MyBatis 之配置文件 TypeHandler 元素

2015-08-11

MyBatis 版本：MyBatis 3.3.0

MyBatis 官方网站（英文）：MyBatis 英文官网
MyBatis 官方网站（中文）：MyBatis 中文官网
MyBatis 源码：MyBatis 源码

MyBatis 配置文件层次结构

<?xml version="1.0" encoding="UTF-8">
<configuration> <!--配置-->
  <properties/> <!--属性-->
  <settings/> <!--设置-->
  <typeAliases/> <!--类型命名-->
  <typeHandlers/> <!--类型处理器-->
  <objetFactory/> <!--对象工厂-->
  <plugins/> <!--插件-->
  <environments> <!--配置环境-->
    <environment> <!--环境变量-->
      <transactionManager/> <!--事务管理器-->
      <dataSource/> <!--数据源-->
    </environment>
  </environments>
  <databaseIdProvider/> <!--数据库厂商标识-->
  <mappers/> <!--映射器-->
</configuration>

TypeHandler 元素

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。

TypeHandler 的作用就是将参数从 javaType 转化为 jdbcType，或者从数据库取出结果时把 jdbcType 转化为 javaType。

TypeHandler 可分为：

系统定义的 TypeHandler
自定义的 TypeHandler

系统定义的 TypeHandler

MyBatis org.apache.ibatis.type.TypeHandlerRegistry 类中定义了所有的系统定义的 TypeHandler:

public TypeHandlerRegistry() {
    this.register((Class)Boolean.class, (TypeHandler)(new BooleanTypeHandler()));
    this.register((Class)Boolean.TYPE, (TypeHandler)(new BooleanTypeHandler()));
    this.register((JdbcType)JdbcType.BOOLEAN, (TypeHandler)(new BooleanTypeHandler()));
    this.register((JdbcType)JdbcType.BIT, (TypeHandler)(new BooleanTypeHandler()));
    this.register((Class)Byte.class, (TypeHandler)(new ByteTypeHandler()));
    this.register((Class)Byte.TYPE, (TypeHandler)(new ByteTypeHandler()));
    this.register((JdbcType)JdbcType.TINYINT, (TypeHandler)(new ByteTypeHandler()));
    this.register((Class)Short.class, (TypeHandler)(new ShortTypeHandler()));
    this.register((Class)Short.TYPE, (TypeHandler)(new ShortTypeHandler()));
    this.register((JdbcType)JdbcType.SMALLINT, (TypeHandler)(new ShortTypeHandler()));
    this.register((Class)Integer.class, (TypeHandler)(new IntegerTypeHandler()));
    this.register((Class)Integer.TYPE, (TypeHandler)(new IntegerTypeHandler()));
    this.register((JdbcType)JdbcType.INTEGER, (TypeHandler)(new IntegerTypeHandler()));
    this.register((Class)Long.class, (TypeHandler)(new LongTypeHandler()));
    this.register((Class)Long.TYPE, (TypeHandler)(new LongTypeHandler()));
    this.register((Class)Float.class, (TypeHandler)(new FloatTypeHandler()));
    this.register((Class)Float.TYPE, (TypeHandler)(new FloatTypeHandler()));
    this.register((JdbcType)JdbcType.FLOAT, (TypeHandler)(new FloatTypeHandler()));
    this.register((Class)Double.class, (TypeHandler)(new DoubleTypeHandler()));
    this.register((Class)Double.TYPE, (TypeHandler)(new DoubleTypeHandler()));
    this.register((JdbcType)JdbcType.DOUBLE, (TypeHandler)(new DoubleTypeHandler()));
    this.register((Class)String.class, (TypeHandler)(new StringTypeHandler()));
    this.register((Class)String.class, JdbcType.CHAR, (TypeHandler)(new StringTypeHandler()));
    this.register((Class)String.class, JdbcType.CLOB, (TypeHandler)(new ClobTypeHandler()));
    this.register((Class)String.class, JdbcType.VARCHAR, (TypeHandler)(new StringTypeHandler()));
    this.register((Class)String.class, JdbcType.LONGVARCHAR, (TypeHandler)(new ClobTypeHandler()));
    this.register((Class)String.class, JdbcType.NVARCHAR, (TypeHandler)(new NStringTypeHandler()));
    this.register((Class)String.class, JdbcType.NCHAR, (TypeHandler)(new NStringTypeHandler()));
    this.register((Class)String.class, JdbcType.NCLOB, (TypeHandler)(new NClobTypeHandler()));
    this.register((JdbcType)JdbcType.CHAR, (TypeHandler)(new StringTypeHandler()));
    this.register((JdbcType)JdbcType.VARCHAR, (TypeHandler)(new StringTypeHandler()));
    this.register((JdbcType)JdbcType.CLOB, (TypeHandler)(new ClobTypeHandler()));
    this.register((JdbcType)JdbcType.LONGVARCHAR, (TypeHandler)(new ClobTypeHandler()));
    this.register((JdbcType)JdbcType.NVARCHAR, (TypeHandler)(new NStringTypeHandler()));
    this.register((JdbcType)JdbcType.NCHAR, (TypeHandler)(new NStringTypeHandler()));
    this.register((JdbcType)JdbcType.NCLOB, (TypeHandler)(new NClobTypeHandler()));
    this.register((Class)Object.class, JdbcType.ARRAY, (TypeHandler)(new ArrayTypeHandler()));
    this.register((JdbcType)JdbcType.ARRAY, (TypeHandler)(new ArrayTypeHandler()));
    this.register((Class)BigInteger.class, (TypeHandler)(new BigIntegerTypeHandler()));
    this.register((JdbcType)JdbcType.BIGINT, (TypeHandler)(new LongTypeHandler()));
    this.register((Class)BigDecimal.class, (TypeHandler)(new BigDecimalTypeHandler()));
    this.register((JdbcType)JdbcType.REAL, (TypeHandler)(new BigDecimalTypeHandler()));
    this.register((JdbcType)JdbcType.DECIMAL, (TypeHandler)(new BigDecimalTypeHandler()));
    this.register((JdbcType)JdbcType.NUMERIC, (TypeHandler)(new BigDecimalTypeHandler()));
    this.register((Class)Byte[].class, (TypeHandler)(new ByteObjectArrayTypeHandler()));
    this.register((Class)Byte[].class, JdbcType.BLOB, (TypeHandler)(new BlobByteObjectArrayTypeHandler()));
    this.register((Class)Byte[].class, JdbcType.LONGVARBINARY, (TypeHandler)(new BlobByteObjectArrayTypeHandler()));
    this.register((Class)byte[].class, (TypeHandler)(new ByteArrayTypeHandler()));
    this.register((Class)byte[].class, JdbcType.BLOB, (TypeHandler)(new BlobTypeHandler()));
    this.register((Class)byte[].class, JdbcType.LONGVARBINARY, (TypeHandler)(new BlobTypeHandler()));
    this.register((JdbcType)JdbcType.LONGVARBINARY, (TypeHandler)(new BlobTypeHandler()));
    this.register((JdbcType)JdbcType.BLOB, (TypeHandler)(new BlobTypeHandler()));
    this.register(Object.class, this.UNKNOWN_TYPE_HANDLER);
    this.register(Object.class, JdbcType.OTHER, this.UNKNOWN_TYPE_HANDLER);
    this.register(JdbcType.OTHER, this.UNKNOWN_TYPE_HANDLER);
    this.register((Class)Date.class, (TypeHandler)(new DateTypeHandler()));
    this.register((Class)Date.class, JdbcType.DATE, (TypeHandler)(new DateOnlyTypeHandler()));
    this.register((Class)Date.class, JdbcType.TIME, (TypeHandler)(new TimeOnlyTypeHandler()));
    this.register((JdbcType)JdbcType.TIMESTAMP, (TypeHandler)(new DateTypeHandler()));
    this.register((JdbcType)JdbcType.DATE, (TypeHandler)(new DateOnlyTypeHandler()));
    this.register((JdbcType)JdbcType.TIME, (TypeHandler)(new TimeOnlyTypeHandler()));
    this.register((Class)java.sql.Date.class, (TypeHandler)(new SqlDateTypeHandler()));
    this.register((Class)Time.class, (TypeHandler)(new SqlTimeTypeHandler()));
    this.register((Class)Timestamp.class, (TypeHandler)(new SqlTimestampTypeHandler()));
    this.register((Class)Character.class, (TypeHandler)(new CharacterTypeHandler()));
    this.register((Class)Character.TYPE, (TypeHandler)(new CharacterTypeHandler()));
}

汇总起来如下表格：

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 NUMBERIC 或 DOUBLE
BigDecimalTypeHandler	java.math.BigDecimal	数据库兼容的 NUMBERIC 或 DECIMAL
StringTypeHandler	java.lang.String	CHAR,VARCHAR
ClobTypeHandler	java.lang.String	CLOB,LONGVARCHAR
NStringTypeHandler	java.lang.String	NVARCHAR,NCHAR
NClobTypeHandler	java.lang.String	NCLOB
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 或任何兼容的字符串类型，存储枚举的名称
EnumOrdinalTypeHandler	Enumeration Type	任何兼容的NUMERIC 或 DOUBLE 类型，存储枚举的索引

自定义的 TypeHandler

自定义的 TypeHandler 比较少用，后续单独分析。