指定哪些包輸出, .properties的配置檔案沒試過.

用Additivity禁止hibernate日誌輸出

Perhaps it is desired to eliminate all the TRACE output from everything except com.foo.Bar. Simply changing the log level would not accomplish the task. Instead, the solution is to add a new logger definition to the configuration:

It is possible to disable logging for certain parts of the application

如前文所述, log4j 允許你在不修改程式程式碼的前提下, 重新定義logging的行為. 禁止程式某些部分的日誌輸出是可行的.

src/log4j2.xml 內容如下，注意檔名中的“2”不可省略：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
        <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
    </Console>
    <File name="I" fileName="logs/info.log" bufferedIO="false"
        advertise="true">
        <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
    </File>
    <File name="E" fileName="logs/error.log" bufferedIO="false"
        advertise="true">
        <ThresholdFilter level="error" onMatch="ACCEPT" onMismatch="DENY"/>
        <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
    </File>
</Appenders>

  <Loggers>
    <!--制定輸出com包中的logger-->
    <Logger name="com" level="debug"> 
      <AppenderRef ref="Console"/>
      <AppenderRef ref="I"/>
      <AppenderRef ref="E"/>
    </Logger>

    <!--忽略hibernate等第三方包的日誌-->
    <Root level="OFF">
    </Root>

  </Loggers>
</Configuration>

log4j 2 非同步配置

關鍵配置：

<appender name="xxx" class="org.apache.log4j.AsyncAppender"> 
<!--快取大小影響效能 256 時最佳-->
<param name="BufferSize" value="512"/>