ibatis 2.3x logging 加载机制， 输出sqlmap jdbc日志信息

ibatis  支持三种日志框架输出jdbc logging，加载顺序如下：

public class LogFactory {

  private static Constructor logConstructor;

  static {
    tryImplementation("org.apache.commons.logging.LogFactory", "com.ibatis.common.logging.jakarta.JakartaCommonsLoggingImpl");
    tryImplementation("org.apache.log4j.Logger", "com.ibatis.common.logging.log4j.Log4jImpl");
    tryImplementation("java.util.logging.Logger", "com.ibatis.common.logging.jdk14.Jdk14LoggingImpl");
    tryImplementation("java.lang.Object", "com.ibatis.common.logging.nologging.NoLoggingImpl");//No logging 什么都不输出，等于没有
  }

  private static void tryImplementation(String testClassName, String implClassName) {
    if (logConstructor == null) {
      try {
        Resources.classForName(testClassName);
        Class implClass = Resources.classForName(implClassName);
        logConstructor = implClass.getConstructor(new Class[]{Class.class});
      } catch (Throwable t) {
      }
    }
  }
...
}