后端Java Stream数据流的使用=＞代替for循环

API讲解 

对比 

示例代码对比

for循环遍历 

package cn.ryanfan.platformback.service.impl;import cn.ryanfan.platformback.entity.Algorithm;
import cn.ryanfan.platformback.entity.AlgorithmCategory;
import cn.ryanfan.platformback.entity.DTO.AlgorithmInfoDTO;
import cn.ryanfan.platformback.mapper.AlgorithmCategoryMapper;
import cn.ryanfan.platformback.mapper.AlgorithmMapper;
import cn.ryanfan.platformback.service.IAlgorithmService;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;import java.util.ArrayList;
import java.util.List;/*** <p>*  服务实现类* </p>** @author 刘一帆* @since 2025-02-20*/
@Service
@RequiredArgsConstructor
public class AlgorithmServiceImpl extends ServiceImpl<AlgorithmMapper, Algorithm> implements IAlgorithmService {private final AlgorithmMapper algorithmMapper;private final AlgorithmCategoryMapper algorithmCategoryMapper;@Overridepublic List<AlgorithmInfoDTO> selectAllAlgorithmInfo() {//  最终数据List<AlgorithmInfoDTO> result = new ArrayList<>();//  查询algorithm表数据List<Algorithm> algorithmList = algorithmMapper.selectList(null);// 查询category表数据 存于Mapfor(Algorithm algorithm : algorithmList){AlgorithmInfoDTO algorithmInfoDTO = new AlgorithmInfoDTO();algorithmInfoDTO.setId(algorithm.getId());algorithmInfoDTO.setName(algorithm.getName());algorithmInfoDTO.setStatus(algorithm.getStatus());//设置DTO的category_Name 旧方法：在for循环中进行查询（每一次for都在查询） 新方法：将category表新查出=>存于Map=>每次遍历这个MapLambdaQueryWrapper<AlgorithmCategory> lambdaQueryWrapper = new LambdaQueryWrapper<>();lambdaQueryWrapper.eq(AlgorithmCategory::getId,algorithm.getCategoryId());algorithmInfoDTO.setCategoryName(algorithmCategoryMapper.selectOne(lambdaQueryWrapper).getName());result.add(algorithmInfoDTO);}return result;}
}

stream流式处理

package cn.ryanfan.platformback.service.impl;import cn.ryanfan.platformback.entity.Algorithm;
import cn.ryanfan.platformback.entity.AlgorithmCategory;
import cn.ryanfan.platformback.entity.DTO.AlgorithmInfoDTO;
import cn.ryanfan.platformback.mapper.AlgorithmCategoryMapper;
import cn.ryanfan.platformback.mapper.AlgorithmMapper;
import cn.ryanfan.platformback.service.IAlgorithmService;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;/*** <p>*  服务实现类* </p>** @author 刘一帆* @since 2025-02-20*/
@Service
@RequiredArgsConstructor
public class AlgorithmServiceImpl extends ServiceImpl<AlgorithmMapper, Algorithm> implements IAlgorithmService {private final AlgorithmMapper algorithmMapper;private final AlgorithmCategoryMapper algorithmCategoryMapper;@Overridepublic List<AlgorithmInfoDTO> selectAllAlgorithmInfo() {//  查询algorithm表数据List<Algorithm> algorithmList = algorithmMapper.selectList(null);// 查询category表数据 存于Map 查询所有的分类数据，避免逐个查询List<AlgorithmCategory> categoryList = algorithmCategoryMapper.selectList(null);Map<Integer,String> categoryMap = categoryList.stream().collect(Collectors.toMap(AlgorithmCategory::getId,AlgorithmCategory::getName));//  最终数据List<AlgorithmInfoDTO> result  = algorithmList.stream().map(algorithm -> {AlgorithmInfoDTO algorithmInfoDTO = new AlgorithmInfoDTO();algorithmInfoDTO.setId(algorithm.getId());algorithmInfoDTO.setName(algorithm.getName());algorithmInfoDTO.setStatus(algorithm.getStatus());// 通过分类 id 获取分类名称String categoryName = categoryMap.get(algorithm.getCategoryId());algorithmInfoDTO.setCategoryName(categoryName != null ? categoryName : "未知分类");return algorithmInfoDTO;}).collect(Collectors.toList());return result;}
}