MyBatis: mybatisConfig.xml configuration file

The content and order of the configuration in mybatisConfig.xml are as follows:

• properties
• settings (global configuration parameters)
• typeAliases (type aliases)
• typeHandlers (type processors)
• objectFactory
• plugins
• environments (environment collection attribute object)
  • environment (environment sub-attribute object)
    • transactionManager
    • dataSource (data source)
• mappers

properties

MybatisConfig.xml can refer to the configuration information in the java property file as follows:

Define the db.properties file under the classpath

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/data
jdbc.username=root
jdbc.password=root

mybatisConfig.xml is quoted as follows

<properties resource="db.properties"></properties>
<environments default="development">
	<environment id="development">
		<transactionManager type="JDBC" />
		<dataSource type="POOLED">
			<property name="driver" value="${jdbc.driver}" />
			<property name="url" value="${jdbc.url}" />
			<property name="username" value="${jdbc.username}" />
			<property name="password" value="${jdbc.password}" />
		</dataSource>
	</environment>
</environments>

Note: MyBatis will load the properties in the following order:

• The properties defined in the properties element body are read first.
• Then it will read the attribute loaded by resource or url in the properties element, and it will overwrite the attribute of the same name that has been read.
• Finally read the attribute passed by parameterType, it will overwrite the attribute of the same name that has been read.

Therefore, the attribute passed through parameterType has the highest priority, followed by the attribute loaded by resource or url, and the lowest priority is the attribute defined in the properties element body.

settings

Mybatis global configuration parameters, global parameters will affect the running behavior of mybatis. An example of a fully configured settings element is as follows:

<settings>
  <setting name="cacheEnabled" value="true"/>
  <setting name="lazyLoadingEnabled" value="true"/>
  <setting name="multipleResultSetsEnabled" value="true"/>
  <setting name="useColumnLabel" value="true"/>
  <setting name="useGeneratedKeys" value="false"/>
  <setting name="autoMappingBehavior" value="PARTIAL"/>
  <setting name="autoMappingUnknownColumnBehavior" value="WARNING"/>
  <setting name="defaultExecutorType" value="SIMPLE"/>
  <setting name="defaultStatementTimeout" value="25"/>
  <setting name="defaultFetchSize" value="100"/>
  <setting name="safeRowBoundsEnabled" value="false"/>
  <setting name="mapUnderscoreToCamelCase" value="false"/>
  <setting name="localCacheScope" value="SESSION"/>
  <setting name="jdbcTypeForNull" value="OTHER"/>
  <setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/>
</settings>

