Mybatis枚举转换

自定义mybatis枚举转换，原理是如果用户没有定义自己的枚举转换工具，mybatis在解析枚举类时会自动获取mybatis的BaseTypeHandler，来转换枚举类，我们只需要重写这个枚举转换器，并将它指定为默认的转换器就好了

首先，定义一个通用接口BaseEnum：

import java.util.Arrays;
import java.util.Optional;

public interface BaseEnum<T>{

    T getDictKey();

    default T getValue() {
        return this.getDictKey();
    }

    static <T> BaseEnum valueOfEnum(Class<BaseEnum> enumClass, T value){
        if (value == null){
            return null;
        }
        BaseEnum[] enums = enumClass.getEnumConstants();
        Optional<BaseEnum> optional = Arrays.asList(enums).stream().filter(baseEnum -> baseEnum.getDictKey().equals(value)).findAny();
        if (optional.isPresent()){
            return optional.get();
        }
        throw new RuntimeException("未找到：" + value + "对应的" + enumClass.getName());
    }
}

然后，定义一个枚举解析器MyEnumTypeHandler，该枚举类继承自BaseTypeHandler：

import com.bluepay.spring.mybatis.demo.BaseEnum;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class MyEnumTypeHandler<T> extends BaseTypeHandler<BaseEnum<T>> {
    private final Class<BaseEnum> type;

    public MyEnumTypeHandler(Class<BaseEnum> type) {
        this.type = type;
    }

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, BaseEnum parameter, JdbcType jdbcType) throws SQLException {
        System.out.println("set value");
        if (jdbcType == null) {
            ps.setString(i, (String) parameter.getDictKey());
        } else {
            ps.setObject(i, parameter.getDictKey(), jdbcType.TYPE_CODE); // see r3589
        }
    }

    @Override
    public BaseEnum getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String s = rs.getString(columnName);
        return s == null ? null : BaseEnum.valueOfEnum(type, s);
    }

    @Override
    public BaseEnum getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String s = rs.getString(columnIndex);
        return s == null ? null : BaseEnum.valueOfEnum(type, s);
    }

    @Override
    public BaseEnum getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String s = cs.getString(columnIndex);
        return s == null ? null : BaseEnum.valueOfEnum(type, s);
    }
}

最后，将该枚举解析器配置为mybatis的默认枚举解析器，mybatis-config.xml配置如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true" />
    </settings>
    <typeHandlers>
        <typeHandler handler="com.bluepay.spring.mybatis.config.MyEnumTypeHandler" javaType="com.bluepay.spring.mybatis.demo.BaseEnum"></typeHandler>
    </typeHandlers>
  
</configuration>

至此，默认的枚举转换类型定义完成，用户的枚举类只要实现BaseEnum接口，就可以被正确的解析了

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