log4j在java开发中的使用之详解

我们在实际开发中需要使用控制台打印出每一步的请求的sql语句，方便调试，同时也需要部署到服务器之后，需要每天生成log文件，这样若是有问题就可以直接去查看，对于一些不常见的问题不用费尽心思去重现。首先需要了解Commons-logging，log4j，slf4j的区别

以上三个都是针对日志的，但是有什么区别呢？

Commons-logging : apache最早提供的日志的门面接口。避免和具体的日志方案直接耦合。类似于JDBC 的api 接口，具体的的JDBC driver 实现由各数据库提供商实现。通过统一接口解耦，不过其内部也实现了一些简单日志方案。

Log4j : 经典的一种日志解决方案。内部把日志系统抽象封装成Logger 、appender 、pattern 等实现。我们可以通过配置文件轻松的实现日志系统的管理和多样化配置。

Slf4j : 全称为Simple Logging Facade for JAVA：java简单日志门面。 是对不同日志框架提供的一个门面封装。可以在部署的时候不修改任何配置即可接入一种日志实现方案。和commons-loging 应该有一样的初衷。个人感觉设从计上更好一些，没有commons 那么多潜规则。同时有两个额外特点：

1. 能支持多个参数，并通过{} 占位符进行替换，避免老写logger.isXXXEnabled 这种无奈的判断，带来性能提升见：http://www.slf4j.org/faq.html#logging_performance 。

 2.OSGI 机制更好兼容支持

总的来说就是slf4j是日志的接口（只定义了一些方法而没有去实现），和commons-logging一样。而log4j是具体的实现（即怎么来打印日志等），和logback是一样的。slf4j与commons-logging只是一个日志门面，实际还是要依赖真正的日志库log4j，属于log4j最强大，不需要依赖其他包

Log4j支持两种配置文件格式，一种是XML（标准通用标记语言下的一个应用）格式的文件，一种是Java特性文件log4j.properties（键=值）。

第一种：

slf4j+log4j组合使用模式：

1.log4j-1.2.14.jar

2.slf4j-api-1.6.1.jar

3.slf4j-jdk14-1.6.1.jar

4. log4j.properties(也可以是 log4j.xml)

import  org.slf4j.Logger;
import  org.slf4j.LoggerFactory;
Logger logger = LoggerFactory.getLogger(xx.class);

第二种： 

 JCL+Log4J组合使用模式（即commons-logging+log4j）：

1. commons-logging-1.1.jar
2. log4j-1.2.15.jar
3. log4j.properties(也可以是 log4j.xml)

import org.apache.commons.logging.Log; 
import org.apache.commons.logging.LogFactory;
private static Log log = LogFactory.getLog(xx.class);

 第三种：

log4j：

import org.apache.log4j.Logger;
Logger logger= Logger.getLogger(xx.class);

1.首先是struts2+myBatis的组合，我们采用第三种的方式来实现，4个jar包均有，log4j的properties

/**
 * 此句为将等级为INFO的日志信息输出到stdout和R这两个目的地，stdout和R的定义在下面的代码，可以任意起名。等级可分为OFF、FATAL、ERROR、WARN、INFO、DEBUG、ALL，如果配置OFF则不打出任何信息，如果配置为INFO这样只显示INFO, WARN, ERROR的log信息，而DEBUG信息不会被显示.
 */
log4j.rootCategory=info,STDOUT,R
/**
* 此句为定义名为stdout的输出端是哪种类型，可以是
org.apache.log4j.ConsoleAppender（控制台），
org.apache.log4j.FileAppender（文件），
org.apache.log4j.DailyRollingFileAppender（每天产生一个日志文件），
org.apache.log4j.RollingFileAppender（文件大小到达指定尺寸的时候产生一个新的文件）
org.apache.log4j.WriterAppender（将日志信息以流格式发送到任意指定的地方）
 */
log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender
/**
* 此句为定义名为stdout的输出端的layout是哪种类型，可以是
org.apache.log4j.HTMLLayout（以HTML表格形式布局），
org.apache.log4j.PatternLayout（可以灵活地指定布局模式），
org.apache.log4j.SimpleLayout（包含日志信息的级别和信息字符串），
org.apache.log4j.TTCCLayout（包含日志产生的时间、线程、类别等等信息）
*/
log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout
/**
* 如果使用pattern布局就要指定的打印信息的具体格式ConversionPattern，打印参数如下：
%m 输出代码中指定的消息
%p 输出优先级，即DEBUG，INFO，WARN，ERROR，FATAL
%r 输出自应用启动到输出该log信息耗费的毫秒数
%c 输出所属的类目，通常就是所在类的全名
%t 输出产生该日志事件的线程名
%n 输出一个回车换行符，Windows平台为“rn”，Unix平台为“n”
%d 输出日志时间点的日期或时间，默认格式为ISO8601，也可以在其后指定格式，比如：%d{yyyy MMM dd HH:mm:ss,SSS}，输出类似：2002年10月18日 22：10：28，921
%l 输出日志事件的发生位置，包括类目名、发生的线程，以及在代码中的行数。
*/
log4j.appender.STDOUT.layout.ConversionPattern=%d %-5p %c.%M:%L - %m%n
/**
* 定义名为R的输出端的类型为每天产生一个日志文件。
 */
log4j.appender.R=org.apache.log4j.DailyRollingFileAppender
/**
 * 定义名为R的输出端的文件名为${catalina.base}/logs/travel/travel.log可以自行修改。总之实在tomcat的log中即可
*/
log4j.appender.R.File=${catalina.base}/logs/travel/travel.log
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d %-5p %c.%M:%L - %m%n
/**
* mybaties的log配置，也就是能让mybaties的sql输出在控制台上
*/
log4j.logger.com.ibatis=debug
log4j.logger.com.ibatis.common.jdbc.SimpleDataSource=debug
log4j.logger.com.ibatis.common.jdbc.ScriptRunner=debug
log4j.logger.com.ibatis.sqlmap.engine.impl.SqlMapClientDelegate=debug

