Log日志框架的学习二.slf4j源代码分析

Commons-log + log4j 这黄金搭档一直以来都让我们很省心，很好的完成了日志的需求。但是随着技术的变更和对性能的追求，slf4j 和 logback 这对后起之秀的到来好像打破了原本很平静的日志系统，频繁的出现包冲突... 

       和平的日子不在了，让我们一起来看看究竟发生了什么...

 

 

首先看看这些个包，特别是slf4j引入后就引入了一大堆包之后就有点懵了。

为什么commons-logging和jcl-over-slf4j会有冲突呢？看一下它们的类结构

很清晰的可以看到jcl-over-slf4j 重写了 commons-logging...

 

还有slf4j-api的实现呢，同样看类：

其实就这么简单，往往看了代码之后才发现错误是这么显而易见。。。

 

 

顺着研究，继续看一下slf4j的源码及流程

1.测试类

 

package com.taobao.wuzhong.log;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * DESC:
 *
 * Copyright: Copyright 2011 m.taobao.com
 *
 * @author [e-mail]
 * @time 2011-4-6 下午03:42:11
 * @version 1.0
 **/
public class LogTest {

    // Logback tries to find a file called logback.groovy in the classpath.
    // If no such file is found, logback tries to find a file called
    // logback-test.xml in the classpath.
    // If no such file is found, it checks for the file logback.xml in the
    // classpath..
    // If neither file is found, logback configures itself automatically using
    // the BasicConfigurator which will cause logging output to be directed to
    // the console.
    @Test
    public void test() {
                //commons-logging的方式获取
        Log log = LogFactory.getLog(LogTest.class);
                //slf4j直接的方式获取，推荐用这个
        Logger log2 = LoggerFactory.getLogger(LogTest.class);
        log.debug("eeeeee {} {} {}");
        log2.debug("{} {} {}", new String[] { "a", "b", "c" });
    }

}

 

 

logFactory.getLog 会调用内部静态变量 Slf4jLogFactory.getInstance方法，如下：

 

 public Log getInstance(String name) throws LogConfigurationException {

Log instance = null;
// protect against concurrent access of loggerMap
synchronized (this) {
  instance = (Log) loggerMap.get(name);
  if (instance == null) {
    Logger logger = LoggerFactory.getLogger(name);   //slf4j的方式，代理过去了
    if(logger instanceof LocationAwareLogger) {
      instance = new SLF4JLocationAwareLog((LocationAwareLogger) logger);  //包装了一层，做适配
    } else {
      instance = new SLF4JLog(logger);
    }
    loggerMap.put(name, instance);
  }
}
return (instance);

 

loggerFactory 会调用getILoggerFactory().getlOgger()

 

LoggerFactory.java
 public static ILoggerFactory getILoggerFactory() {
    if (INITIALIZATION_STATE == UNINITIALIZED) {
      INITIALIZATION_STATE = ONGOING_INITILIZATION;
      performInitialization();

    }
    switch (INITIALIZATION_STATE) {
    case SUCCESSFUL_INITILIZATION:
      return getSingleton().getLoggerFactory();
    case FAILED_INITILIZATION:
      throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
    case ONGOING_INITILIZATION:
      // support re-entrant behavior.
      // See also http://bugzilla.slf4j.org/show_bug.cgi?id=106
      return TEMP_FACTORY;
    }
    throw new IllegalStateException("Unreachable code");
  }

 private final static void performInitialization() {
    bind();
    versionSanityCheck();
    singleImplementationSanityCheck();

  }

这里的bind很关键，这里动态的绑定了slf4j-api的实现机制

 

static {
    SINGLETON.init();
  }

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

 

获取配置信息初始化

 

autoConfig ….
public URL findURLOfDefaultConfigurationFile(boolean updateStatus) {
    ClassLoader myClassLoader = Loader.getClassLoaderOfObject(this);
    URL url = findConfigFileURLFromSystemProperties(myClassLoader, updateStatus);
    if (url != null) {
      return url;
    }

    url = Loader.getResource(TEST_AUTOCONFIG_FILE, myClassLoader);
    if (updateStatus) {
      statusOnResourceSearch(TEST_AUTOCONFIG_FILE, myClassLoader, url);
    }
    if (url != null) {
      return url;
    }

    url = Loader.getResource(AUTOCONFIG_FILE, myClassLoader);
    if (updateStatus) {
      statusOnResourceSearch(AUTOCONFIG_FILE, myClassLoader, url);
    }
    return url;
  }

  public void autoConfig() throws JoranException {
    StatusListenerConfigHelper.installIfAsked(loggerContext);
    URL url = findURLOfDefaultConfigurationFile(true);
    if (url != null) {
      configureByResource(url);
    } else {
      BasicConfigurator.configure(loggerContext);
    }
  }

 

最后画张流程图总结下，^_^

 

 

总结： log框架应该很好的诠释了 facade ， adapter ， 实现上还是比较简单的，很好的做到了接口和实现的分离，对今后的代码组织有一定的启发