slf4j + Logback详解

Log4j初始化详解：http://donald-draper.iteye.com/blog/2332385
Log4j日志输出详解：http://donald-draper.iteye.com/admin/blogs/2332395
slf4j +  Log4j的使用：http://donald-draper.iteye.com/admin/blogs/2332407
slf4j + Log4j 详解：http://donald-draper.iteye.com/admin/blogs/2332417
使用logback轻松管理日志 http://blog.csdn.net/mydeman/article/details/6716925
Logback日志使用详解：http://www.cnblogs.com/davidwang456/p/4448011.html
logback的介绍-配置：http://sunney2010.iteye.com/blog/1404723
slf4j +  Logback的使用：http://donald-draper.iteye.com/admin/blogs/2332438
上一篇讲了slf4j + Logback的使用，其中获取Logger的一句为
[url]private static Logger log = LoggerFactory.getLogger(testLogback.class);[/url]
下面来看这一句的具体含义：

public final class LoggerFactory
{
    static final String CODES_PREFIX = "http://www.slf4j.org/codes.html";
    static final String NO_STATICLOGGERBINDER_URL = "http://www.slf4j.org/codes.html#StaticLoggerBinder";
    static final String MULTIPLE_BINDINGS_URL = "http://www.slf4j.org/codes.html#multiple_bindings";
    static final String NULL_LF_URL = "http://www.slf4j.org/codes.html#null_LF";
    static final String VERSION_MISMATCH = "http://www.slf4j.org/codes.html#version_mismatch";
    static final String SUBSTITUTE_LOGGER_URL = "http://www.slf4j.org/codes.html#substituteLogger";
    static final String LOGGER_NAME_MISMATCH_URL = "http://www.slf4j.org/codes.html#loggerNameMismatch";
    static final String UNSUCCESSFUL_INIT_URL = "http://www.slf4j.org/codes.html#unsuccessfulInit";
    static final String UNSUCCESSFUL_INIT_MSG = "org.slf4j.LoggerFactory could not be successfully initialized. See also http://www.slf4j.org/codes.html#unsuccessfulInit";
    static final int UNINITIALIZED = 0;
    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;
    static int INITIALIZATION_STATE = 0;
    static SubstituteLoggerFactory TEMP_FACTORY = new SubstituteLoggerFactory();
    static NOPLoggerFactory NOP_FALLBACK_FACTORY = new NOPLoggerFactory();
    static final String DETECT_LOGGER_NAME_MISMATCH_PROPERTY = "slf4j.detectLoggerNameMismatch";
    static boolean DETECT_LOGGER_NAME_MISMATCH = Boolean.getBoolean("slf4j.detectLoggerNameMismatch");
    private static final String API_COMPATIBILITY_LIST[] = {
        "1.6", "1.7"
    };
    private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class";
   //根据class，获取Logger
public static Logger getLogger(Class clazz)
    {
        Logger logger = getLogger(clazz.getName());
        if(DETECT_LOGGER_NAME_MISMATCH)
        {
            Class autoComputedCallingClass = Util.getCallingClass();
            if(nonMatchingClasses(clazz, autoComputedCallingClass))
            {
                Util.report(String.format("Detected logger name mismatch. Given name: \"%s\"; computed name: \"%s\".", new Object[] {
                    logger.getName(), autoComputedCallingClass.getName()
                }));
                Util.report("See http://www.slf4j.org/codes.html#loggerNameMismatch for an explanation");
            }
        }
        return logger;
    }
    //根据class name 获取Logger
     public static Logger getLogger(String name)
    {
        //获取LoggerFactory
        ILoggerFactory iLoggerFactory = getILoggerFactory();
	//从LoggerFactory获取Logger
        return iLoggerFactory.getLogger(name);
    }
    //获取LoggerFactory
     public static ILoggerFactory getILoggerFactory()
    {
        if(INITIALIZATION_STATE == 0)
        {
            INITIALIZATION_STATE = 1;
	    //执行初始化
            performInitialization();
        }
        switch(INITIALIZATION_STATE)
        {
        case 3: // '\003'
	    //返回Log4jLoggerFactory
            return StaticLoggerBinder.getSingleton().getLoggerFactory();

        case 4: // '\004'
	//如果状态为4，则返回NOPLoggerFactory
            return NOP_FALLBACK_FACTORY;