log4j.logger.java.sql.Connection=debug
log4j.logger.java.sql.Statement=debug
log4j.logger.java.sql.PreparedStatement=debug

 感兴趣的可以看看http://mybatis.github.io/mybatis-3/zh/logging.html这篇文章讲的很详细

2.struts2+hibernate的

使用的是xml的形式，但是要先引入log4j的dtd

<?xml version="1.0" encoding="UTF-8" ?>
<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<!-- Authors: Chris Taylor, Ceki Gulcu. -->

<!-- Version: 1.2 -->

<!-- A configuration element consists of optional renderer
elements,appender elements, categories and an optional root
element. -->

<!ELEMENT log4j:configuration (renderer*, appender*,plugin*, (category|logger)*,root?,
                               (categoryFactory|loggerFactory)?)>

<!-- The "threshold" attribute takes a level value below which -->
<!-- all logging statements are disabled. -->

<!-- Setting the "debug" enable the printing of internal log4j logging   -->
<!-- statements.                                                         -->

<!-- By default, debug attribute is "null", meaning that we not do touch -->
<!-- internal log4j logging settings. The "null" value for the threshold -->
<!-- attribute can be misleading. The threshold field of a repository	 -->
<!-- cannot be set to null. The "null" value for the threshold attribute -->
<!-- simply means don't touch the threshold field, the threshold field   --> 
<!-- keeps its old value.                                                -->
     
<!ATTLIST log4j:configuration
  xmlns:log4j              CDATA #FIXED "http://jakarta.apache.org/log4j/" 
  threshold                (all|trace|debug|info|warn|error|fatal|off|null) "null"
  debug                    (true|false|null)  "null"
  reset                    (true|false) "false"
>

<!-- renderer elements allow the user to customize the conversion of  -->
<!-- message objects to String.                                       -->

<!ELEMENT renderer EMPTY>
<!ATTLIST renderer
  renderedClass  CDATA #REQUIRED
  renderingClass CDATA #REQUIRED
>

<!-- Appenders must have a name and a class. -->
<!-- Appenders may contain an error handler, a layout, optional parameters -->
<!-- and filters. They may also reference (or include) other appenders. -->
<!ELEMENT appender (errorHandler?, param*,
      rollingPolicy?, triggeringPolicy?, connectionSource?,
      layout?, filter*, appender-ref*)>
<!ATTLIST appender
  name 		CDATA 	#REQUIRED
  class 	CDATA	#REQUIRED
>

<!ELEMENT layout (param*)>
<!ATTLIST layout
  class		CDATA	#REQUIRED
>

<!ELEMENT filter (param*)>
<!ATTLIST filter
  class		CDATA	#REQUIRED
>

<!-- ErrorHandlers can be of any class. They can admit any number of -->
<!-- parameters. -->

<!ELEMENT errorHandler (param*, root-ref?, logger-ref*,  appender-ref?)> 
<!ATTLIST errorHandler
   class        CDATA   #REQUIRED 
>

<!ELEMENT root-ref EMPTY>

<!ELEMENT logger-ref EMPTY>
<!ATTLIST logger-ref
  ref CDATA #REQUIRED
>

<!ELEMENT param EMPTY>
<!ATTLIST param
  name		CDATA   #REQUIRED
  value		CDATA	#REQUIRED
>


<!-- The priority class is org.apache.log4j.Level by default -->
<!ELEMENT priority (param*)>
<!ATTLIST priority
  class   CDATA	#IMPLIED
  value	  CDATA #REQUIRED
>

