mybatis 架构及基础模块

// getLog(Class<?> aClass)方法 
  public static Log getLog(Class<?> aClass) {
    return getLog(aClass.getName());
  }
//通过类构造器实例化实例
  public static Log getLog(String logger) {
    try {
      return logConstructor.newInstance(logger);
    } catch (Throwable t) {
      //如果出现异常，抛出异常，由外层处理
      throw new LogException("Error creating logger for logger " + logger + ".  Cause: " + t, t);
    }
  }

public final class LogFactory {

  /**
   * Marker to be used by logging implementations that support markers.
   */
  public static final String MARKER = "MYBATIS";
//具体日志实现类的构造器
  private static Constructor<? extends Log> logConstructor;
//按顺序加载
  static {
    tryImplementation(LogFactory::useSlf4jLogging);
    tryImplementation(LogFactory::useCommonsLogging);
    tryImplementation(LogFactory::useLog4J2Logging);
    tryImplementation(LogFactory::useLog4JLogging);
    tryImplementation(LogFactory::useJdkLogging);
    tryImplementation(LogFactory::useNoLogging);
  }

//启动一个线程获取日志实现类的构造器，并设置构造器的值
  private static void tryImplementation(Runnable runnable) {
    if (logConstructor == null) {
      try {
        runnable.run();
      } catch (Throwable t) {
        //捕捉到异常不进行处理
        // ignore
      }
    }
  }

//加载具体的日志实现
  public static synchronized void useSlf4jLogging() {
    setImplementation(org.apache.ibatis.logging.slf4j.Slf4jImpl.class);
  }

  //拿到类构造器，并给类的logConstructor变量赋值，后期getLog()方法将使用logConstructor实例一个日志类实例。
  private static void setImplementation(Class<? extends Log> implClass) {
    try {
      Constructor<? extends Log> candidate = implClass.getConstructor(String.class);
      Log log = candidate.newInstance(LogFactory.class.getName());
      if (log.isDebugEnabled()) {
        log.debug("Logging initialized using ‘" + implClass + "‘ adapter.");
      }
      //赋值
      logConstructor = candidate;
    } catch (Throwable t) {
      throw new LogException("Error setting Log implementation.  Cause: " + t, t);
    }
  }

/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.logging.slf4j;

import org.apache.ibatis.logging.Log;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
import org.slf4j.spi.LocationAwareLogger;

/**
 * @author Clinton Begin
 * @author Eduardo Macarron
 */
//实现Log 接口，通过slf4j具体实现完成适配
public class Slf4jImpl implements Log {

  private Log log;

  public Slf4jImpl(String clazz) {
    Logger logger = LoggerFactory.getLogger(clazz);

    if (logger instanceof LocationAwareLogger) {
      try {
        // check for slf4j >= 1.6 method signature
        logger.getClass().getMethod("log", Marker.class, String.class, int.class, String.class, Object[].class, Throwable.class);
        log = new Slf4jLocationAwareLoggerImpl((LocationAwareLogger) logger);
        return;
      } catch (SecurityException | NoSuchMethodException e) {
        // fail-back to Slf4jLoggerImpl
      }
    }

    // Logger is not LocationAwareLogger or slf4j version < 1.6
    log = new Slf4jLoggerImpl(logger);
  }

  @Override
  public boolean isDebugEnabled() {
    return log.isDebugEnabled();
  }

  @Override
  public boolean isTraceEnabled() {
    return log.isTraceEnabled();
  }
  
  @Override
  public void error(String s, Throwable e) {
    log.error(s, e);
  }

  @Override
  public void error(String s) {
    log.error(s);
  }

  @Override
  public void debug(String s) {
    log.debug(s);
  }

  @Override
  public void trace(String s) {
    log.trace(s);
  }

  @Override
  public void warn(String s) {
    log.warn(s);
  }

}

/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.logging;

/**
 * @author Clinton Begin
 */
public interface Log {

  boolean isDebugEnabled();

  boolean isTraceEnabled();

  void error(String s, Throwable e);

  void error(String s);

  void debug(String s);

  void trace(String s);

  void warn(String s);

}

/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.logging.log4j;

import org.apache.ibatis.logging.Log;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;

/**
 * @author Eduardo Macarron
 */
public class Log4jImpl implements Log {

  private static final String FQCN = Log4jImpl.class.getName();

  private final Logger log;

  public Log4jImpl(String clazz) {
    log = Logger.getLogger(clazz);
  }

  @Override
  public boolean isDebugEnabled() {
    return log.isDebugEnabled();
  }

  @Override
  public boolean isTraceEnabled() {
    return log.isTraceEnabled();
  }

  @Override
  public void error(String s, Throwable e) {
    log.log(FQCN, Level.ERROR, s, e);
  }

  @Override
  public void error(String s) {
    log.log(FQCN, Level.ERROR, s, null);
  }

  @Override
  public void debug(String s) {
    log.log(FQCN, Level.DEBUG, s, null);
  }

  @Override
  public void trace(String s) {
    log.log(FQCN, Level.TRACE, s, null);
  }

  @Override
  public void warn(String s) {
    log.log(FQCN, Level.WARN, s, null);
  }

}

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j;

import org.apache.log4j.spi.LoggerFactory;


/**
  This is the central class in the log4j package. Most logging
  operations, except configuration, are done through this class.