Setting parameters	description	Effective value	Defaults
cacheEnabled	Globally turn on or off any cache that has been configured by all mappers in the configuration file.	true | false	TRUE
lazyLoadingEnabled	Global switch for delayed loading. When turned on, all associated objects will be lazily loaded. You can set the fetchType property to override the on-off status of the item in a specific association.	true | false	FALSE
aggressiveLazyLoading	When turned on, any method call will load all properties of the object. Otherwise, each property will be loaded as needed (refer to lazyLoadTriggerMethods).	true | false	false (true in ≤3.4.1)
multipleResultSetsEnabled	Whether to allow a single statement to return multiple result sets (requires compatible drivers).	true | false	TRUE
useColumnLabel	Use column labels instead of column names. Different drivers will have different performances in this regard. For details, please refer to the relevant driver documentation or test these two different modes to observe the results of the drivers used.	true | false	TRUE
useGeneratedKeys	To allow JDBC to support automatic generation of primary keys, driver compatibility is required. If set to true, this setting forces the use of automatically generated primary keys, although some drivers are not compatible but can still work normally (such as Derby).	true | false	FALSE
autoMappingBehavior	Specify how MyBatis should automatically map columns to fields or properties. NONE means cancel automatic mapping; PARTIAL will only automatically map result sets that do not define nested result set mappings. FULL will automatically map any complex result set (whether or not nested).	NONE, PARTIAL, FULL	PARTIAL
autoMappingUnknownColumnBehavior	Specify the behavior of automatically discovering the target unknown column (or unknown attribute type).	NONE, WARNING, FAILING	NONE
	NONE: No response
	WARNING: Output reminder log ('org.apache.ibatis.session.AutoMappingUnknownColumnBehavior' log level must be set to WARN)
	FAILING: Mapping failed (throw SqlSessionException)
defaultExecutorType	Configure the default actuator. SIMPLE is an ordinary executor; the REUSE executor will reuse prepared statements; the BATCH executor will reuse statements and perform batch updates.	SIMPLE REUSE BATCH	SIMPLE
defaultStatementTimeout	Set the timeout period, which determines the number of seconds the driver waits for a response from the database.	Any positive integer	Not Set (null)
defaultFetchSize	Set a hint value for the number of fetched result sets (fetchSize). This parameter can only be overridden in the query settings.	Any positive integer	Not Set (null)
safeRowBoundsEnabled	Allow pagination (RowBounds) in nested statements. Set to false if allowed.	true | false	FALSE
safeResultHandlerEnabled	Allow paging (ResultHandler) in nested statements. Set to false if allowed.	true | false	TRUE
mapUnderscoreToCamelCase	Whether to enable automatic camel case naming rule (camel case) mapping, that is, a similar mapping from the classic database column name A_COLUMN to the classic Java property name aColumn.	true | false	FALSE
localCacheScope	MyBatis uses Local Cache to prevent circular references and accelerate repeated nested queries. The default value is SESSION, in which case all queries executed in one session will be cached. If the setting value is STATEMENT, the local session is only used for statement execution, and different calls to the same SqlSession will not share data.	SESSION | STATEMENT	SESSION
jdbcTypeForNull	When no specific JDBC type is provided for the parameter, specify the JDBC type for the null value. Some drivers need to specify the JDBC type of the column. In most cases, the general type can be used directly, such as NULL, VARCHAR, or OTHER.	JdbcType constants. Most of them are: NULL, VARCHAR and OTHER	OTHER
lazyLoadTriggerMethods	The method of specifying which object triggers a lazy load.	A comma-separated list of methods.	equals,clone,hashCode,toString
defaultScriptingLanguage	Specify the default language for dynamic SQL generation.	一个类型别名或完全限定类名。	org.apache.ibatis.scripting.xmltags.XMLLanguageDriver
defaultEnumTypeHandler	指定 Enum 使用的默认 TypeHandler 。 (从3.4.5开始)	一个类型别名或完全限定类名。	org.apache.ibatis.type.EnumTypeHandler
callSettersOnNulls	指定当结果集中值为 null 的时候是否调用映射对象的 setter（map 对象时为 put）方法，这对于有 Map.keySet() 依赖或 null 值初始化的时候是有用的。注意基本类型（int、boolean等）是不能设置成 null 的。	true | false	FALSE
returnInstanceForEmptyRow	当返回行的所有列都是空时，MyBatis默认返回null。 当开启这个设置时，MyBatis会返回一个空实例。 请注意，它也适用于嵌套的结果集 (i.e. collectioin and association)。（从3.4.2开始）	true | false	FALSE
logPrefix	指定 MyBatis 增加到日志名称的前缀。	任何字符串	Not set
logImpl	指定 MyBatis 所用日志的具体实现，未指定时将自动查找。	SLF4J | LOG4J | LOG4J2 | JDK_LOGGING | COMMONS_LOGGING | STDOUT_LOGGING | NO_LOGGING	Not set
proxyFactory	指定 Mybatis 创建具有延迟加载能力的对象所用到的代理工具。	CGLIB | JAVASSIST	JAVASSIST (MyBatis 3.3 or above)
vfsImpl	指定VFS的实现	自定义VFS的实现的类全限定名，以逗号分隔。	Not set
useActualParamName	允许使用方法签名中的名称作为语句参数名称。 为了使用该特性，你的工程必须采用Java 8编译，并且加上-parameters选项。（从3.4.1开始）	true | false	TRUE
configurationFactory	指定一个提供Configuration实例的类。 这个被返回的Configuration实例用来加载被反序列化对象的懒加载属性值。 这个类必须包含一个签名方法static Configuration getConfiguration(). (从 3.2.3 版本开始)	类型别名或者全类名.	Not set

 typeAliases（类型别名）

别名	映射的类型
_byte	byte
_long	long
_short	short
_int	int
_integer	int
_double	double
_float	float
_boolean	boolean
string	String
byte	Byte
long	Long
short	Short
int	Integer
integer	Integer
double	Double
float	Float
boolean	Boolean
date	Date
decimal	BigDecimal
bigdecimal	BigDecimal
object	Object
map	Map
hashmap	HashMap
list	List
arraylist	ArrayList
collection	Collection
iterator	Iterator

