1.log4j
/**
* @description: 定制静态日志基础类
* @author: mufeng
* @create: 2020/4/7 10:26
*/
public class BaseLogger {
static {
InputStream in = BaseLogger.class.getClassLoader().getResourceAsStream("log4j.properties");
Properties properties=new Properties();
try {
properties.load(in);
PropertyConfigurator.configure(properties);
in.close();
logger = Logger.getLogger("Logger");
} catch (IOException e) {
e.printStackTrace();
}
}
private static Logger logger;
static final String FQCN = BaseLogger.class.getName();
public static void info(String msg, Object... args){
if(logger.isInfoEnabled()){
FormattingTuple ft = MessageFormatter.arrayFormat(msg, args);
logger.log(FQCN, Level.INFO,ft.getMessage(),ft.getThrowable());
}
}
}
Logger logger= LoggerFactory.getLogger(Test1.class);
日志输出：
test1：
11:05:59,145 INFO Test1:21 - 1213
test2：
11:05:59,145 INFO Test1:21 - 1213
可以看出日志输出是一样的。
实现原理：
通过Logger logger= LoggerFactory.getLogger(Test1.class)追溯源代码
LoggerFactory中 getILoggerFactory执行performInitialization方法，会调用bind方法
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == 0) {
Class var0 = LoggerFactory.class;
synchronized(LoggerFactory.class) {
if (INITIALIZATION_STATE == 0) {
INITIALIZATION_STATE = 1;
performInitialization();
}
}
}
switch(INITIALIZATION_STATE) {
case 1:
return SUBST_FACTORY;
case 2:
throw new IllegalStateException("org.slf4j.LoggerFactory in failed state. Original exception was thrown EARLIER. See also http://www.slf4j.org/codes.html#unsuccessfulInit");
case 3:
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case 4:
return NOP_FALLBACK_FACTORY;
default:
throw new IllegalStateException("Unreachable code");
}
}
findPossibleStaticLoggerBinderPathSet找出类路径所有路径集合，StaticLoggerBinder.getSingleton();存在多个会选择一个。（http://www.slf4j.org/codes.html#multiple_bindings解释：by the JVM and for all practical purposes should be considered random）
日志输出可以看出：
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/persist/maven_Repositories/org/slf4j/slf4j-log4j12/1.7.26/slf4j-log4j12-1.7.26.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/persist/maven_Repositories/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
private static final void bind() {
String msg;
try {
Set<URL> staticLoggerBinderPathSet = null;
if (!isAndroid()) {
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = 3;
reportActualBinding(staticLoggerBinderPathSet);
fixSubstituteLoggers();
replayEvents();
SUBST_FACTORY.clear();
} catch (NoClassDefFoundError var2) {
msg = var2.getMessage();
if (!messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
failedBinding(var2);
throw var2;
}
INITIALIZATION_STATE = 4;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.");
} catch (NoSuchMethodError var3) {
msg = var3.getMessage();
if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) {
INITIALIZATION_STATE = 2;
Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
Util.report("Your binding is version 1.5.5 or earlier.");
Util.report("Upgrade your binding to version 1.6.x.");
}
throw var3;
} catch (Exception var4) {
failedBinding(var4);
throw new IllegalStateException("Unexpected initialization failure", var4);
}
}
得出：logger为Log4jLoggerFactory类getLogger方法得到的实例（Log4jLoggerAdapter）
public Logger getLogger(String name) {
Logger slf4jLogger = (Logger)this.loggerMap.get(name);
if (slf4jLogger != null) {
return slf4jLogger;
} else {
org.apache.log4j.Logger log4jLogger;
if (name.equalsIgnoreCase("ROOT")) {
log4jLogger = LogManager.getRootLogger();
} else {
log4jLogger = LogManager.getLogger(name);
}
Logger newInstance = new Log4jLoggerAdapter(log4jLogger);
Logger oldInstance = (Logger)this.loggerMap.putIfAbsent(name, newInstance);
return (Logger)(oldInstance == null ? newInstance : oldInstance);
}
}
logger.info()实际调用Log4jLoggerAdapter类中的info方法
log4j怎么找到log4j.properties配置文件？
LogManager类存在static静态块，获取了配置信息，LogManager.getLogger(name)获取调起
（PropertyConfigurator.doConfigure方法解析log4j.properties）
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.");
}
}