【Spring】Spring在JavaWeb工程中整合log4j

在《【Spring】Spring3.0.5的下载、配置与Helloworld》（点击打开链接）一文各位已经可能看到了。如果Spring不整合log4j直接启动，则会出现如下关于Spring整合log4j的警告。这个挺烦人的，一方面自己提倡高内聚，低耦合，另一方面，自己没有整合log4j就提出警告。我们程序猿写出来的程序就叫做“耦合”，它Spring就叫做“整合”。好吧！你只能同时搞明白，log4j是个什么鬼东西，Spring怎么整合log4j，两个问题：

log4j:WARN No appenders could be found for logger (org.springframework.web.context.ContextLoader). 
log4j:WARN Please initialize the log4j system properly.

由于此前介绍的都是Spring在Java工程中简单示例，log4j必须在JavaWeb工程中运行才有意义，你同时还要搞明白Spring怎么在JavaWeb工程上面运行，Spring怎么在JavaWeb工程中整合log4j。

一、Spring与Log4j的下载

1、你首先要有这两个JavaWeb组件的jar包吧？不然怎么搞出来？Spring在《【Spring】Spring3.0.5的下载、配置与Helloworld》（点击打开链接）一文中已经讲过怎么下载了。Log4j则打开Apache的官网（点击打开链接）如下图，选择log4j-1.2.17.zip（Windows）或者log4j-1.2.17.tar.gz（Linux）。同样是Apache的东西，在一些高版本的Tomcat中还整合了这个东西，当然，你最好还是在WEB-INF\lib目录下补上这个包，以致于你的工程在所有Tomcat都能跑。

2、在Eclipse for JavaEE中新建一个名为SpringLog4j的Dynamic Web Project，还在解压之后，把spring-framework-3.0.5.RELEASE-dependencies的所有东西与spring-framework-3.0.5.RELEASE\dist中的所有Jar包，不包括那个LIBD文件，apache-log4j-1.2.17下的log4j-1.2.17.jar，拷贝到WEB\lib文件夹。

3、之后你的Eclipse for JavaEE如下所示。WEB-INF目录下的Web.xml、applicationContext.xml、log4j.properties与根目录下的Log4j.jsp是一会儿我们要写的东西。

二、Spring与Log4j的配置

1、Web.xml

首先是这个关于JavaWeb的工程的总配置位置。我们要在里面声明要使用Spring与Log4j。值得注意的Log4j的配置必须在Spring配置之前，否则如果先启动Spring，那个必须整合Log4j才不吐警告的Spring，由于Log4j还没有启动，找不到Spring，又会在任性地吐警告。当然，你设置那些什么优先级也行，不过，先启动的直接放前面，这个文件不是更好看吗？

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">
	<!-- Log4j配置 -->
	<listener>
		<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
	</listener>
	<!-- 指定Log4j的配置文件所在目录。默认配置在WEB-INF目录下 -->
	<context-param>
		<param-name>log4jConfigLocation</param-name>
		<param-value>/WEB-INF/log4j.properties</param-value>
	</context-param>
	
	<!-- Spring配置 -->
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

	<!-- 指定Spring Bean的配置文件所在目录。默认配置在WEB-INF目录下 -->
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/applicationContext.xml</param-value>
	</context-param>
	
</web-app>  

2、log4j.properties

这家伙的后缀名是这么长，你有什么办法？必须照打，都是Linux那边带过来的主，你看看人家Windows的配置文件的后缀名仅仅就是ini3个字母！

#log4j.rootLogger = [ level ] , appenderName, appenderName, ...
log4j.rootLogger = all, console, R

#Console
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [%c]-[%p] %m%n

#File
log4j.appender.R = org.apache.log4j.RollingFileAppender
log4j.appender.R.File = c:/log.txt
log4j.appender.R.MaxFileSize = 500KB
log4j.appender.R.MaxBackupIndex = 1
log4j.appender.R.layout = org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%-d{yyyy-MM-dd HH:mm:ss} [%c]-[%p] - %m%n