  @since log4j 1.2

  @author Ceki Gülcü */
public class Logger extends Category {

  /**
     The fully qualified name of the Logger class. See also the
     getFQCN method. */
  private static final String FQCN = Logger.class.getName();


  protected
  Logger(String name) {
    super(name);
  }

  /**
    Log a message object with the {@link Level#FINE FINE} level which
    is just an alias for the {@link Level#DEBUG DEBUG} level.

    <p>This method first checks if this category is <code>DEBUG</code>
    enabled by comparing the level of this category with the {@link
    Level#DEBUG DEBUG} level. If this category is
    <code>DEBUG</code> enabled, then it converts the message object
    (passed as parameter) to a string by invoking the appropriate
    {@link org.apache.log4j.or.ObjectRenderer}. It then proceeds to call all the
    registered appenders in this category and also higher in the
    hierarchy depending on the value of the additivity flag.

    <p><b>WARNING</b> Note that passing a {@link Throwable} to this
    method will print the name of the <code>Throwable</code> but no
    stack trace. To print a stack trace use the {@link #debug(Object,
    Throwable)} form instead.

    @param message the message object to log. */
  //public
  //void fine(Object message) {
  //  if(repository.isDisabled(Level.DEBUG_INT))
  //    return;
  //  if(Level.DEBUG.isGreaterOrEqual(this.getChainedLevel())) {
  //    forcedLog(FQCN, Level.DEBUG, message, null);
  //  }
  //}


  /**
   Log a message object with the <code>FINE</code> level including
   the stack trace of the {@link Throwable} <code>t</code> passed as
   parameter.

   <p>See {@link #fine(Object)} form for more detailed information.

   @param message the message object to log.
   @param t the exception to log, including its stack trace.  */
  //public
  //void fine(Object message, Throwable t) {
  //  if(repository.isDisabled(Level.DEBUG_INT))
  //    return;
  //  if(Level.DEBUG.isGreaterOrEqual(this.getChainedLevel()))
  //    forcedLog(FQCN, Level.FINE, message, t);
  //}

  /**
   * Retrieve a logger named according to the value of the
   * <code>name</code> parameter. If the named logger already exists,
   * then the existing instance will be returned. Otherwise, a new
   * instance is created.  
   *
   * <p>By default, loggers do not have a set level but inherit it
   * from their neareast ancestor with a set level. This is one of the
   * central features of log4j.
   *
   * @param name The name of the logger to retrieve.  
  */
  static
  public
  Logger getLogger(String name) {
    return LogManager.getLogger(name);
  }

  /**
   * Shorthand for <code>getLogger(clazz.getName())</code>.
   *
   * @param clazz The name of <code>clazz</code> will be used as the
   * name of the logger to retrieve.  See {@link #getLogger(String)}
   * for more detailed information.
   */
  static
  public
  Logger getLogger(Class clazz) {
    return LogManager.getLogger(clazz.getName());
  }


  /**
   * Return the root logger for the current logger repository.
   * <p>
   * The {@link #getName Logger.getName()} method for the root logger always returns
   * string value: "root". However, calling
   * <code>Logger.getLogger("root")</code> does not retrieve the root
   * logger but a logger just under root named "root".
   * <p>
   * In other words, calling this method is the only way to retrieve the 
   * root logger.
   */
  public
  static
  Logger getRootLogger() {
    return LogManager.getRootLogger();
  }

  /**
     Like {@link #getLogger(String)} except that the type of logger
     instantiated depends on the type returned by the {@link
     LoggerFactory#makeNewLoggerInstance} method of the
     <code>factory</code> parameter.

     <p>This method is intended to be used by sub-classes.

     @param name The name of the logger to retrieve.

     @param factory A {@link LoggerFactory} implementation that will
     actually create a new Instance.

     @since 0.8.5 */
  public
  static
  Logger getLogger(String name, LoggerFactory factory) {
    return LogManager.getLogger(name, factory);
  }

    /**
     * Log a message object with the {@link org.apache.log4j.Level#TRACE TRACE} level.
     *
     * @param message the message object to log.
     * @see #debug(Object) for an explanation of the logic applied.
     * @since 1.2.12
     */
    public void trace(Object message) {
      if (repository.isDisabled(Level.TRACE_INT)) {
        return;
      }

      if (Level.TRACE.isGreaterOrEqual(this.getEffectiveLevel())) {
        forcedLog(FQCN, Level.TRACE, message, null);
      }
    }

    /**
     * Log a message object with the <code>TRACE</code> level including the
     * stack trace of the {@link Throwable}<code>t</code> passed as parameter.
     *
     * <p>
     * See {@link #debug(Object)} form for more detailed information.
     * </p>
     *
     * @param message the message object to log.
     * @param t the exception to log, including its stack trace.
     * @since 1.2.12
     */
    public void trace(Object message, Throwable t) {
      if (repository.isDisabled(Level.TRACE_INT)) {
        return;
      }

      if (Level.TRACE.isGreaterOrEqual(this.getEffectiveLevel())) {
        forcedLog(FQCN, Level.TRACE, message, t);
      }
    }

    /**
     * Check whether this category is enabled for the TRACE  Level.
     * @since 1.2.12
     *
     * @return boolean - <code>true</code> if this category is enabled for level
     *         TRACE, <code>false</code> otherwise.
     */
    public boolean isTraceEnabled() {
        if (repository.isDisabled(Level.TRACE_INT)) {
            return false;
          }

          return Level.TRACE.isGreaterOrEqual(this.getEffectiveLevel());
    }

}