基本描述
slf4j 是日志的api 门面模式,引入slf4j-api就行,但是打印不出日志的,因为没有具体的实现类。
logback实现包 :
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.6</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.2.6</version>
</dependency>
log4j 实现包 :
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.2</version>
</dependency>
slf4j是怎么找到实现类的
- 通过StaticLoggerBinder 来获取ILoggerFactory
- StaticLoggerBinder类是sf4j-api没有的,需要实现类的jar包提供,并且包名是org.slf4j.impl
- 如果没有实现包,就找不到StaticLoggerBinder类了,就报slf4j Failed to load class “org.slf4j.impl.StaticLoggerBinder”
- 如果有多个实现包,pom依赖谁在前面,就先找到谁的。
相关源码
Logger logger = LoggerFactory.getLogger("aa");
public static Logger getLogger(String name) {
ILoggerFactory iLoggerFactory = getILoggerFactory();
return iLoggerFactory.getLogger(name);
}
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == UNINITIALIZED) {
synchronized (LoggerFactory.class) {
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITIALIZATION;
performInitialization();
}
}
}
switch (INITIALIZATION_STATE) {
case SUCCESSFUL_INITIALIZATION:
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case NOP_FALLBACK_INITIALIZATION:
return NOP_FALLBACK_FACTORY;
case FAILED_INITIALIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITIALIZATION:
return SUBST_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
private final static void performInitialization() {
bind();
if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
versionSanityCheck();
}
}
private final static void bind() {
try {
Set<URL> staticLoggerBinderPathSet = null;
if (!isAndroid()) {
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
reportActualBinding(staticLoggerBinderPathSet);
fixSubstituteLoggers();
replayEvents();
SUBST_FACTORY.clear();
} catch (NoClassDefFoundError ncde) {
String msg = ncde.getMessage();
if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
} else {
failedBinding(ncde);
throw ncde;
}
} catch (java.lang.NoSuchMethodError nsme) {
String msg = nsme.getMessage();
if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) {
INITIALIZATION_STATE = FAILED_INITIALIZATION;
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 nsme;
} catch (Exception e) {
failedBinding(e);
throw new IllegalStateException("Unexpected initialization failure", e);
}
}
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