        case 2: // '\002'
            throw new IllegalStateException("org.slf4j.LoggerFactory could not be successfully initialized. See also http://www.slf4j.org/codes.html#unsuccessfulInit");
        //如果初始化状态为1，返回临时LoggerFactory，SubstituteLoggerFactory
        case 1: // '\001'
            return TEMP_FACTORY;
        }
        throw new IllegalStateException("Unreachable code");
    }
    //执行初始化
     private static final void performInitialization()
    {
        //绑定日志工场
        bind();
        if(INITIALIZATION_STATE == 3)
	    //验证配置
            versionSanityCheck();
    }
    //绑定日志工场
     private static final void bind()
    {
        try
        {
	    //获取具体LoggerBinder类，默认为StaticLoggerBinder，在slf4j-log4j12-1.7.9.jar 中
            Set staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
            reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
            StaticLoggerBinder.getSingleton();
            INITIALIZATION_STATE = 3;
            reportActualBinding(staticLoggerBinderPathSet);
	    //从SubstituteLoggerFactory获取具体sfl4j的Logger实现，并用SubstituteLogger代理类去包装
            fixSubstitutedLoggers();
        }
	catch(NoClassDefFoundError ncde)
        {
            String msg = ncde.getMessage();
            if(messageContainsOrgSlf4jImplStaticLoggerBinder(msg))
            {
	        //初始化状态为4，返回NOPLoggerFactory,无配置Logger
                INITIALIZATION_STATE = 4;
                Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
                Util.report("Defaulting to no-operation (NOP) logger implementation");
                Util.report("See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.");
            } else
            {
                failedBinding(ncde);
                throw ncde;
            }
        }
        catch(NoSuchMethodError nsme)
        {
            String msg = nsme.getMessage();
            if(msg != null && msg.indexOf("org.slf4j.impl.StaticLoggerBinder.getSingleton()") != -1)
            {
	        //org.slf4j.LoggerFactory could not be successfully initialized
                INITIALIZATION_STATE = 2;
                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);
        }

    }
    //获取StaticLoggerBinderPathS
    private static Set findPossibleStaticLoggerBinderPathSet()
    {
        Set staticLoggerBinderPathSet = new LinkedHashSet();
        try
        {
            ClassLoader loggerFactoryClassLoader = org/slf4j/LoggerFactory.getClassLoader();
            Enumeration paths;
            if(loggerFactoryClassLoader == null)
                paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
            else
	        // private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class";
                paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
            URL path;
            for(; paths.hasMoreElements(); staticLoggerBinderPathSet.add(path))
                path = (URL)paths.nextElement();

        }
        return staticLoggerBinderPathSet;
    }
    //report多bind
    private static void reportMultipleBindingAmbiguity(Set staticLoggerBinderPathSet)
    {
        if(isAmbiguousStaticLoggerBinderPathSet(staticLoggerBinderPathSet))
        {
            Util.report("Class path contains multiple SLF4J bindings.");
            URL path;
            for(Iterator iterator = staticLoggerBinderPathSet.iterator(); iterator.hasNext(); Util.report((new StringBuilder()).append("Found binding in [").append(path).append("]").toString()))
                path = (URL)iterator.next();

            Util.report("See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.");
        }
    }
   //report实际绑定
    private static void reportActualBinding(Set staticLoggerBinderPathSet)
    {
        if(isAmbiguousStaticLoggerBinderPathSet(staticLoggerBinderPathSet))
            Util.report((new StringBuilder()).append("Actual binding is of type [").append(StaticLoggerBinder.getSingleton().getLoggerFactoryClassStr()).append("]").toString());
    }
    //从SubstituteLoggerFactory获取具体sfl4j的Logger实现，并用SubstituteLogger代理类去包装
    //如果日志Logger为sfl4j的Logger的实现，则用SubstituteLogger去代理具体的实现Logger
    private static final void fixSubstitutedLoggers()
    {
       //从临时工厂SubstituteLoggerFactory，获取所有Loggers
        List loggers = TEMP_FACTORY.getLoggers();
        if(loggers.isEmpty())
            return;
        Util.report("The following set of substitute loggers may have been accessed");
        Util.report("during the initialization phase. Logging calls during this");
        Util.report("phase were not honored. However, subsequent logging calls to these");
        Util.report("loggers will work as normally expected.");
        Util.report("See also http://www.slf4j.org/codes.html#substituteLogger");
        SubstituteLogger subLogger;
        for(Iterator i$ = loggers.iterator(); i$.hasNext(); Util.report(subLogger.getName()))
        {
            subLogger = (SubstituteLogger)i$.next();
            subLogger.setDelegate(getLogger(subLogger.getName()));
        }

