MyBatis返回Map键值对数据Key值改小写

以你之姓@ 2023-03-12 14:30 3阅读 0赞

--场景一：
    select code,name,addr from users
    ---场景二：
    select * from users

使用MyBatis查询且`resultType=Map`时，如果未做任何配置，以上两个SQL查询结果均如下：

[{ 
    	CODE: '1',
    	NAME: '张三',
    	ADDR: '上海'
    }]

我希望将键值改为小写：

### 方法一：设置返回字段的别名 ###

对于场景一，我们可以给每个查询字段加个别名，如下：

select 
    	code as "code",
    	name as "name",
    	addr as "addr"
    from users

但加别名的方式不适用于场景二。

### 方法二：通用方法(推荐) ###

*  步骤一：创建类`MapKeyLowerWrapper.java`，继承`MapWrapper`。该类将查询结果转换成Map。

package com.example.demo.filter;
    import org.apache.ibatis.reflection.MetaObject;
    import org.apache.ibatis.reflection.wrapper.MapWrapper;
    import java.util.Map;
    /** * 将Map的key全部转换为小写 */
    public class MapKeyLowerWrapper extends MapWrapper { 
    
        public MapKeyLowerWrapper(MetaObject metaObject, Map<String, Object> map) { 
            super(metaObject, map);
        }
    
        @Override
        public String findProperty(String name, boolean useCamelCaseMapping) { 
            return name == null ? "" : name.toLowerCase();
        }
    }

步骤二：创建类`MapWrapperFactory.java`。该类引用调用刚创建的自定义转换类`MapKeyLowerWrapper`

package com.example.demo.filter;
    
    import org.apache.ibatis.reflection.MetaObject;
    import org.apache.ibatis.reflection.wrapper.ObjectWrapper;
    import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;
    
    import java.util.Map;
    
    public class MapWrapperFactory implements ObjectWrapperFactory { 
    
        @Override
        public boolean hasWrapperFor(Object object) { 
            return object != null && object instanceof Map;
        }
    
        @Override
        public ObjectWrapper getWrapperFor(MetaObject metaObject, Object object) { 
            return new MapKeyLowerWrapper(metaObject, (Map) object);
        }
    }

步骤三：创建类`ObjectWrapperFactoryConverter.java`

package com.example.demo.filter;
    
    import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;
    import org.springframework.boot.context.properties.ConfigurationPropertiesBinding;
    import org.springframework.core.convert.converter.Converter;
    import org.springframework.stereotype.Component;
    
    
    @Component
    @ConfigurationPropertiesBinding
    public class ObjectWrapperFactoryConverter implements Converter<String, ObjectWrapperFactory> { 
        @Override
        public ObjectWrapperFactory convert(String source) { 
            try { 
                return (ObjectWrapperFactory) Class.forName(source).newInstance();
            } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) { 
                throw new RuntimeException(e);
            }
        }
    }

步骤四：在yml中添加 MapWrapperFactory 的配置

#mybatis配置
    mybatis-plus:
      mapper-locations: classpath:mapper/*.xml
      configuration:
        object-wrapper-factory: com.example.demo.filter.MapWrapperFactory

重启即可。