Web项目中如何使用Log4j呢?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，整个工程后目录如下

(2)web.xml配置如下：

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi=“//www.w3.org/2001/XMLSchema-instance”

xmlns="//java.sun.com/xml/ns/javaee"

xsi:schemaLocation="//java.sun.com/xml/ns/javaee //java.sun.com/xml/ns/javaee/web-app_3_0.xsd"

id="WebApp_ID" version="3.0">

<dispaly-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：

 

 

 

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