: Cannot find class: DB_VENDOR

在mybatis 中使用databaseIdProvider节点配置项（<databaseIdProvider type="DB_VENDOR">）时， 出现如下错误提示：

Exception in thread "main" : 
### Error building SqlSession.
### The error may exist in SQL Mapper Configuration
### Cause: : Error parsing SQL Mapper Configuration. Cause: : Error resolving class. Cause: : Could not resolve type alias 'DB_VENDOR'.  Cause: : Cannot find class: DB_VENDOR
	at (:23)
	at (:79)
	at (:63)
	at (:20)
Caused by: : Error parsing SQL Mapper Configuration. Cause: : Error resolving class. Cause: : Could not resolve type alias 'DB_VENDOR'.  Cause: : Cannot find class: DB_VENDOR
	at (:106)
	at (:89)
	at (:77)
	... 2 more
Caused by: : Error resolving class. Cause: : Could not resolve type alias 'DB_VENDOR'.  Cause: : Cannot find class: DB_VENDOR
	at (:100)
	at (:244)
	at (:102)
	... 4 more
Caused by: : Could not resolve type alias 'DB_VENDOR'.  Cause: : Cannot find class: DB_VENDOR
	at (:114)
	at (:127)
	at (:98)
	... 6 more
Caused by: : Cannot find class: DB_VENDOR
	at (:188)
	at (:87)
	at (:254)
	at (:110)
	... 8 more

原因是DB_VENDOR是从3.2.3版本开始使用的别名，3.2.3(不含)以前的板本不支持此名称，需要使用VENDOR。

从mybatis源代码中可以看出：

V3.2.3

package ;
public class Configuration {
  public Configuration() {
    ("JDBC", );
    ("MANAGED", );
    ("JNDI", );
    ("POOLED", );
    ("UNPOOLED", );
    ("PERPETUAL", );
    ("FIFO", );
    ("LRU", );
    ("SOFT", );
    ("WEAK", );
    ("DB_VENDOR", );
    ("XML", );
    ("RAW", );
    ("SLF4J", );
    ("COMMONS_LOGGING", );
    ("LOG4J", );
    ("LOG4J2", );
    ("JDK_LOGGING", );
    ("STDOUT_LOGGING", );
    ("NO_LOGGING", );
    ("CGLIB", );
    ("JAVASSIST", );
    ();
    ();
  }
}

而在3.2.3的xml文件初始化时，使用了VENDOR转换，可以同时支持老板本的VENDOR：

package ;
public class XMLConfigBuilder extends BaseBuilder {
  private void databaseIdProviderElement(XNode context) throws Exception {
    DatabaseIdProvider databaseIdProvider = null;
    if (context != null) {
      String type = ("type");
      if ("VENDOR".equals(type)) type = "DB_VENDOR";// awful patch to keep backward compatibility
      Properties properties = ();
      databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
      (properties);
    }
  }
}

 

而在3.2.3以前的代码中，则不支持DB_VENDOR：

V3.2.2

package ;
public class Configuration {
  public Configuration() {
    ("JDBC", );
    ("MANAGED", );
    ("JNDI", );
    ("POOLED", );
    ("UNPOOLED", );
    ("PERPETUAL", );
    ("FIFO", );
    ("LRU", );
    ("SOFT", );
    ("WEAK", 
    ("VENDOR", );
    ("XML", );
    ("RAW", );
    ("SLF4J", );
    ("COMMONS_LOGGING", );
    ("LOG4J", );
    ("JDK_LOGGING", );
    ("STDOUT_LOGGING", );
    ("NO_LOGGING", );
    
    ("CGLIB", );
    ("JAVASSIST", );
    
    ();
    ();
  }
}

 

package ;
public class XMLConfigBuilder extends BaseBuilder {
    private void databaseIdProviderElement(XNode context) throws Exception {
    DatabaseIdProvider databaseIdProvider = null;
    if (context != null) {
      String type = ("type");
      Properties properties = ();
      databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
      (properties);
    }
    Environment environment = ();
    if (environment != null && databaseIdProvider != null) {
      String databaseId = (());
      (databaseId);
    }
  }
}

因此如果在使用旧的包，而又对应使用新的文档开发时，很可能引发此问题