slf4j 之logback日志之sl4j架构【二】

一、整体介绍

介绍:

The Simple Logging Facade for Java (SLF4J) serves as a simple facade or abstraction for various logging frameworks (e.g. java.util.logging, logback, log4j) allowing the end user to plug in the desired logging framework at deployment time.

工作模式：

sl4j-api结构图

根据入口代码来分析。

Logger logger = LoggerFactory.getLogger(logbackTest.class);

我们可以知道初始化，是从这个方法开始的。

首先入口代码非常简单

  public static Logger getLogger(String name) {
    ILoggerFactory iLoggerFactory = getILoggerFactory();
    return iLoggerFactory.getLogger(name);
  }
public static ILoggerFactory getILoggerFactory() {
    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://bugzilla.slf4j.org/show_bug.cgi?id=106
        return TEMP_FACTORY;
    }
    throw new IllegalStateException("Unreachable code");
  }

　　

上面基本上就是整个调用流程的代码了。第5行通过factory模式得到了一个日志工厂，第6行根据名字获取日志logger。

第3个函数是主要的逻辑函数，根据INITIALIZATION_STATE 不同状态，做不同的处理。

当INITIALIZATION_STATE ==0时，初始化日志框架【9行】

当INITIALIZATION_STATE ==1时，返回的TEMP_FACTORY，我们尅看下定义【15行】

static SubstituteLoggerFactory TEMP_FACTORY = new SubstituteLoggerFactory();

SubstituteLoggerFactory是什么尼，很简单的结构，是由sl4j实现的一个。。，看一下文档描述：

SubstituteLoggerFactory 简单实现了ILoggerFactory接口，并总是返回一个单例的 NOPLogger实例。

作用：

* It used as a temporary substitute for the real ILoggerFactory during its
* auto-configuration which may re-enter LoggerFactory to obtain logger
* instances. See also http://bugzilla.slf4j.org/show_bug.cgi?id=106

当INITIALIZATION_STATE ==2时，返回的失败信息【17行】，其中我们可以看下各种状态枚举定义，可以知道2对应的状态是日志初始化失败

   static final int ONGOING_INITIALIZATION = 1;
    static final int FAILED_INITIALIZATION = 2;
    static final int SUCCESSFUL_INITIALIZATION = 3;
    static final int NOP_FALLBACK_INITIALIZATION = 4;

当INITIALIZATION_STATE ==3时，返回的失败信息【19行】，显然是日志初始化成功，获取日志单例信息。

当INITIALIZATION_STATE ==4时，返回的失败信息【21行】，我们看见返回会的是NOP_FALLBACK_FACTORY（没有找到桥接jar）对象，看下定义

 static NOPLoggerFactory NOP_FALLBACK_FACTORY = new NOPLoggerFactory();
/**
 * NOPLoggerFactory is an trivial implementation of {@link
 * ILoggerFactory} which always returns the unique instance of
 * NOPLogger.
 *
 * @author Ceki Gülcü
 */
public class NOPLoggerFactory implements ILoggerFactory {

  public NOPLoggerFactory() {
    // nothing to do
  }

  public Logger getLogger(String name) {
    return NOPLogger.NOP_LOGGER;
  }

}

根据定义和和注释，我们我们可以大胆猜测，4状态就是什么都不做，NO Operator Logger Factory.仅仅是一个空实现。

官网描述：SINCE 1.6.0 If no binding is found on the class path, then SLF4J will default to a no-operation implementation.

二、核心代码分析

重点分析这个方法performInitialization()；

   private final static void performInitialization() {
     bind();
     if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
       versionSanityCheck();
     }
   }
 private final static void bind() {
     try {
       Set staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
       reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
       // the next line does the binding
       StaticLoggerBinder.getSingleton();
       INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
       reportActualBinding(staticLoggerBinderPathSet);
       emitSubstituteLoggerWarning();
     } 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.indexOf("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);
     }
   }

首先进入bind方法，

bind方法第9行，findPossibleStaticLoggerBinderPathSet（），根据名字我们知道这个函数的功能是查找可能的StaticLoggerBinder路径集合。

   private static Set findPossibleStaticLoggerBinderPathSet() {
     // 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 = (URL) paths.nextElement();
         staticLoggerBinderPathSet.add(path);
       }
     } catch (IOException ioe) {
       Util.report("Error getting resources from path", ioe);
     }
     return staticLoggerBinderPathSet;
   }

