Simple use of stream (II)

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Preface

demand ： I need to give List Properties of objects in phone Assign a value , And then back to the front end . Current properties phone The value of is in another table .

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Tips ： The following is the main body of this article , The following cases can be used for reference

One 、 Use steps

1. Sample code

        List<MecReceiveLine> mecReceiveLines = mapper.selectByDepartId(departId);
        // Convert to  VO
        List<MecReceiveLineVO> mecReceiveLineVOS = BeanHelper.copyWithCollection(mecReceiveLines, MecReceiveLineVO.class);

        List<String> departIds = mecReceiveLines.stream().map(mecReceiveLine -> mecReceiveLine.getDepartId())
                .collect(Collectors.toList());
        List<MecDepartInfo> mecDepartInfoList = mecDepartInfoBiz.selectByIds(departIds);
        //  Collect to List,

        //  take List Object to map;(Function.identity()) Use objects as value.
        /** *  Take the primary key of the object id, effect key, Ensure accurate correspondence . */
        Map<String, MecDepartInfo> collect = mecDepartInfoList.stream().collect(Collectors.toMap(MecDepartInfo::getCustPk, Function.identity()));
        //  The goal is ： loop VOS object , For its phone Property to assign . Processing must be the target object , It's assigned , It is also where the demand lies .
        for (MecReceiveLineVO mecReceiveLineVO : mecReceiveLineVOS) {
    
            MecDepartInfo mecDepartInfo = collect.get(mecReceiveLineVO.getDepartId());
            if (mecDepartInfo != null){
    
                mecReceiveLineVO.setPhoneNumber(mecDepartInfo.getCustMobile());
            }
        }

2. Interface profile (SQL)

<!-- Batch query -->
<select id="selectByDepartIds" resultType="com.guanke.dmp.mec.entity.MecDepartInfo">
    select
    *
    from mec_depart_info
    where ( 1 = 1 )
    <if test="departIds != null and departIds.size != 0">
        and cust_pk in
        <foreach collection="departIds" item="item" open=" ( " close=" ) " separator=",">
            #{item}
        </foreach>
    </if>
</select>

Here we use Subquery and dynamic sql.

3.Bean Tool class

/** * @author Yingyu Wei * @date 2020-03-18 */
@Slf4j
public class BeanHelper {
    
    
    public static <T> T copyProperties(Object source, Class<T> target){
    
        try {
    
            T t = target.newInstance();
            BeanUtils.copyProperties(source, t);
            return t;
        } catch (Exception e) {
    
            log.error("【 Data conversion 】 Data conversion error , Target audience {} Constructor exception ", target.getName(), e);
            throw new RuntimeException("【 Data conversion 】 Data conversion error ");
        }
    }

    public static <T> List<T> copyWithCollection(List<?> sourceList, Class<T> target){
    
        try {
    
            return sourceList.stream().map(s -> copyProperties(s, target)).collect(Collectors.toList());
        } catch (Exception e) {
    
            log.error("【 Data conversion 】 Data conversion error , Target audience {} Constructor exception ", target.getName(), e);
                        throw new RuntimeException("【 Data conversion 】 Data conversion error ");
        }

    }

    public static <T> Set<T> copyWithCollection(Set<?> sourceList, Class<T> target){
    
        try {
    
            return sourceList.stream().map(s -> copyProperties(s, target)).collect(Collectors.toSet());
        } catch (Exception e) {
    
            log.error("【 Data conversion 】 Data conversion error , Target audience {} Constructor exception ", target.getName(), e);
                        throw new RuntimeException("【 Data conversion 】 Data conversion error ");
        }
    }
}

Add

Example 2

demand ： Need to be right List The attribute assignment of the object in the .
Use ：forEach() Method , Instead of using streams .

// skuList.stream().map(sku1 -> sku1.setSpuId(spuDTO.getId()));  error 
skuList.forEach(sku1 -> sku1.setSpuId(spuDTO.getId()));

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summary

Summary of notes :
1, to List When assigning a property in , Need to traverse , Just use stream Flow through row operation .
1.1, Sample code 1 The attributes of objects in requirements are variable ; Sample code 2 The attribute values of objects in requirements are fixed , So use forEach() Faster .
2,list Convert to map when , Streams can also be used , And use list Object id( It's usually used id, Because it doesn't repeat , accord with key The requirements of .) As key, Using objects as Value.

// @AllArgsConstructor
Recommended articles ：link.s

2021 year 3 month 25 Japan
Add ： The value of the object property does not change , It can be used forEach().(ps： This is not a stream operation )