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MyBatis里字段到枚举类的映射

一、简介

  我们在用MyBatis里,很多时间有这样一个需求:bean里有个属性是枚举,在DB存储时我们想存的枚举的代号,从DB拿出来时想直接映射成目标枚举类型,也即代号字段与Java枚举类的相互类型转换

  当然,你可以为每个枚举写一个MyEnumTypeHandler,但问题是要为每个类都写一个TypeHandler,过于繁琐。

  有了泛型,一个通用的TypeHandler直接搞定。

二、源码

源码详见:spring-mybatis-test

package com.adu.spring_test.mybatis.typehandler;import java.sql.CallableStatement;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import org.apache.ibatis.type.BaseTypeHandler;import org.apache.ibatis.type.JdbcType;import com.adu.spring_test.mybatis.enums.EnumTrait;import com.adu.spring_test.mybatis.util.EnumTraitUtil;/** * mapper里字段到枚举类的映射。 * 用法: * 入库:#{item.myEnum, typeHandler=com.adu.spring_test.mybatis.typehandler.EnumTraitTypeHandler} * 出库: * <resultMap> * <result property="enumDataField" column="enum_data_field" javaType="com.xxx.MyEnum" typeHandler="com.adu.spring_test.mybatis.typehandler.EnumTraitTypeHandler"/> * </resultMap> */public class EnumTraitTypeHandler<E extends EnumTrait> extends BaseTypeHandler<EnumTrait> {    private Class<E> type;    public EnumTraitTypeHandler(Class<E> type) {        if (type == null)            throw new IllegalArgumentException("Type argument cannot be null");        this.type = type;    }    @Override    public void setNonNullParameter(PreparedStatement ps, int i, EnumTrait parameter, JdbcType jdbcType)            throws SQLException {        ps.setInt(i, parameter.getCode());    }    @Override    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {        int i = rs.getInt(columnName);        if (rs.wasNull()) {            return null;        } else {            try {                return fromCode(i);            } catch (Exception ex) {                throw new IllegalArgumentException(                        "Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);            }        }    }    @Override    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {        int i = rs.getInt(columnIndex);        if (rs.wasNull()) {            return null;        } else {            try {                return fromCode(i);            } catch (Exception ex) {                throw new IllegalArgumentException(                        "Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);            }        }    }    @Override    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {        int i = cs.getInt(columnIndex);        if (cs.wasNull()) {            return null;        } else {            try {                return fromCode(i);            } catch (Exception ex) {                throw new IllegalArgumentException(                        "Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);            }        }    }    private E fromCode(int code) {        return EnumTraitUtil.codeOf(type, code);    }}

  

MyBatis里字段到枚举类的映射