昨天上线折腾了半天，发现日志始终不能正确打印到指定文件，反而Tomcat的catalina.out打印了业务日志，仔细检查线上log4j配置，未发现任何问题，console日志输入并没有打开。于是迅速使用上次上线包进行替换重新发布，发现问题解决。
考虑到本次上线新依赖了其他系统的jar包，检查该jar后发现，jar包中包含了Log4j.xml！！
log4j为何选择了jar中的log4j.xml而不是自己的log4j.properties文件呢，原因就在log4j的LogManager类中
看段代码:
/** * @deprecated This variable is for internal use only. It will * become package protected in future versions. * */ static public final String DEFAULT_CONFIGURATION_FILE = "log4j.properties";static final String DEFAULT_XML_CONFIGURATION_FILE = "log4j.xml";/** * @deprecated This variable is for internal use only. It will * become private in future versions. * */ static final public String DEFAULT_CONFIGURATION_KEY="log4j.configuration";
以上是LogManager的成员变量。
然后看static模块：
static {// By default we use a DefaultRepositorySelector which always returns 'h'.Hierarchy h = new Hierarchy(new RootLogger((Level) Level.DEBUG));repositorySelector = new DefaultRepositorySelector(h);/** Search for the properties file log4j.properties in the CLASSPATH. */String override =OptionConverter.getSystemProperty(DEFAULT_INIT_OVERRIDE_KEY,null);// if there is no default init override, then get the resource// specified by the user or the default config file.if(override == null || "false".equalsIgnoreCase(override)) {String configurationOptionStr = OptionConverter.getSystemProperty(DEFAULT_CONFIGURATION_KEY,null);String configuratorClassName = OptionConverter.getSystemProperty(CONFIGURATOR_CLASS_KEY,null);URL url = null;// if the user has not specified the log4j.configuration// property, we search first for the file "log4j.xml" and then// "log4j.properties"if(configurationOptionStr == null) {url = Loader.getResource(DEFAULT_XML_CONFIGURATION_FILE);if(url == null) { url = Loader.getResource(DEFAULT_CONFIGURATION_FILE);}} else {try { url = new URL(configurationOptionStr);} catch (MalformedURLException ex) { // so, resource is not a URL: // attempt to get the resource from the class path url = Loader.getResource(configurationOptionStr); }}// If we have a non-null url, then delegate the rest of the// configuration to the OptionConverter.selectAndConfigure// method.if(url != null) {LogLog.debug("Using URL ["+url+"] for automatic log4j configuration.");try {OptionConverter.selectAndConfigure(url, configuratorClassName,LogManager.getLoggerRepository());} catch (NoClassDefFoundError e) {LogLog.warn("Error during default initialization", e);}} else {LogLog.debug("Could not find resource: ["+configurationOptionStr+"].");}} else {LogLog.debug("Default initialization of overridden by " +DEFAULT_INIT_OVERRIDE_KEY + "property.");}} 关键点就在
if(configurationOptionStr == null) {url = Loader.getResource(DEFAULT_XML_CONFIGURATION_FILE);if(url == null) { url = Loader.getResource(DEFAULT_CONFIGURATION_FILE);}}说明log4j优先使用程序制定的配置路径，然后使用类路径下的xml配置文件，然后才选择properties文件。这就是原因，希望对大家有所帮助。
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不要等待机会，而要创造机会。
