tasks表对应的Entity
@Entity
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "tasks")
@Data
public class Tasks extends BaseEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int taskId;
private Integer websiteId;
private String status;
private String lastOperator;
private String lastOperationTime;
private String jobId;
private int retryTimes;
}websites表对应的Entity
@Entity
@Table(name = "websites")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Websites extends BaseEntity{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int websiteId;
private String country;
private String websiteName;
private String baseUrl;
private String smartphoneUrl;
private String tabletUrl;
private String smartdeviceUrl;
private String websiteCategory;
private String webtypeRefreshRate;
private String urlRefreshRate;
private String configTime;
private String configDesc;
}自定义对象
@Data
@NoArgsConstructor
@AllArgsConstructor
public class CustomizedDto implements Serializable {
private static final long serialVersionUID = -7242005560621561106L;
private String country;
private String websiteName;
private String baseUrl;
private String status;
}方法一、简单查询直接new对象
使用hql，将结果返回到new出来的自定义对象中，注意，自定义对象中要有对应的构造函数。
@Query(value = "select new com.bigdata.mrcrawler.dto.CustomizedDto(w.country,w.websiteName,w.baseUrl,t.status) " +
"from Websites w join Tasks t on w.id=t.websiteId " +
"where t.status=?1")
List<CustomizedDto> getByStatus1(String status);但是这个方法只使用于简单的查询语句，如果遇到复杂查询需要使用原生SQL（即nativeQuery=true）时， 此方法不适用，会抛出如下异常。
@Query(value = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status " +
"from websites w join tasks t on w.website_id=t.website_id " +
"where t.status=?1",nativeQuery = true)
List<CustomizedDto> getByStatus2(String status);No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [com.bigdata.mrcrawler.dto.CustomizedDto]
方法二、Service层使用EntityManager
直接在Service层使用EntityManager进行查询，可以自由组装各种复杂sql。
public List<CustomizedDto> t(String param) {
String sql = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status " +
"from websites w join tasks t on w.website_id=t.website_id " +
"where t.status='" + param + "'";
List<CustomizedDto> res = entityManager.createNativeQuery(sql).getResultList();
return res;
}但是会有sql注入问题，例如：param传入Running' or 1=1 --\t 上述查询会将查询整个数据表。解决方法如下，使用预编译防止sql注入问题。
public List<CustomizedDto> t(String param) {
String sql = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status " +
"from websites w join tasks t on w.website_id=t.website_id " +
"where t.status=:param" ;
Query nativeQuery = entityManager.createNativeQuery(sql);
nativeQuery.setParameter("param", param);
List<CustomizedDto> res = nativeQuery.getResultList();
return res;
}然而，个人很不喜欢这种代码中嵌入大片大片sql的写法，排查问题的时候看得头疼（别问，问就是被坑过/捂脸.jpg/）。所以方法二即便可行，我私心还是不想推荐。
方法三、Dao层使用Map接收自定义对象
使用List<Map> 接收返回结果，无论是原生sql还是hql都支持，当然也支持分页，只需要把返回对象改为Page<Map>即可，其他操作与普通分页没有差别。
@Query(value = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status " +
"from websites w join tasks t on w.website_id=t.website_id " +
"where t.status=?1",nativeQuery = true)
List<Map> getByStatus3(String status);Service层也需要用List<Map>进行接收。
public List<Map> t(String param) {
return testRepository.getByStatus3(param);
}如果后续还有其他操作，还是需要转成自定义对象怎么办，毕竟Map操作起来挺麻烦的。可以用如下解决方案，先用Object进行接收，然后强转成自定义对象List。
public List<CustomizedDto> t(String param) {
Object data = testRepository.getByStatus3(param);
return (List<CustomizedDto>)data;
}强转需要注意自定义对象和数据库中字段类型的强一致性，如数据库中datetime类型，自定义对象对应的字段必须是Date，不能是String，否则转换的时候会有问题，数据会丢失。
总结
到此这篇关于Spring Data Jpa返回自定义对象的3种方法的文章就介绍到这了,更多相关Spring Data Jpa返回自定义对象内容请搜索编程网以前的文章或继续浏览下面的相关文章希望大家以后多多支持编程网！
