mybatis精通之路之TypeHandler初探

相关知识，可以参考

https://blog.csdn.net/chenbaige/article/details/72568959

这里，主要是说明TypeHandler的生效顺序的。

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)Reader.class, (TypeHandler)(new ClobReaderTypeHandler()));
        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)InputStream.class, (TypeHandler)(new BlobInputStreamTypeHandler()));
        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()));
        if (Jdk.dateAndTimeApiExists) {
            Java8TypeHandlersRegistrar.registerDateAndTimeHandlers(this);
        }


        this.register((Class)Character.class, (TypeHandler)(new CharacterTypeHandler()));
        this.register((Class)Character.TYPE, (TypeHandler)(new CharacterTypeHandler()));

    }

项目中，新注册了一个BooleanTypeHandler，用于将boolean类型的值转化成字符串TRUE或FALSE。但是在查询时，总是会报错，原因是在查询语句中，没有指定属性的jdbcType，所以mybatis使用了默认的处理类。这里，执行查询字段的jdbcType类型即可解决。

Map<String,Object> param = new HashMap<>();
param.put("booleantest",Boolean.TRUE);

<select id="selectUser" parameterType="map" resultMap="BaseResultMap">
    select * from user
    <where>
      1 = 1
      <if test="name != null">
        and name = #{name}
      </if>
      <if test="code != null">
        and code = #{code}
      </if>
      <if test="booleantest != null">
        and booleantest = #{booleantest,jdbcType=VARCHAR}
      </if>
    </where>
  </select>