mybatis 日志的使用以及设计

1、为什么要配置mybtis的logger?

mybatis自己设计以及实现了org.apache.ibatis.logging.Log接口。

Mybatis为了避免对第三方的日志包存在强依赖，内部的Log采用了代理模式。通过配置的方式，代理真实的日志对象

如果没有配置log,mybatis会按照以下顺序尝试加载Log:SL4j->Common logging->log4j2->log4j->jdkLoging->noLogging

   static {
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useSlf4jLogging();
       }
     });
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useCommonsLogging();
       }
     });
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useLog4J2Logging();
       }
     });
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useLog4JLogging();
       }
     });
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useJdkLogging();
       }
     });
     tryImplementation(new Runnable() {
       @Override
       public void run() {
         useNoLogging();
       }
     });
   }

加载具体Logger的方式:

通过调用具体Logger的构造函数，反射出。

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.");
      }
      logConstructor = candidate;
    } catch (Throwable t) {
      throw new LogException("Error setting Log implementation.  Cause: " + t, t);
    }
  }