        TEMP_FACTORY.clear();
    }
    //验证配置，校验文件
    private static final void versionSanityCheck()
    {
        try
        {
            String requested = StaticLoggerBinder.REQUESTED_API_VERSION;
            boolean match = false;
            for(int i = 0; i < API_COMPATIBILITY_LIST.length; i++)
                if(requested.startsWith(API_COMPATIBILITY_LIST[i]))
                    match = true;

            if(!match)
            {
                Util.report((new StringBuilder()).append("The requested version ").append(requested).append(" by your slf4j binding is not compatible with ").append(Arrays.asList(API_COMPATIBILITY_LIST).toString()).toString());
                Util.report("See http://www.slf4j.org/codes.html#version_mismatch for further details.");
            }
        }
    }
}

//StaticLoggerBinder

public class StaticLoggerBinder
    implements LoggerFactoryBinder
{
    public static String REQUESTED_API_VERSION = "1.6";
    static final String NULL_CS_URL = "http://logback.qos.ch/codes.html#null_CS";
    private static StaticLoggerBinder SINGLETON;
    private static Object KEY = new Object();
    private boolean initialized;
    private LoggerContext defaultLoggerContext;
    private final ContextSelectorStaticBinder contextSelectorBinder = ContextSelectorStaticBinder.getSingleton();

    static 
    {
        SINGLETON = new StaticLoggerBinder();
	//初始化
        SINGLETON.init();
    }
   private StaticLoggerBinder()
    {
        initialized = false;
        defaultLoggerContext = new LoggerContext();
        defaultLoggerContext.setName("default");
    }

    public static StaticLoggerBinder getSingleton()
    {
        return SINGLETON;
    }
    //初始化
     void init()
    {
        try
        {
            try
            {
	        //配置defaultLoggerContext
                (new ContextInitializer(defaultLoggerContext)).autoConfig();
            }
            catch(JoranException je)
            {
                Util.report("Failed to auto configure default logger context", je);
            }
            StatusPrinter.printInCaseOfErrorsOrWarnings(defaultLoggerContext);
            contextSelectorBinder.init(defaultLoggerContext, KEY);
            initialized = true;
        }
        catch(Throwable t)
        {
            Util.report((new StringBuilder()).append("Failed to instantiate [").append(ch/qos/logback/classic/LoggerContext.getName()).append("]").toString(), t);
        }
    }
}

//ContextInitializer

public class ContextInitializer
{
    public static final String GROOVY_AUTOCONFIG_FILE = "logback.groovy";
    public static final String AUTOCONFIG_FILE = "logback.xml";
    public static final String TEST_AUTOCONFIG_FILE = "logback-test.xml";
    public static final String CONFIG_FILE_PROPERTY = "logback.configurationFile";
    public static final String STATUS_LISTENER_CLASS = "logback.statusListenerClass";
    public static final String SYSOUT = "SYSOUT";
    final LoggerContext loggerContext;
    public ContextInitializer(LoggerContext loggerContext)
    {
        this.loggerContext = loggerContext;
    }
     public void autoConfig()
        throws JoranException
    {
        StatusListenerConfigHelper.installIfAsked(loggerContext);
	//获取配置资源，先找logback.groovy，logback-test.xml，logback.xml
        URL url = findURLOfDefaultConfigurationFile(true);
        if(url != null)
	    //根据资源配置LogContext
            configureByResource(url);
        else
            BasicConfigurator.configure(loggerContext);
    }
    //获取配置资源，先找logback.groovy，logback-test.xml，logback.xml
    public URL findURLOfDefaultConfigurationFile(boolean updateStatus)
    {
        ClassLoader myClassLoader = Loader.getClassLoaderOfObject(this);
        URL url = findConfigFileURLFromSystemProperties(myClassLoader, updateStatus);
        if(url != null)
            return url;
        url = getResource("logback.groovy", myClassLoader, updateStatus);
        if(url != null)
            return url;
        url = getResource("logback-test.xml", myClassLoader, updateStatus);
        if(url != null)
            return url;
        else
            return getResource("logback.xml", myClassLoader, updateStatus);
    }
    //根据资源配置LogContext
    public void configureByResource(URL url)
        throws JoranException
    {
        if(url == null)
            throw new IllegalArgumentException("URL argument cannot be null");
        if(url.toString().endsWith("groovy"))
            if(EnvUtil.isGroovyAvailable())
            {
                GafferUtil.runGafferConfiguratorOn(loggerContext, this, url);
            } else
            {
                StatusManager sm = loggerContext.getStatusManager();
                sm.add(new ErrorStatus("Groovy classes are not available on the class path. ABORTING INITIALIZATION.", loggerContext));
            }
        if(url.toString().endsWith("xml"))
        {
            JoranConfigurator configurator = new JoranConfigurator();
	    //设置LogContext
            configurator.setContext(loggerContext);
	    //根据资源配置LogContext
            configurator.doConfigure(url);
        }
    }
}

