slf4j 之logback日志之sl4j架構【二】

一、整體介紹

介紹:

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結構圖

根據入口代碼來分析。

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

我們可以知道初始化，是從這個方法開始的。

首先入口代碼非常簡單

  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");
  }

　　

上面基本上就是整個調用流程的代碼了。第5行通過factory模式得到了一個日志工廠，第6行根據名字獲取日志logger。

第3個函數是主要的邏輯函數，根據INITIALIZATION_STATE 不同狀態，做不同的處理。

當INITIALIZATION_STATE ==0時，初始化日志框架【9行】

當INITIALIZATION_STATE ==1時，返回的TEMP_FACTORY，我們尅看下定義【15行】

static SubstituteLoggerFactory TEMP_FACTORY = new SubstituteLoggerFactory();

SubstituteLoggerFactory是什么尼，很簡單的結構，是由sl4j實現的一個。。，看一下文檔描述：

SubstituteLoggerFactory 簡單實現了ILoggerFactory接口，並總是返回一個單例的 NOPLogger實例。

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

當INITIALIZATION_STATE ==2時，返回的失敗信息【17行】，其中我們可以看下各種狀態枚舉定義，可以知道2對應的狀態是日志初始化失敗

   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;

當INITIALIZATION_STATE ==3時，返回的失敗信息【19行】，顯然是日志初始化成功，獲取日志單例信息。

當INITIALIZATION_STATE ==4時，返回的失敗信息【21行】，我們看見返回會的是NOP_FALLBACK_FACTORY（沒有找到橋接jar）對象，看下定義

 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;
  }

}

根據定義和和注釋，我們我們可以大膽猜測，4狀態就是什么都不做，NO Operator Logger Factory.僅僅是一個空實現。

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

二、核心代碼分析

重點分析這個方法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()") != -1) {
        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);
    }
  }

首先進入bind方法，

bind方法第9行，findPossibleStaticLoggerBinderPathSet（），根據名字我們知道這個函數的功能是查找可能的StaticLoggerBinder路徑集合。

  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;
  }

我們可以看到都是在加載StaticLoggerBinder.class類

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

那么StaticLoggerBinder.class是干嘛的尼？傳送門：http://skyao.github.io/2014/07/21/slfj4-binding/，后續會對StaticLoggerBinder仔細分析。

bind方法第10行，假設找到多個StaticLoggerBinder.class，就提示輸出信息。

bind方法第12行，很關鍵的一行代碼，和第10行關聯起來了。獲取一個StaticLoggerBinder單例.

 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);
    }
  }

可以看出其實就是一個單例，並初始化了。初始化的具體詳情，我們在后續會分析。這里我們只需要知道得到了一個StaticLoggerBinder單例對象即可。

bind方法14，15，16行主要是改變狀態，顯示警告信息等。

由此我們知道bind方法核心功能是加載了StaticLoggerBinder.class，並初始化了單例對象。

我們回到上面getILoggerFactory方法。

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

即StaticLoggerBinder的getLoggerFactory方法，我們看一下定義。

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();
  }

在第二行判斷initialized狀態在init()方法第20行知道，在初始化完成后，即為true。所以getLoggerFactory方法會直接到第6行。

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

第6行獲取到一個ContextSelectorStaticBinder的實例。並且獲取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);
    }
  }

我們查詢代碼知道getContextSelector獲取的對象是在init()中方法賦值的。

在StaticLoggerBinder類中init()方法第19行代碼，進行了ContextSelectorStaticBinder的實例化。

contextSelectorBinder.getContextSelector()根據代碼知道，其實就是LoggerContext包裝對象。

第10代碼，contextSelectorBinder.getContextSelector().getLoggerContext();得到一個LoggerContext對象。

即，我們的getILoggerFactory的方法，得到了一個LoggerContext對象。

在getLogger方法第二行代碼，傳遞name獲取Logger對象。

 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 = 0;
    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 == -1) {
        childName = name;
      } else {
        childName = name.substring(0, h);
      }
      // move i left of the last point
      i = h + 1;
      synchronized (logger) {
        childLogger = logger.getChildByName(childName);
        if (childLogger == null) {
          childLogger = logger.createChildByName(childName);
          loggerCache.put(childName, childLogger);
          incSize();
        }
      }
      logger = childLogger;
      if (h == -1) {
        return childLogger;
      }
    }
  }

至此，整個流程就走完了。

下一章，我們會對整個sl4j架構進行分析。分析代碼的優缺點。

-------------------------------------------------------------------------華麗分割線，下面是StaticLoggerBinder代碼分析-------------------------------

 

 

 

 

 

 

 

在我們的源碼目錄中，並沒有這個類

那么他在哪里尼？這就是實現接口反轉和適配很重要的一個環節了，還記得我們開始第一幅圖么

，

sl4j-api會調用

看下類類定StaticLoggerBinder.class：binding一個實際的ILoggerFactory的實例。

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

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();
  }

}

先看下類圖：