我们可以看到都是在加载StaticLoggerBinder.class类

private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class";

那么StaticLoggerBinder.class是干嘛的尼？传送门：http://skyao.github.io/2014/07/21/slfj4-binding/，后续会对StaticLoggerBinder仔细分析。

bind方法第10行，假设找到多个StaticLoggerBinder.class，就提示输出信息。

bind方法第12行，很关键的一行代码，和第10行关联起来了。获取一个StaticLoggerBinder单例.

  private static StaticLoggerBinder SINGLETON = new StaticLoggerBinder();
  public static StaticLoggerBinder getSingleton() {
     return SINGLETON;
   }
   static {
     SINGLETON.init();
   }
   void init() {
     try {
       try {
         new ContextInitializer(defaultLoggerContext).autoConfig();
       } catch (JoranException je) {
         Util.report("Failed to auto configure default logger context", je);
       }
       // logback-292
       if(!StatusUtil.contextHasStatusListener(defaultLoggerContext)) {
         StatusPrinter.printInCaseOfErrorsOrWarnings(defaultLoggerContext);
       }
       contextSelectorBinder.init(defaultLoggerContext, KEY);
       initialized = true;
     } catch (Throwable t) {
       // we should never get here
       Util.report("Failed to instantiate [" + LoggerContext.class.getName()
           + "]", t);
     }
   }

可以看出其实就是一个单例，并初始化了。初始化的具体详情，我们在后续会分析。这里我们只需要知道得到了一个StaticLoggerBinder单例对象即可。

bind方法14，15，16行主要是改变状态，显示警告信息等。

由此我们知道bind方法核心功能是加载了StaticLoggerBinder.class，并初始化了单例对象。

我们回到上面getILoggerFactory方法。

getILoggerFactory方法19行代码：StaticLoggerBinder.getSingleton().getLoggerFactory();

即StaticLoggerBinder的getLoggerFactory方法，我们看一下定义。

 public ILoggerFactory getLoggerFactory() {
     if (!initialized) {
       return defaultLoggerContext;
     }

     if (contextSelectorBinder.getContextSelector() == null) {
       throw new IllegalStateException(
           "contextSelector cannot be null. See also " + NULL_CS_URL);
     }
     return contextSelectorBinder.getContextSelector().getLoggerContext();
   }

在第二行判断initialized状态在init()方法第20行知道，在初始化完成后，即为true。所以getLoggerFactory方法会直接到第6行。

private final ContextSelectorStaticBinder contextSelectorBinder = ContextSelectorStaticBinder.getSingleton();
public static ContextSelectorStaticBinder getSingleton() {
    return singleton;
}
static ContextSelectorStaticBinder singleton = new ContextSelectorStaticBinder();

第6行获取到一个ContextSelectorStaticBinder的实例。并且获取getContextSelector方法

   public ContextSelector getContextSelector() {
     return contextSelector;
   }
  ContextSelector contextSelector;
 public void init(LoggerContext defaultLoggerContext, Object key) throws ClassNotFoundException,
       NoSuchMethodException, InstantiationException, IllegalAccessException,
       InvocationTargetException  {
     if(this.key == null) {
       this.key = key;
     } else if (this.key != key) {
       throw new IllegalAccessException("Only certain classes can access this method.");
     }

     String contextSelectorStr = OptionHelper
         .getSystemProperty(ClassicConstants.LOGBACK_CONTEXT_SELECTOR);
     if (contextSelectorStr == null) {
       contextSelector = new DefaultContextSelector(defaultLoggerContext);
     } else if (contextSelectorStr.equals("JNDI")) {
       // if jndi is specified, let's use the appropriate class
       contextSelector = new ContextJNDISelector(defaultLoggerContext);
     } else {
       contextSelector = dynamicalContextSelector(defaultLoggerContext,
           contextSelectorStr);
     }
   }

我们查询代码知道getContextSelector获取的对象是在init()中方法赋值的。

在StaticLoggerBinder类中init()方法第19行代码，进行了ContextSelectorStaticBinder的实例化。

contextSelectorBinder.getContextSelector()根据代码知道，其实就是LoggerContext包装对象。

第10代码，contextSelectorBinder.getContextSelector().getLoggerContext();得到一个LoggerContext对象。

