Log4j详细教程

/**
 * 
 * @类名称：Test
 * @类描述：测试
 * @创建人：zender
 */
public class Test {
    private static Logger log = Logger.getLogger(Test.class);
    public static void main(String[] args) {
        // 记录debug级别的信息  
        log.debug("这是 debug 信息.");  
        // 记录info级别的信息  
        log.info("这是 info 信息.");  
        // 记录error级别的信息  
        log.error("这是 error 信息.");  
    }
}

/**
 * 
 * @类名称：PathUtils
 * @类描述：获取web应用路径
 * @创建人：zender
 */
public class PathUtils {
    private static String webroot = null;
    static {
        webroot = getWebrootPath();
    }
 
    private final static String getWebrootPath() {
        String root = PathUtils.class.getResource("/").getFile();
        try {
            root = new File(root).getParentFile().getParentFile().getCanonicalPath();
            root += File.separator;
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return root;
    }
 
    /**
     * 返回Web应用的路径
     * @return
     */
    public static String webRoot() {
        return webroot;
    }
}

/**
 * 
 * @类名称：InitServlet
 * @类描述：初始化Log4j
 * @创建人：zender
 */
public class InitServlet extends HttpServlet {
    private static final long serialVersionUID = -9074849844731671080L;
    static {
        // 获取web应用路径
        String root = PathUtils.webRoot();
        String logFilesPath = root + "WEB-INF" + File.separator;
        System.setProperty("logFilesPath", logFilesPath);
    }
 
    @Override
    public void init() throws ServletException {
        System.out.println("InitServlet 正在初始化 log4j日志设置信息.");
        super.init();
        String prefix = getServletContext().getRealPath("/");
        String log4jFile = getServletConfig().getInitParameter("log4j");
        // 获取Log4j配置文件路径
        String log4jConfigPath = prefix + log4jFile;
        // 设置Log4j配置文件
        PropertyConfigurator.configure(log4jConfigPath);
    }
}

<?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>Log4jWeb</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>
 
    <servlet>
        <servlet-name>initServlet</servlet-name>
        <servlet-class>com.zender.servlet.InitServlet</servlet-class>
        <init-param>
            <param-name>log4j</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>initServlet</servlet-name>
        <url-pattern>/initServlet.do</url-pattern>
    </servlet-mapping>
</web-app>

/**
 * 
 * @类名称：Log4JTestServlet
 * @类描述：测试Log4j的Servlet
 * @创建人：zender
 */
@WebServlet("/log4JTestServlet")
public class Log4JTestServlet extends HttpServlet {
    private static final long serialVersionUID = 8827404827021162856L;
    private static Logger log = Logger.getLogger(Log4JTestServlet.class);
 
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 记录debug级别的信息
        log.debug("这是 debug 信息.");
        // 记录info级别的信息
        log.info("这是 info 信息.");
        // 记录error级别的信息
        log.error("这是 error 信息.");
        resp.setCharacterEncoding("UTF-8");
        PrintWriter out = resp.getWriter();
        out.write("访问成功！");
    }
}

/**
 * 
 * @类名称：MyServletContextListener
 * @类描述：用于初始化log4j监听器
 * @创建人：zender
 */
public class MyServletContextListener implements ServletContextListener {
    static {
        // 获取web应用路径
        String root = PathUtils.webRoot();
        String logFilesPath = root + "WEB-INF" + File.separator;
        System.setProperty("logFilesPath", logFilesPath);
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
    }
 
    @Override
    //初始化方法
    public void contextInitialized(ServletContextEvent arg0) {
        System.out.println("MyServletContextListener 正在初始化 log4j日志设置信息.");
        ServletContext ctx = arg0.getServletContext();
        String prefix = ctx.getRealPath("/");
        String log4jFile = ctx.getInitParameter("log4j");
        //// 获取Log4j配置文件路径
        String log4jConfigPath = prefix + log4jFile;
        //// 设置Log4j配置文件
        PropertyConfigurator.configure(log4jConfigPath);
    }
}

<?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>Log4jWeb</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>
    
    <context-param>
        <param-name>log4j</param-name>
        <param-value>/WEB-INF/classes/log4j.properties</param-value>
    </context-param>
    <!-- 用于初始化log4j的监听器 -->
    <listener>
        <listener-class>com.zender.listener.MyServletContextListener</listener-class>
    </listener>
</web-app>