mybatis typeHandler

typeHandler是类型转换器。如果你需要将一个枚举类型的数据存放到数据库，而数据库不支持枚举类型，所以需要将它保存为一个数值类型。那么，如何实现数据库类型和java枚举类型的相互转换呢？使用自定义的类型转换器即可。自定义的类型转换器需要实现typeHandler接口。

下面是一个枚举类型的定义：

public enum Role {USER(0, "普通用户"), MANAGER(1, "管理员");private int code;private String text;private Role(int code, String text) {this.code = code;this.text = text;}public int code() {return code;}public String text() {return text;}public static Role codeOf(int code) {for (Role role : values()) {if (role.code == code) {return role;}}throw new IllegalArgumentException("Invalid role code: " + code);}}

我们定义一个自定义的类型转换器，如下：

import java.sql.CallableStatement;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import org.apache.ibatis.type.JdbcType;import org.apache.ibatis.type.TypeHandler;public class RoleTypeHandler implements TypeHandler<Role> {@Overridepublic void setParameter(PreparedStatement ps, int i, Role parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.code());}@Overridepublic Role getResult(ResultSet rs, String columnName) throws SQLException {return Role.codeOf(rs.getInt(columnName));}@Overridepublic Role getResult(ResultSet rs, int columnIndex) throws SQLException {return Role.codeOf(rs.getInt(columnIndex));}@Overridepublic Role getResult(CallableStatement cs, int columnIndex) throws SQLException {return Role.codeOf(cs.getInt(columnIndex));}}

接下来，需要注册自定义的类型转换器

<configuration>    <typeHandlers>        <typeHandler handler="com.mybatis.demo.RoleTypeHandler" javaType="com.mybatis.demo.Role" />    </typeHandlers><environments default="development"><environment id="development"><transactionManager type="JDBC" /><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver" /><property name="url" value="jdbc:mysql://localhost:3306/mybatis_test" /><property name="username" value="root" /><property name="password" value="root" /></dataSource></environment></environments><mappers><!--省略 /--></mappers></configuration> 

mapper文件如下：

<mapper namespace="account">    <select id="select"            parameterType="java.util.HashMap"            resultType="com.mybatis.demo.Account">        <![CDATA[            select                id,                name,                password,                role,                created,                last_login_time as lastLoginTime            from                 account        ]]>        <where>            <if test="name !=null and name != ''">                and name = #{name}            </if>            <if test="role != null">            and role=#{role}            </if>            <if test="id != null">            and id = #{id}            </if>        </where>    </select></mapper>

接下来编写测试类，就可以发现已经能实现java类型和数据库类型的自动换转了。测试类如下：

public class test {    public static void main(String[] args) throws IOException {        String config = "mybatis-config-standalone.xml";        InputStream inputStream = Resources.getResourceAsStream(config);        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);        SqlSession sqlSession = sessionFactory.openSession();        Map<String, Object> params = new LinkedHashMap<String, Object>();        params.put("name", "frank");        Account account = sqlSession.selectOne("account.select",params);        System.out.println(account);    }}