1.slf4j 源码分析
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
private Logger log = LoggerFactory.getLogger(this.getClass());
1.1 getLogger方法解析
public static Logger getLogger(Class<?> clazz) {
Logger logger = getLogger(clazz.getName());
if (DETECT_LOGGER_NAME_MISMATCH) {
Class<?> autoComputedCallingClass = Util.getCallingClass();
if (autoComputedCallingClass != null && nonMatchingClasses(clazz, autoComputedCallingClass)) {
Util.report(String.format("Detected logger name mismatch. Given name: \"%s\"; computed name: \"%s\".", logger.getName(),
autoComputedCallingClass.getName()));
Util.report("See " + LOGGER_NAME_MISMATCH_URL + " for an explanation");
}
}
return logger;
}
后半段逻辑 ：当传进来的clazz和调用方的class名字不一致时是否打印警告信息（默认不打印）、
1.2getLogger方法的具体实现：
public static Logger getLogger(String name) {
ILoggerFactory iLoggerFactory = getILoggerFactory();
return iLoggerFactory.getLogger(name);
}
通过getILoggerFactory获取对应的工厂实现类，继而获取对应的log对象
1.3getILoggerFactory方法详解
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:
// support re-entrant behavior.
// See also http://jira.qos.ch/browse/SLF4J-97
return SUBST_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
首次执行performInitialization进行初始化，根据INITIALIZATION_STATE的值进入不同操作（初始化成功即可返回对用的工厂类，继而获取对应log对象）
1.4performInitialization方法说明
private final static void performInitialization() {
bind();
if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
versionSanityCheck();
}
}
bind为实际performInitialization的方法，versionSanityCheck只是进行了jdk版本校验，不再次详述
1.5bind
private final static void bind() {
try {
Set<URL> staticLoggerBinderPathSet = null;
// skip check under android, see also
// http://jira.qos.ch/browse/SLF4J-328
if (!isAndroid()) {
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
// the next line does the binding
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
reportActualBinding(staticLoggerBinderPathSet);
fixSubstituteLoggers();
replayEvents();
// release all resources in SUBST_FACTORY
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);
}
}
bind中关键方法
findPossibleStaticLoggerBinderPathSet();–寻找绑定路径
StaticLoggerBinder.getSingleton();–进行绑定获取工厂方法
fixSubstituteLoggers();–没明白是什么作用，有大佬看到望指点下
replayEvents();–没明白是什么作用，有大佬看到望指点下
1.5.1findPossibleStaticLoggerBinderPathSet
static Set<URL> findPossibleStaticLoggerBinderPathSet() {
// use Set instead of list in order to deal with bug #138
// LinkedHashSet appropriate here because it preserves insertion order
// during iteration
Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
try {
ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
Enumeration<URL> paths;
if (loggerFactoryClassLoader == null) {
paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
} else {
paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
}
while (paths.hasMoreElements()) {
URL path = paths.nextElement();
staticLoggerBinderPathSet.add(path);
}
} catch (IOException ioe) {
Util.report("Error getting resources from path", ioe);
}
return staticLoggerBinderPathSet;
}
获取所有org/slf4j/impl/StaticLoggerBinder.class类的路径（获取大于1个时进行警告但仅仅是警告不影响运行）
详见官方文档说明：
The warning emitted by SLF4J is just that, a warning. Even when multiple bindings are present, SLF4J will pick one logging
framework/implementation and bind with it. The way SLF4J picks a
binding is determined by the JVM and for all practical purposes should
be considered random. As of version 1.6.6, SLF4J will name the
framework/implementation class it is actually bound to.
Embedded components such as libraries or frameworks should not declare a dependency on any SLF4J binding but only depend on
slf4j-api. When a library declares a compile-time dependency on a
SLF4J binding, it imposes that binding on the end-user, thus negating
SLF4J’s purpose. When you come across an embedded component declaring
a compile-time dependency on any SLF4J binding, please take the time
to contact the authors of said component/library and kindly ask them
to mend their ways.
1.5.2（slf4j关键）
StaticLoggerBinder类即使用所有findPossibleStaticLoggerBinderPathSet找到的路径中的一个类（具体根据jvm加载类的顺序，据本人实验所得该顺序即为引用jar的顺序，例如同时引入了slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar , logback-classic.jar，会使用slf4j-nop.jar中的StaticLoggerBinder来获取对应的工厂类）
至于slf4j-api.源码中StaticLoggerBinder类其实在打出的jar包slf4j-api.jar中是不存在的因为他的pom文件中写了，在打包时会删除源码中impl的目录以及其下文件。
1.5.3 reportActualBinding
输出实际（绑定）使用的StaticLoggerBinder