自定义别名：

<typeAliases>
	<!-- 单个别名定义 -->
	<typeAlias alias="user" type="org.haiwen.entity.User"/>
	<!-- 批量别名定义，扫描整个包下的类，别名为类名（首字母大写或小写都可以） -->
	<package name="org.haiwen.entity"/>
	<package name="其它包"/>
</typeAliases>

typeHandlers（类型处理器）

无论是 MyBatis 在预处理语句（PreparedStatement）中设置一个参数时，还是从结果集中取出一个值时， 都会用类型处理器将获取的值以合适的方式转换成 Java 类型。

类型处理器	Java 类型	JDBC 类型
BooleanTypeHandler	java.lang.Boolean, boolean	数据库兼容的 BOOLEAN
ByteTypeHandler	java.lang.Byte, byte	数据库兼容的 NUMERIC 或 BYTE
ShortTypeHandler	java.lang.Short, short	数据库兼容的 NUMERIC 或 SHORT INTEGER
IntegerTypeHandler	java.lang.Integer, int	数据库兼容的 NUMERIC 或 INTEGER
LongTypeHandler	java.lang.Long, long	数据库兼容的 NUMERIC 或 LONG INTEGER
FloatTypeHandler	java.lang.Float, float	数据库兼容的 NUMERIC 或 FLOAT
DoubleTypeHandler	java.lang.Double, double	数据库兼容的 NUMERIC 或 DOUBLE
BigDecimalTypeHandler	java.math.BigDecimal	数据库兼容的 NUMERIC 或 DECIMAL
StringTypeHandler	java.lang.String	CHAR, VARCHAR
ClobReaderTypeHandler	java.io.Reader	-
ClobTypeHandler	java.lang.String	CLOB, LONGVARCHAR
NStringTypeHandler	java.lang.String	NVARCHAR, NCHAR
NClobTypeHandler	java.lang.String	NCLOB
BlobInputStreamTypeHandler	java.io.InputStream	-
ByteArrayTypeHandler	byte[]	数据库兼容的字节流类型
BlobTypeHandler	byte[]	BLOB, LONGVARBINARY
DateTypeHandler	java.util.Date	TIMESTAMP
DateOnlyTypeHandler	java.util.Date	DATE
TimeOnlyTypeHandler	java.util.Date	TIME
SqlTimestampTypeHandler	java.sql.Timestamp	TIMESTAMP
SqlDateTypeHandler	java.sql.Date	DATE
SqlTimeTypeHandler	java.sql.Time	TIME
ObjectTypeHandler	Any	OTHER 或未指定类型
EnumTypeHandler	Enumeration Type	VARCHAR-任何兼容的字符串类型，存储枚举的名称（而不是索引）
EnumOrdinalTypeHandler	Enumeration Type	任何兼容的 NUMERIC 或 DOUBLE 类型，存储枚举的索引（而不是名称）。
InstantTypeHandler	java.time.Instant	TIMESTAMP
LocalDateTimeTypeHandler	java.time.LocalDateTime	TIMESTAMP
LocalDateTypeHandler	java.time.LocalDate	DATE
LocalTimeTypeHandler	java.time.LocalTime	TIME
OffsetDateTimeTypeHandler	java.time.OffsetDateTime	TIMESTAMP
OffsetTimeTypeHandler	java.time.OffsetTime	TIME
ZonedDateTimeTypeHandler	java.time.ZonedDateTime	TIMESTAMP
YearTypeHandler	java.time.Year	INTEGER
MonthTypeHandler	java.time.Month	INTEGER
YearMonthTypeHandler	java.time.YearMonth	VARCHAR or LONGVARCHAR
JapaneseDateTypeHandler	java.time.chrono.JapaneseDate	DATE

mappers（映射器）

Mapper配置的几种方法：

使用相对于类路径的资源：<mapper resource=" " />
如：<mapper resource="sqlmap/User.xml" /> 

使用完全限定路径：<mapper url=" " />
如：<mapper url="file:///D:\workspace_spingmvc\mybatis_01\config\sqlmap\User.xml" />

使用mapper接口类路径：<mapper class=" " />
如：<mapper class="cn.itcast.mybatis.mapper.UserMapper"/>
注意：此种方法要求mapper接口名称和mapper映射文件名称相同，且放在同一个目录中。

注册指定包下的所有mapper接口：<package name=""/>
如：<package name="cn.itcast.mybatis.mapper"/>
注意：此种方法要求mapper接口名称和mapper映射文件名称相同，且放在同一个目录中。