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This article mainly introduces how to use JPA custom VO type conversion, the article is very detailed, has a certain reference value, interested friends must read it!

JPA Custom VO Type conversion (EntityUtils utility class)

In the JPA query, if you need to return a custom class, you can use the EntityUtils utility class, which is the source code:

Import org.slf4j.Logger;import org.slf4j.LoggerFactory; import java.lang.reflect.Constructor;import java.lang.reflect.Field;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map; / * * @ author 954L * @ create 17:27 on 2019-10-30 * / public class EntityUtils {private static final Logger log = LoggerFactory.getLogger (EntityUtils.class) / * convert array data to entity classes * where the order of array elements must be the same as the order of attributes in the entity class constructor * * @ param list array object collection * @ param clazz entity classes * @ param entity classes * @ entity classes instantiated by param model * @ return entities Class collection * / public static List castEntity (List list Class clazz, Object model) {List returnList = new ArrayList () If (list.isEmpty ()) return returnList; Object [] co = list.get (0); List attributeInfoList = getFiledsInfo (model); Class [] c2 = new Class [attributeInfoList.size ()]; if (attributeInfoList.size ()! = co.length) {return returnList;} for (int I = 0; I

< attributeInfoList.size(); i++) { c2[i] = (Class) attributeInfoList.get(i).get("type"); } try { for (Object[] o : list) { Constructor constructor = clazz.getConstructor(c2); returnList.add(constructor.newInstance(o)); } } catch (Exception ex) { log.error("实体数据转化为实体类发生异常：异常信息：{}", ex.getMessage()); return returnList; } return returnList; } private static Object getFieldValueByName(String fieldName, Object modle) { try { String firstLetter = fieldName.substring(0, 1).toUpperCase(); String getter = "get" + firstLetter + fieldName.substring(1); Method method = modle.getClass().getMethod(getter, new Class[]{}); Object value = method.invoke(modle, new Object[]{}); return value; } catch (Exception e) { return null; } } private static List getFiledsInfo(Object model) { Field[] fields = model.getClass().getDeclaredFields(); List list = new ArrayList(fields.length); Map infoMap = null; for (int i = 0; i < fields.length; i++) { infoMap = new HashMap(3); infoMap.put("type", fields[i].getType()); infoMap.put("name", fields[i].getName()); infoMap.put("value", getFieldValueByName(fields[i].getName(), model)); list.add(infoMap); } return list; } } 使用原生sql查询： /** * 根据公司名称查询岗位 * @param name 公司名称 * @return List */ @Query(value = "select id, position, salary, people, experience, address, update_time from employment_position where company_name = ?1 and is_delete is false ORDER BY sort asc", nativeQuery = true) List findByCompanyName(String name); 使用类型转换： @Override public List findByCompanyName(String name) { List objects = employmentPositionRepository.findByCompanyName(name); return EntityUtils.castEntity(objects, EmploymentPositionVO.class, new EmploymentPositionVO()); } VO类如下： import lombok.Data; import java.math.BigInteger;import java.sql.Timestamp; /** * @website https://el-admin.vip * @description / * @author budezhenjia * @date 2021-02-08 **/@Datapublic class EmploymentPositionVO { /** ID */ private BigInteger id; /** 岗位名称 */ private String position; /** 月薪 */ private String salary; /** 人数 */ private Integer people; /** 工作经验 */ private String experience; /** 工作地点 */ private String address; /** 更新时间 */ private Timestamp updateTime; public EmploymentPositionVO(BigInteger id, String position, String salary, Integer people, String experience, String address, Timestamp updateTime) { this.id = id; this.position = position; this.salary = salary; this.people = people; this.experience = experience; this.address = address; this.updateTime = updateTime; } public EmploymentPositionVO() { }} 注意！ 查询sql语句所查询出来的字段应与VO类中属性顺序一致，类型也需要一致！！ 例如ID这个字段MySQL中类型为bigint，VO类中的类型为bigInteger dto,vo,po,bo等实体转换工具类 3层开发以及不是多么新颖的开发思想了，但是呢，苦于开发的程序猿们，经常会被各个实例之间的转换弄得晕头转向，尤其是转换的次数多了，一下就蒙了，不知道转到哪里去了，博主也有这种困难，于是在网上到处找，找到了一些方法，并结合自身的开发使用，填补一些坑，希望对大家有所帮助！ 下面宣布这次的主角：dozer 他是谁，一看英文名就不懂吧，其实他是一个大家都知道的一个角色，spring里面他可是家喻户晓的一个主角，没错就是beanUtils（其实，就是他的替身！）主要作用就是用来复制 JavaBean 属性的类库，什么叫复制，没错，就一模一样的再来一份，但是这样有一点点小小的区别，那就是，在使用的时候，需要指定一个"容器"（瞎说的，就是一个映射接受对象，也可以叫做目标）来存放，不然，复制到哪去，是不是。 这个时候呀，就有一个经纪人的出现，需要通过"经纪人"去代理复制，才能叫这个替身出来呀（专业替身30年，必须要有经纪人） net.sf.dozer dozer 5.5.1 好了，经纪人的名片已经发出，这个时候，找到剧组，咱们看看这个替身能不能胜任，能应用在哪些剧组，哪些场景！ 第一种场景，完全一样：（咦，度一样了，那肯定好弄，又看不出来区别） 在各个实体是一样的情况下，是很容易的，直接上不就行啦，也不用做啥处理是不是： 直接是用原始替身（API方法） Mapper mapper = new DozerBeanMapper();DestinationObject destObject = mapper.map(sourceObject, DestinationObject.class); 嘿嘿，换一下衣服，直接OK了（也就是使用mapper转换复制） 第二种场景，完全不一样： 求乞，完全不一样，这咋的弄呀，肯定得换替身，是不是！最起码找个相似的嘛（不用担心，咱们有化妆师呀，化妆走起！） @Datapublic class UserVo{ @Mapping("userName") private String name; @Mapping("password") private String pwd;} 看一下，是不是这个东西，好眼熟，没错，是咱们的vo @Data@TableName("user")public class UserEntity implements Serializable { @ApiModelProperty(value = "id") @TableId(value = "id", type = IdType.INPUT) private String id; @ApiModelProperty(value = "用户名") @Mapping("name") private String userName; @ApiModelProperty(value = "密码") @Mapping("pwd") private String password; @ApiModelProperty(value = "登录名") private String loginName; @ApiModelProperty(value = "创建时间") private Date createTime; @ApiModelProperty(value = "修改时间") private Date updateTime; @ApiModelProperty(value = "版本号") private Integer version; @ApiModelProperty(value = "作废标记") private Integer deleted;} 这个呢，是咱们的实体对象（也就是数据库对象了） 看一下，是不是发小完全不一样呀！ 这里呢，@Mappin充当了化妆品的角色，将每一个不同的细节进行遮盖，使其成为和原来的实例一模一样（也就是做了映射了） @Mapping("userName") private String name; 上面就是一个化妆处理，将name映射为userName 每一个地方处理完成后，直接上剧组，看看能不能不被发现 /** * 转换实体为另一个指定的实体 * 任意一个参数为NULL时 会抛出NPE * * @param source 源实体 不能为NULL * @param clazz 目标实体 不能为NULL * @param 泛型 * @return 转换后的结果 */ @NonNull public static T convert(@NonNull Object source, @NonNull Class clazz) { return dozerMapper.map(source, clazz); } 实例： UserEntity userEntity = userMapper.selectOne(wrapper); UserVo convert = null; if(userEntity != null){ convert = Dozer.convert(userEntity, UserVo.class); } 没错，这样就完成转换替身的操作了，结果是可以映射上的，各位可以试试哦！ 第三种场景，一堆的不相同的替身（好难呀，一堆的不一样，不能找几个差不多的吗？） 针对于这种一堆的不一样的替身，dozer也有办法，通过JAVA8的stream流来进行化妆（化妆师牛，只能这么说） /** * 转换List实体为另一个指定的实体 * source如果为NULL 会使用空集合 * 在目标实体为NULL时 会抛出NPE * * @param source 源集合 可以为NULL * @param clazz 目标实体 不能为NULL * @param 泛型 * @return 转换后的结果 */ @Nullable public static List convert(@Nullable List source, @NonNull Class clazz) { return Optional.ofNullable(source) .orElse(Collections.emptyList()) .stream() .map(bean ->

