MyBatis中的自定义TypeHandler详解

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.ResultSet;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;
import org.apache.log4j.Logger;
public class MyTypeHandler implements TypeHandler<String> {
    Logger logger = Logger.getLogger(MyTypeHandler.class);
    @Override
    public void setParameter(PreparedStatement ps, int i, String parameter,
            JdbcType jdbcType) throws SQLException {
        logger.info("设置 string 参数【" + parameter + "】");
        ps.setString(i, parameter);
    }
    @Override
    public String getResult(ResultSet rs, String columnName)
            throws SQLException {
        String result = rs.getString(columnName);
        logger.info("读取 string 参数 1 【" + result + "】");
        return result;
    }
    @Override
    public String getResult(ResultSet rs, int columnIndex) throws SQLException {
        String result = rs.getString(columnIndex);
        logger.info("读取string 参数 2【" + result + "】");
        return result;
    }
    @Override
    public String getResult(CallableStatement cs, int columnIndex)
            throws SQLException {
        String result = cs.getString(columnIndex);
        logger.info("读取 string 参数 3 【" + result + "】");
        return result;
    }
}

<typeHandlers>
    <typeHandler jdbcType="VARCHAR" javaType="string" handler="com.mybatis.test.MyTypeHandler"/>
</typeHandlers>

....
<resultMap id="roleMapper" type="role">
    <result property="id" column="id"/>
    <result property="roleName" column="role_name" jdbcType="VARCHAR" javaType="string"/>
    <result property="note" column="note" typeHandler=" com.mybatis.test.MyTypeHandler"/>
</resultMap>
<select id="getRole" parameterType="long" resultMap="roleMapper">
    select id,role_name,note from t_role where id = #{id}
</select>
<select id="findRoles" parameterType="string" resultMap="roleMapper">
    select id, role_name, note from t_role
    where role_name like concat('%',#{roleName, jdbcType=VARCHAR,
    javaType=string}, '%')
</select>
<select id="findRoles2" parameterType="string" resultMap="roleMapper">
    select id, role_name, note from t_role
    where note like concat ('%', # {note, typeHandler=com.mybatis.test.MyTypeHandler},'%')
</select>
......

<typeHandlertype>
    <package name="com.mybatis.test"/>
</typeHandlertype>

@MappedTypes(String.class)
@MappedjdbcTypes(jdbcType.VARCHAR)
public class MyTypeHandler implements TypeHandler<String>{
    ......
}