3.Web项目中使用Log4j实例

转自：https://blog.csdn.net/luohai859/article/details/52250807

上面代码描述了Log4j的简单应用，其实使用Log4j也就是这样简单方便。当然除了上面的配置方法，还有其它，比如做一个J2EE应用，在J2EE应用使用Log4j，必须先在启动服务时加载Log4j的配置文件进行初始化，可以在web.xml中进行。

1、web应用的log4j使用基本上都采用：新建一个servlet，这个servlet在init函数中为log4j执行配置。一般就是读入配置文件。所以需要在web.xml中为这个servlet配置，同时设定load-on-startup为1。

2、这个servlet配置log4j就是读出配置文件，然后调用configure函数。这里有两个问题：一、需要知道文件在哪里；二、需要正确的文件类型

3、配置文件位置在web.xml中配置一个param即可，路径一般是相对于web的root目录

4、文件类型一般有两种，一个是Java的property文件，另一种是xml文件

配置文件的大致内容：log4j可以指定输出的log级别的最低等级，以及log的输出配置格式，每个log可以指定多个输出方式

（1）创建Web工程，整个工程最后目录如下

（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>  

    <!--用来启动 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容器一来就初始化的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日志设置信息");
        String log4jLocation = config.getInitParameter("log4j-properties-location");  

        ServletContext sc = config.getServletContext();  

        if (log4jLocation == null) {
            System.err.println("*** 没有 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+"初始化日志设置信息");
                PropertyConfigurator.configure(log4jProp);
            } else {
                System.err.println("*** " + log4jProp + " 文件没有找到， 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
    }  

}

调用日志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 {
        // 记录debug级别的信息
        logger.debug("This is debug message.");
        // 记录info级别的信息
        logger.info("This is info message.");
        // 记录error级别的信息
        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);
    }  

}

接下来就是运行了，来看看结果：

输出结果：