上面代碼描述了Log4j的簡單應用，其實使用Log4j也就是這樣簡單方便。當然除了上面的配置方法，還有其它，比如做一個J2EE應用，在J2EE應用使用Log4j，必須先在啟動服務時加載Log4j的配置文件進行初始化，可以在web.xml中進行。 1、web應用的log4j使用基本上都采用：新建一個servlet，這個servlet在init函數中為log4j執行配置。一般就是讀入配置文件。所以需要在web.xml中為這個servlet配置，同時設定load-on-startup為1。 2、這個servlet配置log4j就是讀出配置文件，然后調用configure函數。這里有兩個問題：一、需要知道文件在哪里；二、需要正確的文件類型 3、配置文件位置在web.xml中配置一個param即可，路徑一般是相對于web的root目錄 4、文件類型一般有兩種，一個是Java的property文件，另一種是xml文件 配置文件的大致內容：log4j可以指定輸出的log級別的最低等級，以及log的輸出配置格式，每個log可以指定多個輸出方式 (1) 創建Web工程，整個工程最后目錄如下  (2）web.xml配置如下： ~~~ <?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" id="WebApp_ID" version="3.0"> <display-name>LogLearning</display-name> <servlet> <servlet-name>Log4JTestServlet</servlet-name> <servlet-class>com.mucfc.Log4JTestServlet</servlet-class> </servlet> <!--用來啟動 log4jConfigLocation的servlet --> <servlet> <servlet-name>Log4JInitServlet</servlet-name> <servlet-class>com.mucfc.Log4JInitServlet</servlet-class> <init-param> <param-name>log4j-properties-location</param-name> <param-value>/WEB-INF/classes/log4j.properties</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>Log4JTestServlet</servlet-name> <url-pattern>/test</url-pattern> </servlet-mapping> </web-app> ~~~ （3）配置文件log4j.properties ~~~ ### set log levels ### log4j.rootLogger = debug,stdout,D,E log4j.appender.stdout = org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target = System.out log4j.appender.stdout.layout = org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n log4j.appender.D = org.apache.log4j.DailyRollingFileAppender log4j.appender.D.File = F://logs/log.log log4j.appender.D.Append = true log4j.appender.D.Threshold = DEBUG log4j.appender.D.layout = org.apache.log4j.PatternLayout log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n log4j.appender.E = org.apache.log4j.DailyRollingFileAppender log4j.appender.E.File =F://logs/error.log log4j.appender.E.Append = true log4j.appender.E.Threshold = ERROR log4j.appender.E.layout = org.apache.log4j.PatternLayout log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n ~~~ (4) web容器一來就初始化的servlet Log4JInitServlet.java ~~~ package com.mucfc; import java.io.File; import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.log4j.BasicConfigurator; import org.apache.log4j.PropertyConfigurator; /** * Servlet implementation class Log4JInitServlet */ @WebServlet("/Log4JInitServlet") public class Log4JInitServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public Log4JInitServlet() { super(); // TODO Auto-generated constructor stub } /** * @see Servlet#init(ServletConfig) */ public void init(ServletConfig config) throws ServletException { System.out.println("Log4JInitServlet 正在初始化 log4j日志設置信息"); String log4jLocation = config.getInitParameter("log4j-properties-location"); ServletContext sc = config.getServletContext(); if (log4jLocation == null) { System.err.println("*** 沒有 log4j-properties-location 初始化的文件, 所以使用 BasicConfigurator初始化"); BasicConfigurator.configure(); } else { String webAppPath = sc.getRealPath("/"); String log4jProp = webAppPath + log4jLocation; File yoMamaYesThisSaysYoMama = new File(log4jProp); if (yoMamaYesThisSaysYoMama.exists()) { System.out.println("使用: " + log4jProp+"初始化日志設置信息"); PropertyConfigurator.configure(log4jProp); } else { System.err.println("*** " + log4jProp + " 文件沒有找到， 所以使用 BasicConfigurator初始化"); BasicConfigurator.configure(); } } super.init(config); } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } } ~~~ 調用日志Log4JTestServlet,java ~~~ package com.mucfc; import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.log4j.Logger; /** * Servlet implementation class Log4JTestServlet */ @WebServlet("/Log4JTestServlet") public class Log4JTestServlet extends HttpServlet { private static final long serialVersionUID = 1L; private static Logger logger = Logger.getLogger(Log4JTestServlet.class); /** * @see HttpServlet#HttpServlet() */ public Log4JTestServlet() { super(); // TODO Auto-generated constructor stub } /** * @see Servlet#init(ServletConfig) */ public void init(ServletConfig config) throws ServletException { // TODO Auto-generated method stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 記錄debug級別的信息 logger.debug("This is debug message."); // 記錄info級別的信息 logger.info("This is info message."); // 記錄error級別的信息 logger.error("This is error message."); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } } ~~~ 接下來就是運行了，來看看結果：  輸出結果