这东西还加不了中文注释，给大家一行一行地讲。#后面还仅能写英文的东西，把我大天朝的程序猿放哪里？我就加个中文注释都不让！

首先第一部分是log4j的总配置部分，all代表debug,info,error,fatal四种类型的信息都会输出。一般不设置为all，这里只是为了让大家看到效果。因为那些debug,info信息对我们半点意义没有，还因为有很多系统内部的文件运行都会输出debug与info信息刷屏、刷版。关键是输出到磁盘的日志文件会极速递增，浪费磁盘空间。玩SQL Server的时候大家又不知道那个.ldb是多么恐怖？

因此第一部分，一般写成：

log4j.rootLogger = ERROR, console, R

代表仅输出error与fatal错误。

之后的console，R分别代表在控制台与文件输出。同时在之后的代码必须配置好这个两输出。

第二部分控制台#Console
首先要使用log4j特定的包，这个没有什么好说，最后一句指明输出格式。一会儿大招对照输出结果就明白怎么回事了。

第三部分文件#File

log4j.appender.R.File=c:/log.txt是指这个Web工程错误日志皆输出到c:/log.txt。不要像网上那些大神输出一个什么.log后缀，关键是能够直接打开。

之后log4j.appender.R.MaxFileSize = 500KB指明这个log.txt文件大小最多为500KB，如果超过这个大小，自动开一个新文件，而log4j.appender.R.MaxBackupIndex=1指明此工程顶多只能有1个这个的日志文件。多了的话，新内容覆盖旧内容，就像那些闭路电视摄像头一样。

Log4j到这里就搞完了。

3、applicationContext.xml

之后是Spring的部分，由于这次根本就没有用Spring做任何东西，因此，这个applicationContext.xml这样写就行了：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://www.springframework.org/schema/beans"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
</beans>

能删的我都删了。

4、Log4j.jsp

最后是在WebContent根目录下的Log4j.jsp。在里面写入如下代码，整个程序的入口就是这个地方。

Servlet我都不搞了，就是为了让大家直接看清楚问题的关键所在。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="org.apache.log4j.Logger"%>
<%
Logger.getLogger(this.getClass()).fatal("致命错误！");
Logger.getLogger(this.getClass()).error("出错信息！");
Logger.getLogger(this.getClass()).info("普通信息！");
Logger.getLogger(this.getClass()).debug("调试信息！");
%>

三、运行结果

把SpringLog4j这个JavaWeb工程挂到Tomcat里面，运行，之后在任意浏览器输入http://localhost:8080/SpringLog4j/Log4j.jsp，待网页成功加载之后，直接回到Eclipse则得到如下的运行结果，你输入一次网址刷新一次，则输出一次以下结果：

同时，你的C盘，则多出一个log.txt，里面的内容如下，可以看到，在程序运行的时候，Spring的运行会吐出很多无意义的DEBUG、INFO、TRACE的信息，对于我们来说，真正有用的最后面的四句话。因此，可以理解，为何在上面的log4j.properties（这个后缀名又难记，又长，再次鄙视之！）的第一部分一般不写all，只写ERROR，这就只输出ERROR以上等级的错误，也就是ERROR与FATAL。或者写成TRACE，输出TRACE、ERROR与FATAL信息。