//JoranConfigurator

public class JoranConfigurator extends JoranConfiguratorBase
{
    public void addInstanceRules(RuleStore rs)
    {
        super.addInstanceRules(rs);
        rs.addRule(new Pattern("configuration"), new ConfigurationAction());
        rs.addRule(new Pattern("configuration/contextName"), new ContextNameAction());
        rs.addRule(new Pattern("configuration/contextListener"), new LoggerContextListenerAction());
        rs.addRule(new Pattern("configuration/insertFromJNDI"), new InsertFromJNDIAction());
        rs.addRule(new Pattern("configuration/evaluator"), new EvaluatorAction());
        rs.addRule(new Pattern("configuration/appender/sift"), new SiftAction());
        rs.addRule(new Pattern("configuration/appender/sift/*"), new NOPAction());
        rs.addRule(new Pattern("configuration/logger"), new LoggerAction());
        rs.addRule(new Pattern("configuration/logger/level"), new LevelAction());
        rs.addRule(new Pattern("configuration/root"), new RootLoggerAction());
        rs.addRule(new Pattern("configuration/root/level"), new LevelAction());
        rs.addRule(new Pattern("configuration/logger/appender-ref"), new AppenderRefAction());
        rs.addRule(new Pattern("configuration/root/appender-ref"), new AppenderRefAction());
        rs.addRule(new Pattern("*/if"), new IfAction());
        rs.addRule(new Pattern("*/if/then"), new ThenAction());
        rs.addRule(new Pattern("*/if/then/*"), new NOPAction());
        rs.addRule(new Pattern("*/if/else"), new ElseAction());
        rs.addRule(new Pattern("*/if/else/*"), new NOPAction());
        if(PlatformInfo.hasJMXObjectName())
            rs.addRule(new Pattern("configuration/jmxConfigurator"), new JMXConfiguratorAction());
        rs.addRule(new Pattern("configuration/include"), new IncludeAction());
        rs.addRule(new Pattern("configuration/consolePlugin"), new ConsolePluginAction());
    }
    protected void addDefaultNestedComponentRegistryRules(DefaultNestedComponentRegistry registry)
    {
        DefaultNestedComponentRules.addDefaultNestedComponentRegistryRules(registry);
    }
}

//JoranConfiguratorBase

public abstract class JoranConfiguratorBase extends GenericConfigurator

//GenericConfigurator

public abstract class GenericConfigurator extends ContextAwareBase
{ 
//根据资源配置LogContext
public final void doConfigure(URL url)
        throws JoranException
    {
        try
        {
	    //设置LogContext的URL
            informContextOfURLUsedForConfiguration(url);
            URLConnection urlConnection = url.openConnection();
            urlConnection.setUseCaches(false);
            InputStream in = urlConnection.getInputStream();
	    //根据输入流，配置LogContext
            doConfigure(in);
            in.close();
        }
        catch(IOException ioe)
        {
            String errMsg = (new StringBuilder()).append("Could not open URL [").append(url).append("].").toString();
            addError(errMsg, ioe);
            throw new JoranException(errMsg, ioe);
        }
    }
    //设置LogContext的URL
      protected void informContextOfURLUsedForConfiguration(URL url)
    {
        getContext().putObject(CoreConstants.URL_OF_LAST_CONFIGURATION_VIA_JORAN, url);
    }
    public final void doConfigure(InputStream inputStream)
        throws JoranException
    {
        doConfigure(new InputSource(inputStream));
    }
    //根据输入流源，配置LogContext
    public final void doConfigure(InputSource inputSource)
        throws JoranException
    {
        SaxEventRecorder recorder = new SaxEventRecorder();
        recorder.setContext(context);
        recorder.recordEvents(inputSource);
        buildInterpreter();
        synchronized(context.getConfigurationLock())
        {
            interpreter.play(recorder.saxEventList);
        }
    }
     protected Interpreter interpreter;
}