即，我们的getILoggerFactory的方法，得到了一个LoggerContext对象。

在getLogger方法第二行代码，传递name获取Logger对象。

  public final Logger getLogger(final String name) {

     if (name == null) {
       throw new IllegalArgumentException("name argument cannot be null");
     }

     // if we are asking for the root logger, then let us return it without
     // wasting time
     if (Logger.ROOT_LOGGER_NAME.equalsIgnoreCase(name)) {
       return root;
     }

     int i = ;
     Logger logger = root;

     // check if the desired logger exists, if it does, return it
     // without further ado.
     Logger childLogger = (Logger) loggerCache.get(name);
     // if we have the child, then let us return it without wasting time
     if (childLogger != null) {
       return childLogger;
     }

     // if the desired logger does not exist, them create all the loggers
     // in between as well (if they don't already exist)
     String childName;
     while (true) {
       int h = LoggerNameUtil.getSeparatorIndexOf(name, i);
       if (h == -) {
         childName = name;
       } else {
         childName = name.substring(, h);
       }
       // move i left of the last point
       i = h + ;
       synchronized (logger) {
         childLogger = logger.getChildByName(childName);
         if (childLogger == null) {
           childLogger = logger.createChildByName(childName);
           loggerCache.put(childName, childLogger);
           incSize();
         }
       }
       logger = childLogger;
       if (h == -) {
         return childLogger;
       }
     }
   }

至此，整个流程就走完了。

下一章，我们会对整个sl4j架构进行分析。分析代码的优缺点。

-------------------------------------------------------------------------华丽分割线，下面是StaticLoggerBinder代码分析-------------------------------

在我们的源码目录中，并没有这个类

那么他在哪里尼？这就是实现接口反转和适配很重要的一个环节了，还记得我们开始第一幅图么

，

sl4j-api会调用

看下类类定StaticLoggerBinder.class：binding一个实际的ILoggerFactory的实例。

* The binding of {@link LoggerFactory} class with an actual instance of
* {@link ILoggerFactory} is performed using information returned by this class.
来吧，一言不合就看源码：

 public class StaticLoggerBinder implements LoggerFactoryBinder {

   /**
    * Declare the version of the SLF4J API this implementation is compiled
    * against. The value of this field is usually modified with each release.
    */
   // to avoid constant folding by the compiler, this field must *not* be final
   public static String REQUESTED_API_VERSION = "1.6"; // !final

   final static String NULL_CS_URL = CoreConstants.CODES_URL + "#null_CS";

   /**
    * The unique instance of this class.
    */
   private static StaticLoggerBinder SINGLETON = new StaticLoggerBinder();

   private static Object KEY = new Object();

   static {
     SINGLETON.init();
   }

   private boolean initialized = false;
   private LoggerContext defaultLoggerContext = new LoggerContext();
   private final ContextSelectorStaticBinder contextSelectorBinder = ContextSelectorStaticBinder
       .getSingleton();

   private StaticLoggerBinder() {
     defaultLoggerContext.setName(CoreConstants.DEFAULT_CONTEXT_NAME);
   }

   public static StaticLoggerBinder getSingleton() {
     return SINGLETON;
   }

   /**
    * Package access for testing purposes.
    */
   static void reset() {
     SINGLETON = new StaticLoggerBinder();
     SINGLETON.init();
   }

   /**
    * Package access for testing purposes.
    */
   void init() {
     try {
       try {
         new ContextInitializer(defaultLoggerContext).autoConfig();
       } catch (JoranException je) {
         Util.report("Failed to auto configure default logger context", je);
       }
       // logback-292
       if(!StatusUtil.contextHasStatusListener(defaultLoggerContext)) {
         StatusPrinter.printInCaseOfErrorsOrWarnings(defaultLoggerContext);
       }
       contextSelectorBinder.init(defaultLoggerContext, KEY);
       initialized = true;
     } catch (Throwable t) {
       // we should never get here
       Util.report("Failed to instantiate [" + LoggerContext.class.getName()
           + "]", t);
     }
   }

   public ILoggerFactory getLoggerFactory() {
     if (!initialized) {
       return defaultLoggerContext;
     }

     if (contextSelectorBinder.getContextSelector() == null) {
       throw new IllegalStateException(
           "contextSelector cannot be null. See also " + NULL_CS_URL);
     }
     return contextSelectorBinder.getContextSelector().getLoggerContext();
   }

   public String getLoggerFactoryClassStr() {
     return contextSelectorBinder.getClass().getName();
   }

 }

先看下类图：