本文共 7085 字，大约阅读时间需要 23 分钟。
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
1.5bindprivate final static void bind() { try { Set 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 SetfindPossibleStaticLoggerBinderPathSet() { // use Set instead of list in order to deal with bug #138 // LinkedHashSet appropriate here because it preserves insertion order // during iteration Set staticLoggerBinderPathSet = new LinkedHashSet (); try { ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader(); Enumeration 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转载地址：http://rwepi.baihongyu.com/