//LoggerContext

public class LoggerContext extends ContextBase
    implements ILoggerFactory, LifeCycle
{

    public LoggerContext()
    {
        noAppenderWarning = 0;
        packagingDataEnabled = true;
        maxCallerDataDepth = 8;
        started = false;
        resetCount = 0;
        loggerCache = new Hashtable();
        loggerContextRemoteView = new LoggerContextVO(this);
        root.setLevel(Level.DEBUG);
        loggerCache.put("ROOT", root);
        initEvaluatorMap();
        size = 1;
    }
    //获取Logger，ch.qos.logback.classic.Logger
    public volatile Logger getLogger(String x0)
    {
        return getLogger(x0);
    }
    final ch.qos.logback.classic.Logger root = new ch.qos.logback.classic.Logger("ROOT", null, this);
    private int size;
    private int noAppenderWarning;
    private final List loggerContextListenerList = new ArrayList();
    private Hashtable loggerCache;
    private LoggerContextVO loggerContextRemoteView;
    private final TurboFilterList turboFilterList = new TurboFilterList();
    private boolean packagingDataEnabled;
    private int maxCallerDataDepth;
    boolean started;
    int resetCount;
}

//ch.qos.logback.classic.Logger

public final class Logger
    implements org.slf4j.Logger, LocationAwareLogger, AppenderAttachable, Serializable
{
 Logger(String name, Logger parent, LoggerContext loggerContext)
    {
        additive = true;
        this.name = name;
        this.parent = parent;
        this.loggerContext = loggerContext;
        buildRemoteView();
        instanceCount++;
    }

    public final Level getEffectiveLevel()
    {
        return Level.toLevel(effectiveLevelInt);
    }
    //产生Info日志
    public void info(String msg)
    {
        filterAndLog_0_Or3Plus(FQCN, null, Level.INFO, msg, null, null);
    }
    private final void filterAndLog_0_Or3Plus(String localFQCN, Marker marker, Level level, String msg, Object params[], Throwable t)
    {
        FilterReply decision = loggerContext.getTurboFilterChainDecision_0_3OrMore(marker, this, level, msg, params, t);
        if(decision == FilterReply.NEUTRAL)
        {
            if(effectiveLevelInt > level.levelInt)
                return;
        } else
        if(decision == FilterReply.DENY)
            return;
        buildLoggingEventAndAppend(localFQCN, marker, level, msg, params, t);
    }
}

//如果无配置文件，则使用BasicConfigurator，简单的控制台输出

public class BasicConfigurator
{
    public static void configure(LoggerContext lc)
    {
        StatusManager sm = lc.getStatusManager();
        if(sm != null)
            sm.add(new InfoStatus("Setting up default configuration.", lc));
        ConsoleAppender ca = new ConsoleAppender();
        ca.setContext(lc);
        ca.setName("console");
        PatternLayoutEncoder pl = new PatternLayoutEncoder();
        pl.setContext(lc);
        pl.setPattern("%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n");
        pl.start();
        ca.setEncoder(pl);
        ca.start();
        Logger rootLogger = lc.getLogger("ROOT");
        rootLogger.addAppender(ca);
    }
    public static void configureDefaultContext()
    {
        LoggerContext lc = (LoggerContext)LoggerFactory.getILoggerFactory();
        configure(lc);
    }

    static final BasicConfigurator hiddenSingleton = new BasicConfigurator();

}

总结：
从上面可以看出logback与sfl4j的整合，实际上是通过实现类StaticLoggerBinder，LoggerFactory加载
StaticLoggerBinder，StaticLoggerBinder通过静态语句块来，初始化LoggerContext，而LoggerContext实现
的ILoggerFactory接口，从LoggerContext获取的Logger实际为ch.qos.logback.classic.Logger，
即org.slf4j.Logger的实现类。