logger(二)、springBoot的日志源码查看(LogBack + slf4j)——创建ILoggerFactory
作者:互联网
上篇博客介绍了logback是怎么对接slf4j的,简言之,就是通过下面这行代码
slf4j委托具体实现框架的StaticLoggerBinder来返回一个ILoggerFactory,从而对接到具体实现框架上
这篇博客就接下来介绍一下,logback的StaticLoggerBinder类是怎么创建ILoggerFactory的
在图中可以看到,在logback里,ILoggerFactory的实现类是LoggerContext
logback的StaticLoggerBinder类实现了LoggerFactoryBinder接口,这个接口有两个方法
/** * An internal interface which helps the static {@link org.slf4j.LoggerFactory} * class bind with the appropriate {@link ILoggerFactory} instance. * * @author Ceki Gülcü */ public interface LoggerFactoryBinder { /** * Return the instance of {@link ILoggerFactory} that * {@link org.slf4j.LoggerFactory} class should bind to. * * @return the instance of {@link ILoggerFactory} that * {@link org.slf4j.LoggerFactory} class should bind to. */ public ILoggerFactory getLoggerFactory(); /** * The String form of the {@link ILoggerFactory} object that this * <code>LoggerFactoryBinder</code> instance is <em>intended</em> to return. * * <p>This method allows the developer to interrogate this binder's intention * which may be different from the {@link ILoggerFactory} instance it is able to * yield in practice. The discrepancy should only occur in case of errors. * * @return the class name of the intended {@link ILoggerFactory} instance */ public String getLoggerFactoryClassStr(); }
其中比较重要的是getLoggerFactory()方法,其实自定义的StaticLoggerBinder类不实现这个接口也是可以的,只要能保证提供getLoggerFactory()方法,并返回一个ILoggerFactory就可以了
下面就来具体地看看StaticLoggerBinder类的代码:
首先,该类必须有一个getSingleton()方法,来返回该类的单例
public class StaticLoggerBinder implements LoggerFactoryBinder { public static String REQUESTED_API_VERSION = "1.7.16"; static final String NULL_CS_URL = "http://logback.qos.ch/codes.html#null_CS"; private static StaticLoggerBinder SINGLETON = new StaticLoggerBinder(); private static Object KEY = new Object(); private boolean initialized = false; private LoggerContext defaultLoggerContext = new LoggerContext(); private final ContextSelectorStaticBinder contextSelectorBinder = ContextSelectorStaticBinder.getSingleton(); private StaticLoggerBinder() { this.defaultLoggerContext.setName("default"); } public static StaticLoggerBinder getSingleton() { return SINGLETON; }
以上代码用了比较简单的单例模式,提供getSingleton()方法是对接slf4j的强制要求
然后这个类用了一个static块来保证初始化
void init() { try { try { //委托ContextInitializer类对defaultLoggerContext进行初始化 (new ContextInitializer(this.defaultLoggerContext)).autoConfig(); } catch (JoranException var2) { Util.report("Failed to auto configure default logger context", var2); } if (!StatusUtil.contextHasStatusListener(this.defaultLoggerContext)) { StatusPrinter.printInCaseOfErrorsOrWarnings(this.defaultLoggerContext); } //对ContextSelectorStaticBinder类进行初始化 this.contextSelectorBinder.init(this.defaultLoggerContext, KEY); this.initialized = true; } catch (Exception var3) { Util.report("Failed to instantiate [" + LoggerContext.class.getName() + "]", var3); } } static { SINGLETON.init(); }
这个初始化方法init()里做了2件事:
第一件事是委托ContextInitializer类对defaultLoggerContext进行初始化。这里如果找到了任一配置文件,就会根据配置文件去初始化LoggerContext,如果没找到,会使用默认配置。关于LoggerContext是怎么根据配置文件进行配置的,在后面的博客中介绍,这里先略过
第二件事是对ContextSelectorStaticBinder类进行初始化
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("logback.ContextSelector"); if (contextSelectorStr == null) { this.contextSelector = new DefaultContextSelector(defaultLoggerContext); } else if (contextSelectorStr.equals("JNDI")) { this.contextSelector = new ContextJNDISelector(defaultLoggerContext); } else { this.contextSelector = dynamicalContextSelector(defaultLoggerContext, contextSelectorStr); } }
如果系统参数中配置了JNDI,这里会得到一个ContextJNDISelector,实际应用中,一般会得到一个DefaultContextSelector,并且把已经初始化完成的defaultLoggerContext传给新创建的这个DefaultContextSelector
经过上面的步骤,StaticLoggerBinder的init()方法就走完了,接下来就会调用到关键的getLoggerFactory()方法
public ILoggerFactory getLoggerFactory() { if (!this.initialized) { return this.defaultLoggerContext; } else if (this.contextSelectorBinder.getContextSelector() == null) { throw new IllegalStateException("contextSelector cannot be null. See also http://logback.qos.ch/codes.html#null_CS"); } else { return this.contextSelectorBinder.getContextSelector().getLoggerContext(); } }
可以看到,这里有2条分支,如果initialized是false,那么会直接返回defaultLoggerContext。否则就委托刚才提到的ContextSelectorStaticBinder返回一个ContextSelector(一般就是DefaultContextSelector),然后由ContextSelector来返回LoggerContext
public class DefaultContextSelector implements ContextSelector { private LoggerContext defaultLoggerContext; public DefaultContextSelector(LoggerContext context) { this.defaultLoggerContext = context; } public LoggerContext getLoggerContext() { return this.getDefaultLoggerContext(); } public LoggerContext getDefaultLoggerContext() { return this.defaultLoggerContext; } public LoggerContext detachLoggerContext(String loggerContextName) { return this.defaultLoggerContext; } public List<String> getContextNames() { return Arrays.asList(this.defaultLoggerContext.getName()); } public LoggerContext getLoggerContext(String name) { return this.defaultLoggerContext.getName().equals(name) ? this.defaultLoggerContext : null; } }
总结一下这个过程:
1、StaticLoggerBinder在加载的时候,会去读取配置文件,并根据配置文件对LoggerContext进行初始化
2、然后初始化ContextSelectorStaticBinder,在这个类内部new一个DefaultContextSelector,并把第一步中配置完毕的LoggerContext传给DefaultContextSelector
3、调用getLoggerFactory()方法,直接返回第一步中配置的LoggerContext,或者委托DefaultContextSelector类返回LoggerContext
博客来源:
由于使用的版本较高,本文稍有不同,新版本中也见到很多新的编程思想
读logback源码系列文章(二)——提供ILoggerFactory
标签:StaticLoggerBinder,springBoot,LoggerContext,slf4j,源码,defaultLoggerContext,return 来源: https://www.cnblogs.com/lzghyh/p/14904904.html