在《【Spring】Spring3.0.5的下載、配置與Helloworld》（點選開啟連結）一文各位已經可能看到了。如果Spring不整合log4j直接啟動，則會出現如下關於Spring整合log4j的警告。這個挺煩人的，一方面自己提倡高內聚，低耦合，另一方面，自己沒有整合log4j就提出警告。我們程式猿寫出來的程式就叫做“耦合”，它Spring就叫做“整合”。好吧！你只能同時搞明白，log4j是個什麼鬼東西，Spring怎麼整合log4j，兩個問題：

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

一、Spring與Log4j的下載

1、你首先要有這兩個JavaWeb元件的jar包吧？不然怎麼搞出來？Spring在《【Spring】Spring3.0.5的下載、配置與Helloworld》（點選開啟連結）一文中已經講過怎麼下載了。Log4j則開啟Apache的官網（點選開啟連結）如下圖，選擇log4j-1.2.17.zip（Windows）或者log4j-1.2.17.tar.gz（Linux）。同樣是Apache的東西，在一些高版本的Tomcat中還整合了這個東西，當然，你最好還是在WEB-INF\lib目錄下補上這個包，以致於你的工程在所有Tomcat都能跑。

2、在Eclipse for JavaEE中新建一個名為SpringLog4j的Dynamic Web Project，還在解壓之後，把spring-framework-3.0.5.RELEASE-dependencies的所有東西與spring-framework-3.0.5.RELEASE\dist中的所有Jar包，不包括那個LIBD檔案，apache-log4j-1.2.17下的log4j-1.2.17.jar，拷貝到WEB\lib資料夾。

3、之後你的Eclipse for JavaEE如下所示。WEB-INF目錄下的Web.xml、applicationContext.xml、log4j.properties與根目錄下的Log4j.jsp是一會兒我們要寫的東西。

二、Spring與Log4j的配置

1、Web.xml

首先是這個關於JavaWeb的工程的總配置位置。我們要在裡面宣告要使用Spring與Log4j。值得注意的Log4j的配置必須在Spring配置之前，否則如果先啟動Spring，那個必須整合Log4j才不吐警告的Spring，由於Log4j還沒有啟動，找不到Spring，又會在任性地吐警告。當然，你設定那些什麼優先順序也行，不過，先啟動的直接放前面，這個檔案不是更好看嗎？

<?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的配置檔案所在目錄。預設配置在WEB-INF目錄下 -->
	<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的配置檔案所在目錄。預設配置在WEB-INF目錄下 -->
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/applicationContext.xml</param-value>
	</context-param>
	
</web-app>  

這傢伙的字尾名是這麼長，你有什麼辦法？必須照打，都是Linux那邊帶過來的主，你看看人家Windows的配置檔案的字尾名僅僅就是ini3個字母！

#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

首先第一部分是log4j的總配置部分，all代表debug,info,error,fatal四種類型的資訊都會輸出。一般不設定為all，這裡只是為了讓大家看到效果。因為那些debug,info資訊對我們半點意義沒有，還因為有很多系統內部的檔案執行都會輸出debug與info資訊刷屏、刷版。關鍵是輸出到磁碟的日誌檔案會極速遞增，浪費磁碟空間。玩SQL Server的時候大家又不知道那個.ldb是多麼恐怖？

因此第一部分，一般寫成：

log4j.rootLogger = ERROR, console, R

之後的console，R分別代表在控制檯與檔案輸出。同時在之後的程式碼必須配置好這個兩輸出。

第二部分控制檯#Console
首先要使用log4j特定的包，這個沒有什麼好說，最後一句指明輸出格式。一會兒大招對照輸出結果就明白怎麼回事了。

第三部分檔案#File

log4j.appender.R.File=c:/log.txt是指這個Web工程錯誤日誌皆輸出到c:/log.txt。不要像網上那些大神輸出一個什麼.log字尾，關鍵是能夠直接開啟。

之後log4j.appender.R.MaxFileSize = 500KB指明這個log.txt檔案大小最多為500KB，如果超過這個大小，自動開一個新檔案，而log4j.appender.R.MaxBackupIndex=1指明此工程頂多只能有1個這個的日誌檔案。多了的話，新內容覆蓋舊內容，就像那些閉路電視攝像頭一樣。

Log4j到這裡就搞完了。

3、applicationContext.xml

之後是Spring的部分，由於這次根本就沒有用Spring做任何東西，因此，這個applicationContext.xml這樣寫就行了：

<?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>

4、Log4j.jsp

最後是在WebContent根目錄下的Log4j.jsp。在裡面寫入如下程式碼，整個程式的入口就是這個地方。

Servlet我都不搞了，就是為了讓大家直接看清楚問題的關鍵所在。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="org.apache.log4j.Logger"%>
<%
Logger.getLogger(this.getClass()).fatal("致命錯誤！");
Logger.getLogger(this.getClass()).error("出錯資訊！");
Logger.getLogger(this.getClass()).info("普通訊息！");
Logger.getLogger(this.getClass()).debug("除錯資訊！");
%>

把SpringLog4j這個JavaWeb工程掛到Tomcat裡面，執行，之後在任意瀏覽器輸入http://localhost:8080/SpringLog4j/Log4j.jsp，待網頁成功載入之後，直接回到Eclipse則得到如下的執行結果，你輸入一次網址重新整理一次，則輸出一次以下結果：

同時，你的C盤，則多出一個log.txt，裡面的內容如下，可以看到，在程式執行的時候，Spring的執行會吐出很多無意義的DEBUG、INFO、TRACE的資訊，對於我們來說，真正有用的最後面的四句話。因此，可以理解，為何在上面的log4j.properties（這個字尾名又難記，又長，再次鄙視之！）的第一部分一般不寫all，只寫ERROR，這就只輸出ERROR以上等級的錯誤，也就是ERROR與FATAL。或者寫成TRACE，輸出TRACE、ERROR與FATAL資訊。

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.s[email protected]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 [[email protected]0824]
2015-05-10 09:54:34 [org.springframework.web.context.support.XmlWebApplicationContext]-[DEBUG] - Unable to locate ApplicationEventMulticaster with name 'applicationEventMulticaster': using default [org.[email protected]708a538f]
2015-05-10 09:54:34 [org.springframework.ui.context.support.UiApplicationContextUtils]-[DEBUG] - Unable to locate ThemeSource with name 'themeSource': using default [o[email protected]1fce66ba]
2015-05-10 09:54:34 [org.springframework.beans.factory.support.DefaultListableBeanFactory]-[INFO] - Pre-instantiating singletons in org.s[email protected]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 [[email protected]bc2c83]
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] - 致命錯誤！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[ERROR] - 出錯資訊！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[INFO] - 普通訊息！
2015-05-10 09:54:48 [org.apache.jsp.Log4j_jsp]-[DEBUG] - 除錯資訊！

Log4j一般不會像這樣直接寫在log4j.jsp中。一般處於那些try-catch異常結構中的catch裡面，或許一些操作檔案、資料庫的關鍵資料之間，直接給程式設計師看的。程式猿有空看看那個在log.txt，也就像保安有空看看閉路電視，來確定你的WEB工程到底正不正常。可以成為系統運維的一部分。