JPA OneToMany，如何在控制台或webapp中打印时忽略字段ManyToOne

一卷旌收千骑虏，万全身出百重围。这篇文章主要讲述JPA OneToMany，如何在控制台或webapp中打印时忽略字段ManyToOne相关的知识，希望能为你提供帮助。
我有2个表：流派（genre_id，genre_name）和电影（movie_id，movie_name，movie_score，genre_id）。 genre_id_fk来自类型中引用genre_id的电影。

@Entity @Table(name = "genres", schema = "test") public class Genre {@Id @Column(name = "genre_id") private int id; @Column(name = "genre_name") private String name; @OneToMany(mappedBy = "genre", fetch = FetchType.LAZY) private List< Movie> movies = new ArrayList< > (); }

第二个电影实体

@Entity @Table(name = "movies", schema = "test") public class Movie {@Id @GeneratedValue @Column(name = "movie_id") private int id; @Column(name = "movie_name") private String name; @Column(name = "movie_score") private double score; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "genre_id") private Genre genre; }

当我尝试使用此代码在控制台中打印它时：

public static void main(String[] args) { EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu"); EntityManager em = emf.createEntityManager(); Genre genre = em.find(Genre.class, 1); System.out.println(genre); }

接收Exception in thread "main" java.lang.StackOverflowError只删除电影类字段“genres”中的toString（）可以修复它。但是有可能避免它吗？和春季启动应用程序相同的问题

@RestController public class GenreController {@Autowired private GenreService genreService; @RequestMapping("/test/{id}") public List< Genre> getGenreInfo(@PathVariable int id){ return genreService.getGenreFilms(id); } }

在这里服务

@Service public class GenreService {public List< Genre> getGenreFilms(int id){ EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu"); EntityManager em = emf.createEntityManager(); List< Genre> genres = new ArrayList< > (); Genre genre = em.find(Genre.class, id); genres.add(genre); return genres; } }

【JPA OneToMany，如何在控制台或webapp中打印时忽略字段ManyToOne】并收到这样的问题：[{“id”：1，“name”：“Thriller”，“movies”：[{“id”：1，“name”：“Any，你还好吗？”，“得分” ：5.45，“genre”：{“id”：1，“name”：“Thriller”，“movies”：[{“id”：1，“name”：“Any，你还好吗？”，“得分” ：5.45，“genre”：{“id”：1，“name”：“Thriller”，“movies”：[{“id”：1，“name”：“Any，你还好吗？”，“得分” ：5.45，“流派”：......和无限，有异常。控制台我可以通过忽略toString（）方法中的字段来修复。但是如何在webapplication中解决这个问题呢？
这里是控制台打印时的hibernate调试日志

22:15:37.154 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Resolving associations for [com.company.Genre#1] 22:15:37.164 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done materializing entity [com.company.Genre#1] 22:15:37.164 [main] DEBUG org.hibernate.resource.jdbc.internal.ResourceRegistryStandardImpl - HHH000387: ResultSet's statement was not registered 22:15:37.165 [main] DEBUG org.hibernate.loader.entity.plan.AbstractLoadPlanBasedEntityLoader - Done entity load : com.company.Genre#1 22:15:37.165 [main] DEBUG org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl - Initiating JDBC connection release from afterTransaction 22:15:37.167 [main] DEBUG org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer - Loading collection: [com.company.Genre.movies#1] 22:15:37.167 [main] DEBUG org.hibernate.SQL - select movies0_.genre_id as genre_id4_1_0_, movies0_.movie_id as movie_id1_1_0_, movies0_.movie_id as movie_id1_1_1_, movies0_.genre_id as genre_id4_1_1_, movies0_.movie_name as movie_na2_1_1_, movies0_.movie_score as movie_sc3_1_1_ from test.movies movies0_ where movies0_.genre_id=? Hibernate: select movies0_.genre_id as genre_id4_1_0_, movies0_.movie_id as movie_id1_1_0_, movies0_.movie_id as movie_id1_1_1_, movies0_.genre_id as genre_id4_1_1_, movies0_.movie_name as movie_na2_1_1_, movies0_.movie_score as movie_sc3_1_1_ from test.movies movies0_ where movies0_.genre_id=? 22:15:37.168 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - Preparing collection intializer : [com.company.Genre.movies#1] 22:15:37.170 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - Starting ResultSet row #0 22:15:37.171 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm pl - