mybatis中的TypeHandler设计与实现

TypeHandler主要是用在从java数据写入数据库时，从数据库中读取数据时的从java到jdbc类型之间的转换。

其类层次图为

TypeHandler：主要定义了设置参数、根据列名获取参数，列索引获取参数，从CallableStatement中根据列索引获取参数。

BaseTypeHandler：处理非NULL值的设置及获取参数

其他子类实现对应类型设置及参数获取

TypeHandlerRegistry：处理type到TypeHandler的映射关系

默认的映射关系有

javaType	jdbcType	typeHandler
Boolean.class	null	BooleanTypeHandler
boolean.class	null	BooleanTypeHandler
	JdbcType.Boolean	BooleanTypeHandler
	JdbcType.BIT	BooleanTypeHandler
Byte.class	null	ByteTypeHandler
byte.class	null	ByteTypeHandler
	JdbcType.TINYINT	ByteTypeHandler
Short.class	null	ShortTypeHandler
short.class	null	ShortTypeHandler
	JdbcType.SMALLINT	ShortTypeHandler
Integer.class	null	IntegerTypeHandler
int.class	null	IntegerTypeHandler
	JdbcType.INTEGER	IntegerTypeHandler
Long.class	null	LongTypeHandler
long.class	null	LongTypeHandler
Float.class	null	FloatTypeHandler
float.class	null	FloatTypeHandler
	JdbcType.FLOAT	FloatTypeHandler
Double.class	NULL	DoubleTypeHandler
double.class	NULL	DoubleTypeHandler
	JdbcType.DOUBLE	DoubleTypeHandler
Reader.class	null	ClobReaderTypeHandler
String.class	null	StringTypeHandler
String.class	JdbcType.CHAR	StringTypeHandler
String.class	JdbcType.CLOB	ClobTypeHandler
String.class	JdbcType.VARCHAR	StringTypeHandler
String.class	JdbcType.LONGVARCHAR	StringTypeHandler
String.class	JdbcType.NVARCHAR	NStringTypeHandler
String.class	JdbcType.NCHAR	NStringTypeHandler
String.class	JdbcType.NCLOB	NClobTypeHandler
	JdbcType.CHAR	StringTypeHandler
	JdbcType.VARCHAR	StringTypeHandler
	JdbcType.CLOB	ClobTypeHandler
	JdbcType.LONGVARCHAR	StringTypeHandler
	JdbcType.NVARCHAR	NStringTypeHandler
	JdbcType.NCHAR	NStringTypeHandler
	JdbcType.NCLOB	NClobTypeHandler
Object.class	JdbcType.ARRAY	ArrayTypeHandler
	JdbcType.ARRAY	ArrayTypeHandler
BigInteger.class	null	BigIntegerTypeHandler
	JdbcType.BIGINT	LongTypeHandler
BigDecimal	null	BigDecimalTypeHandler
	JdbcType.REAL	BigDecimalTypeHandler
	JdbcType.DECIMAL	BigDecimalTypeHandler
	JdbcType.NUMERIC	BigDecimalTypeHandler
InputStream.class	null	BlobInputStreamTypeHandler
Byte[].class	null	ByteObjectArrayTypeHandler
Byte[].class	JdbcType.BLOB	BlobByteObjectArrayTypeHandler
Byte[].class	JdbcType.LONGVARBINARY	BlobByteObjectArrayTypeHandler
byte[].class	null	ByteArrayTypeHandler
byte[].class	JdbcType.BLOB	BlobTypeHandler
byte[].class	JdbcType.LONGVARBINARY	BlobTypeHandler
	JdbcType.BLOB	BlobTypeHandler
	JdbcType.LONGVARBINARY	BlobTypeHandler
Date.class	null	DateTypeHandler
Date.class	JdbcType.DATE	DateOnlyTypeHandler
Date.class	JdbcType.TIME	TimeOnlyTypeHandler
	JdbcType.TIMESTAMP	DateTypeHandler
	JdbcType.DATE	DateOnlyTypeHandler
	JdbcType.TIME	TimeOnlyTypeHandler
java.sql.Date.class	null	SqlDateTypeHandler
java.sql.Time.class	null	SqlTimeTypeHandler
java.sql.Timestamp.class	null	SqlTimestampTypeHandler
String.class	JdbcType.SQLXML	SqlxmlTypeHandler
Instant.class	null	InstantTypeHandler
LocalDateTime.class	null	LocalDateTimeTypeHandler
LocalDate.class	null	LocalDateTypeHandler
LocalTime.class	null	LocalTimeTypeHandler
OffsetDateTime.class	null	OffsetDateTimeTypeHandler
OffsetTime.class	null	OffsetTimeTypeHandler
ZoneDateTime.class	null	ZoneDateTimeTypeHandler
Month.class	null	MonthTypeHandler
Year.class	null	YearTypeHandler
YearMonth.class	null	YearMonthTypeHandler
JapaneseDate.class	null	JapaneseDateTypeHandler
Character.class	null	CharacterTypeHandler
char.class	null	CharacterTypeHandler

原文链接：https://blog.csdn.net/wuli2496/article/details/108394138