DozerMapper.map (bean, clazz). Collectors.toList ();}

See, as soon as you do this, you OK. Hey, did you find out where the makeup artist dozerMapper came from (such an awesome makeup artist, call several makeup shops to open)? the blogger told you that the more makeup artists are, the better (as we all know, the same object, too much waste of space). You just need to establish an overall unique one, and the blogger will show you around the dressing room and understand it (tools are here).

Package cn.yichehuoban.ycbb.platform.util.beanutils;import org.dozer.Mapper;import org.springframework.lang.NonNull;import org.springframework.lang.Nullable;import org.springframework.stereotype.Component;import java.util.Collections;import java.util.List;import java.util.Optional;import java.util.stream.Collectors; @ Componentpublic class Dozer {/ * the core mapper object of the dozer transformation * / public static final Mapper dozerMapper = new org.dozer.DozerBeanMapper () / * convert entity to another specified entity * if any parameter is NULL, NPE * * @ param source source entity cannot be NULL * @ param clazz target entity cannot be NULL * @ param generic * @ return converted result * / @ NonNull public static T convert (@ NonNull Object source) @ NonNull Class clazz) {return dozerMapper.map (source, clazz) } / * convert List entity to another specified entity * source will use an empty collection if it is NULL * if the target entity is NULL, it will throw NPE * * @ param source source collection can be NULL * @ param clazz target entity cannot be NULL * @ param generic * @ return converted result * / @ Nullable public static List convert (@ Nullable List source @ NonNull Class clazz) {return Optional.ofNullable (source) .orElse (Collections.emptyList ()) .stream () .map (bean-> dozerMapper.map (bean, clazz)) .destroy (Collectors.toList ()) }}

Let's take a look at our doubles.

Datapublic class UserVo {@ Mapping ("userName") private String name; @ Mapping ("password") private String pwd; private String loginName; private Integer version; private Integer deleted; private String id;}

The same place is mapped directly, and the @ Mapping annotation is used in different places. Just fill in the field name of the specified object in the source.

The above is all the content of the article "how to use JPA to customize VO type conversion". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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