<!-- The level class is org.apache.log4j.Level by default -->
<!ELEMENT level (param*)>
<!ATTLIST level
  class   CDATA	#IMPLIED
  value	  CDATA #REQUIRED
>


<!-- If no level element is specified, then the configurator MUST not -->
<!-- touch the level of the named category. -->
<!ELEMENT category (param*,(priority|level)?,appender-ref*)>
<!ATTLIST category
  class         CDATA   #IMPLIED
  name		CDATA	#REQUIRED
  additivity	(true|false) "true"  
>

<!-- If no level element is specified, then the configurator MUST not -->
<!-- touch the level of the named logger. -->
<!ELEMENT logger (level?,appender-ref*)>
<!ATTLIST logger
  name		CDATA	#REQUIRED
  additivity	(true|false) "true"  
>


<!ELEMENT categoryFactory (param*)>
<!ATTLIST categoryFactory 
   class        CDATA #REQUIRED>

<!ELEMENT loggerFactory (param*)>
<!ATTLIST loggerFactory
   class        CDATA #REQUIRED>

<!ELEMENT appender-ref EMPTY>
<!ATTLIST appender-ref
  ref CDATA #REQUIRED
>

<!-- plugins must have a name and class and can have optional parameters -->
<!ELEMENT plugin (param*, connectionSource?)>
<!ATTLIST plugin
  name 		CDATA 	   #REQUIRED
  class 	CDATA  #REQUIRED
>

<!ELEMENT connectionSource (dataSource?, param*)>
<!ATTLIST connectionSource
  class        CDATA  #REQUIRED
>

<!ELEMENT dataSource (param*)>
<!ATTLIST dataSource
  class        CDATA  #REQUIRED
>

<!ELEMENT triggeringPolicy ((param|filter)*)>
<!ATTLIST triggeringPolicy
  name 		CDATA  #IMPLIED
  class 	CDATA  #REQUIRED
>

<!ELEMENT rollingPolicy (param*)>
<!ATTLIST rollingPolicy
  name 		CDATA  #IMPLIED
  class 	CDATA  #REQUIRED
>


<!-- If no priority element is specified, then the configurator MUST not -->
<!-- touch the priority of root. -->
<!-- The root category always exists and cannot be subclassed. -->
<!ELEMENT root (param*, (priority|level)?, appender-ref*)>


<!-- ==================================================================== -->
<!--                       A logging event                                -->
<!-- ==================================================================== -->
<!ELEMENT log4j:eventSet (log4j:event*)>
<!ATTLIST log4j:eventSet
  xmlns:log4j             CDATA #FIXED "http://jakarta.apache.org/log4j/" 
  version                (1.1|1.2) "1.2" 
  includesLocationInfo   (true|false) "true"
>



<!ELEMENT log4j:event (log4j:message, log4j:NDC?, log4j:throwable?, 
                       log4j:locationInfo?, log4j:properties?) >

<!-- The timestamp format is application dependent. -->
<!ATTLIST log4j:event
    logger     CDATA #REQUIRED
    level      CDATA #REQUIRED
    thread     CDATA #REQUIRED
    timestamp  CDATA #REQUIRED
    time       CDATA #IMPLIED
>

<!ELEMENT log4j:message (#PCDATA)>
<!ELEMENT log4j:NDC (#PCDATA)>

<!ELEMENT log4j:throwable (#PCDATA)>

<!ELEMENT log4j:locationInfo EMPTY>
<!ATTLIST log4j:locationInfo
  class  CDATA	#REQUIRED
  method CDATA	#REQUIRED
  file   CDATA	#REQUIRED
  line   CDATA	#REQUIRED
>

<!ELEMENT log4j:properties (log4j:data*)>

<!ELEMENT log4j:data EMPTY>
<!ATTLIST log4j:data
  name   CDATA	#REQUIRED
  value  CDATA	#REQUIRED
>

 xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration PUBLIC "-//log4j/log4j Configuration//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    
    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
       <layout class="org.apache.log4j.PatternLayout"> 
          <param name="ConversionPattern" value="%d %-5p %c.%M:%L - %m%n"/> 
       </layout> 
    </appender>
    
    <appender name="FILE" class="org.apache.log4j.DailyRollingFileAppender">
    	<param name="File" value="${catalina.base}/logs/gzyManage/manage"/>
    	<param name="DatePattern" value="'.'yyyy-MM-dd'.log'"/>
    	<layout class="org.apache.log4j.PatternLayout">
    		<param name="ConversionPattern" value="%d %-5p %c.%M:%L - %m%n"/>
    	</layout>
    </appender>
  
     <root>
        <priority value="INFO"/> 
        <appender-ref ref="STDOUT" />
        <appender-ref ref="FILE"/>
     </root> 
    
</log4j:configuration>