2015-05-10 09:54:34 [org.springframework.web.context.ContextLoader]-[INFO] - Root WebApplicationContext: initialization started
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[INFO] - Refreshing Root WebApplicationContext: startup date [Sun May 10 09:54:34 CST 2015]; root of context hierarchy
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.XmlBeanDefinitionReader]-[INFO] - Loading XML bean definitions from ServletContext resource [/WEB-INF/applicationContext.xml]
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.DefaultDocumentLoader]-[DEBUG] - Using JAXP provider [com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl]
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.PluggableSchemaResolver]-[TRACE] - Trying to resolve XML entity with public id [null] and system id [http://www.springframework.org/schema/beans/spring-beans-3.0.xsd]
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.PluggableSchemaResolver]-[DEBUG] - Loading schema mappings from [META-INF/spring.schemas]
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.PluggableSchemaResolver]-[DEBUG] - Loaded schema mappings: {http://www.springframework.org/schema/oxm/spring-oxm-3.0.xsd=org/springframework/oxm/config/spring-oxm-3.0.xsd, http://www.springframework.org/schema/util/spring-util.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd, http://www.springframework.org/schema/jms/spring-jms-3.0.xsd=org/springframework/jms/config/spring-jms-3.0.xsd, http://www.springframework.org/schema/task/spring-task.xsd=org/springframework/scheduling/config/spring-task-3.0.xsd, http://www.springframework.org/schema/aop/spring-aop-3.0.xsd=org/springframework/aop/config/spring-aop-3.0.xsd, http://www.springframework.org/schema/aop/spring-aop-2.0.xsd=org/springframework/aop/config/spring-aop-2.0.xsd, http://www.springframework.org/schema/oxm/spring-oxm.xsd=org/springframework/oxm/config/spring-oxm-3.0.xsd, http://www.springframework.org/schema/tool/spring-tool-2.5.xsd=org/springframework/beans/factory/xml/spring-tool-2.5.xsd, http://www.springframework.org/schema/beans/spring-beans.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd, http://www.springframework.org/schema/jee/spring-jee-2.5.xsd=org/springframework/ejb/config/spring-jee-2.5.xsd, http://www.springframework.org/schema/aop/spring-aop.xsd=org/springframework/aop/config/spring-aop-3.0.xsd, http://www.springframework.org/schema/beans/spring-beans-2.0.xsd=org/springframework/beans/factory/xml/spring-beans-2.0.xsd, http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd=org/springframework/web/servlet/config/spring-mvc-3.0.xsd, http://www.springframework.org/schema/beans/spring-beans-3.0.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd, http://www.springframework.org/schema/task/spring-task-3.0.xsd=org/springframework/scheduling/config/spring-task-3.0.xsd, http://www.springframework.org/schema/tx/spring-tx-2.5.xsd=org/springframework/transaction/config/spring-tx-2.5.xsd, http://www.springframework.org/schema/context/spring-context-2.5.xsd=org/springframework/context/config/spring-context-2.5.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc-3.0.xsd=org/springframework/jdbc/config/spring-jdbc-3.0.xsd, http://www.springframework.org/schema/tool/spring-tool-3.0.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd, http://www.springframework.org/schema/tx/spring-tx.xsd=org/springframework/transaction/config/spring-tx-3.0.xsd, http://www.springframework.org/schema/tool/spring-tool-2.0.xsd=org/springframework/beans/factory/xml/spring-tool-2.0.xsd, http://www.springframework.org/schema/util/spring-util-2.5.xsd=org/springframework/beans/factory/xml/spring-util-2.5.xsd, http://www.springframework.org/schema/lang/spring-lang.xsd=org/springframework/scripting/config/spring-lang-3.0.xsd, http://www.springframework.org/schema/lang/spring-lang-2.5.xsd=org/springframework/scripting/config/spring-lang-2.5.xsd, http://www.springframework.org/schema/jee/spring-jee-3.0.xsd=org/springframework/ejb/config/spring-jee-3.0.xsd, http://www.springframework.org/schema/jee/spring-jee-2.0.xsd=org/springframework/ejb/config/spring-jee-2.0.xsd, http://www.springframework.org/schema/context/spring-context.xsd=org/springframework/context/config/spring-context-3.0.xsd, http://www.springframework.org/schema/jee/spring-jee.xsd=org/springframework/ejb/config/spring-jee-3.0.xsd, http://www.springframework.org/schema/jms/spring-jms-2.5.xsd=org/springframework/jms/config/spring-jms-2.5.xsd, http://www.springframework.org/schema/jms/spring-jms.xsd=org/springframework/jms/config/spring-jms-3.0.xsd, http://www.springframework.org/schema/aop/spring-aop-2.5.xsd=org/springframework/aop/config/spring-aop-2.5.xsd, http://www.springframework.org/schema/mvc/spring-mvc.xsd=org/springframework/web/servlet/config/spring-mvc-3.0.