log4j由三个重要的组件构成:
- 日志信息的输出格式(布局)Layout
- 日志信息的输出目的地 Appender
- 日志信息的优先级 Level
工程中使用配置文件定义输出格式Layout和输出目的地Appender,log4j支持两种方式的配置方式:
- .properties文件
- xml文件
但是工程中最常用的方式还是xml方式的配置。
先看一个实验:
一、工程目录
二、conf/xmllog4jconfig1.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd"> <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> <appender name="appender" class="org.apache.log4j.ConsoleAppender"> <layout class="org.apache.log4j.PatternLayout"> <param name="ConversionPattern" value="[%p|%c{1}] %m%n" /> </layout> </appender> <root> <level value="DEBUG" /> <appender-ref ref="appender" /> </root> </log4j:configuration>
三、Log4jTest.java
package jijian.test; import org.apache.log4j.Logger; import org.apache.log4j.xml.DOMConfigurator; public class Log4jTest { static Logger logger = Logger.getLogger(Log4jTest.class); public static void main(String[] args) { DOMConfigurator.configure("conf/xmllog4jconfig1.xml"); logger.debug("Here is some DEBUG"); logger.info("Here is some INFO"); logger.warn("Here is some WARN"); logger.error("Here is some ERROR"); logger.fatal("Here is some FATAL"); } }
四、实验结果
五、实验可能的异常
1、配置文件的路径要正确,默认搜索路径限于Project1目录,不搜索其子目录
若java文件里写为 DOMConfigurator.configure("xmllog4jconfig1.xml"); 则异常如下
log4j:ERROR Could not parse file [xmllog4jconfig1.xml]. java.io.FileNotFoundException: D:\Workspace\Project1\xmllog4jconfig1.xml (系统找不到指定的文件。) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.<init>(FileInputStream.java:106) at java.io.FileInputStream.<init>(FileInputStream.java:66) at sun.net.www.protocol.file.FileURLConnection.connect(FileURLConnection.java:70) at sun.net.www.protocol.file.FileURLConnection.getInputStream(FileURLConnection.java:161) at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:653) at com.sun.org.apache.xerces.internal.impl.XMLVersionDetector.determineDocVersion(XMLVersionDetector.java:186) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:771) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107) at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:225) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:283) at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:208) at org.apache.log4j.xml.DOMConfigurator$1.parse(DOMConfigurator.java:749) at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:871) at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:755) at org.apache.log4j.xml.DOMConfigurator.configure(DOMConfigurator.java:896) at jijian.test.Log4jTest.main(Log4jTest.java:10) log4j:WARN No appenders could be found for logger (jijian.test.Log4jTest). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
2、xml文件格式要正确,开始 <?xml version="1.0" encoding="UTF-8" ?> 一定要顶行顶格写,前边不能有任何东西
若xml文件里写为
<!-- 此处不能有数据 --> <?xml version="1.0" encoding="UTF-8" ?>
则异常如下
log4j:WARN Fatal parsing error 2 and column 6 log4j:WARN The processing instruction target matching "[xX][mM][lL]" is not allowed. log4j:ERROR Could not parse file [conf/xmllog4jconfig1.xml]. org.xml.sax.SAXParseException: The processing instruction target matching "[xX][mM][lL]" is not allowed. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:239) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:283) at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:208) at org.apache.log4j.xml.DOMConfigurator$1.parse(DOMConfigurator.java:749) at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:871) at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:755) at org.apache.log4j.xml.DOMConfigurator.configure(DOMConfigurator.java:896) at jijian.test.Log4jTest.main(Log4jTest.java:10) log4j:WARN No appenders could be found for logger (jijian.test.Log4jTest). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
可以清楚的看出出错指示是:指令格式不符合标准,导致xml文件无法解析。