# Log4j Log4j是Apache的一个开源项目，通过使用Log4j，我们可以控制日志信息输送的目的地是控制台、文件等地方； 我们也可以控制每一条日志的输出格式；通过定义每一条日志信息的级别，我们能够更加细致地控制日志的生成过程。 最令人感兴趣的就是，这些可以通过一个配置文件来灵活地进行配置，而不需要修改应用的代码。 以下是 Log4j 结合 slf4j 的配置使用过程 ## Log4j 配置过程 1. 下载如下 jar 文件，jar 包下载网站： http://jareye.com/ * slf4j-api-1.7.25.jar * slf4j-log4j12-1.7.25.jar * log4j-1.2.17.jar 2. 在 Eclipse 的项目上右键定义一个名为 conf 的 source folder 3. 在 conf 文件夹中新建 log4j.properties 文件，内容如下 ~~~ log4j.rootLogger=INFO, stdout , R log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=[QNSL] %d{yyyyMMdd HH:mm:ss,SSS} %p [%t] %C.%M(%L) | %m%n log4j.appender.R=org.apache.log4j.DailyRollingFileAppender log4j.appender.R.File=D:\\demo1.log log4j.appender.R.layout=org.apache.log4j.PatternLayout log4j.appender.R.layout.ConversionPattern=[QNSL] %d{yyyyMMdd HH:mm:ss,SSS} %p [%t] %C.%M(%L) | %m%n log4j.logger.cn=ERROR ~~~ 4. 新建一个 Servlet，程序清单如下 ~~~ package cn.controller; import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.log4j.PropertyConfigurator; public class Log4jServlet extends HttpServlet { private static final long serialVersionUID = 1L; public void init(ServletConfig config) throws ServletException { String prefix = this.getClass().getClassLoader().getResource("/").getPath(); String path = config.getInitParameter("log4j-path"); PropertyConfigurator.configure(prefix + path); } public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { } public void doPost(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { } public void destroy() { } } ~~~ 5. 在 web.xml 中登记 Log4jServlet ~~~ <servlet> <servlet-name>log4j</servlet-name> <servlet-class>cn.controller.Log4jServlet</servlet-class> <init-param> <param-name>log4j-path</param-name> <param-value>log4j.properties</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> ~~~ 6. 使用 Log4j ~~~ package cn.controller.common; import java.io.IOException; 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.slf4j.Logger; import org.slf4j.LoggerFactory; /** * Servlet implementation class LoginServlet */ @WebServlet("/common/LoginServlet.do") public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; private static final Logger logger = LoggerFactory.getLogger(LoginServlet.class); /** * @see HttpServlet#HttpServlet() */ public LoginServlet() { super(); } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { logger.debug("Hello, Log4j"); request.getRequestDispatcher("/WEB-INF/pages/common/login.jsp").forward(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } ~~~