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc.xsd=org/springframework/jdbc/config/spring-jdbc-3.0.xsd, http://www.springframework.org/schema/tx/spring-tx-2.0.xsd=org/springframework/transaction/config/spring-tx-2.0.xsd, http://www.springframework.org/schema/tx/spring-tx-3.0.xsd=org/springframework/transaction/config/spring-tx-3.0.xsd, http://www.springframework.org/schema/context/spring-context-3.0.xsd=org/springframework/context/config/spring-context-3.0.xsd, http://www.springframework.org/schema/tool/spring-tool.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd, http://www.springframework.org/schema/util/spring-util-3.0.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd, http://www.springframework.org/schema/lang/spring-lang-3.0.xsd=org/springframework/scripting/config/spring-lang-3.0.xsd, http://www.springframework.org/schema/util/spring-util-2.0.xsd=org/springframework/beans/factory/xml/spring-util-2.0.xsd, http://www.springframework.org/schema/lang/spring-lang-2.0.xsd=org/springframework/scripting/config/spring-lang-2.0.xsd, http://www.springframework.org/schema/beans/spring-beans-2.5.xsd=org/springframework/beans/factory/xml/spring-beans-2.5.xsd}
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.PluggableSchemaResolver]-[DEBUG] - Found XML schema [http://www.springframework.org/schema/beans/spring-beans-3.0.xsd] in classpath: org/springframework/beans/factory/xml/spring-beans-3.0.xsd
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader]-[DEBUG] - Loading bean definitions
2015-05-10 09:54:34 [org.springframework.beans.factory.xml.XmlBeanDefinitionReader]-[DEBUG] - Loaded 0 bean definitions from location pattern [/WEB-INF/applicationContext.xml]
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[DEBUG] - Bean factory for Root WebApplicationContext: org.springframework.beans.factory.support.DefaultListableBeanFactory@5eedf162: defining beans []; root of factory hierarchy
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[DEBUG] - Unable to locate MessageSource with name 'messageSource': using default [org.springframework.context.support.DelegatingMessageSource@314b0824]
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[DEBUG] - Unable to locate ApplicationEventMulticaster with name 'applicationEventMulticaster': using default [org.springframework.context.event.SimpleApplicationEventMulticaster@708a538f]
2015-05-10 09:54:34 [org.springframework.ui.context.support.UiApplicationContextUtils]-[DEBUG] - Unable to locate ThemeSource with name 'themeSource': using default [org.springframework.ui.context.support.ResourceBundleThemeSource@1fce66ba]
2015-05-10 09:54:34 [org.springframework.beans.factory.support.DefaultListableBeanFactory]-[INFO] - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@5eedf162: defining beans []; root of factory hierarchy
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[DEBUG] - Unable to locate LifecycleProcessor with name 'lifecycleProcessor': using default [org.springframework.context.support.DefaultLifecycleProcessor@7cbc2c83]
2015-05-10 09:54:34 [org.springframework.beans.factory.support.DefaultListableBeanFactory]-[DEBUG] - Returning cached instance of singleton bean 'lifecycleProcessor'
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[TRACE] - Publishing event in Root WebApplicationContext: org.springframework.context.event.ContextRefreshedEvent[source=Root WebApplicationContext: startup date [Sun May 10 09:54:34 CST 2015]; root of context hierarchy]
2015-05-10 09:54:34 [org.springframework.web.context.ContextLoader]-[DEBUG] - Published root WebApplicationContext as ServletContext attribute with name [org.springframework.web.context.WebApplicationContext.ROOT]
2015-05-10 09:54:34 [org.springframework.web.context.ContextLoader]-[INFO] - Root WebApplicationContext: initialization completed in 230 ms
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[FATAL] - 致命错误！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[ERROR] - 出错信息！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[INFO] - 普通信息！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[DEBUG] - 调试信息！

四、总结

Log4j一般不会像这样直接写在log4j.jsp中。一般处于那些try-catch异常结构中的catch里面，或许一些操作文件、数据库的关键数据之间，直接给程序员看的。程序猿有空看看那个在log.txt，也就像保安有空看看闭路电视，来确定你的WEB工程到底正不正常。可以成为系统运维的一部分。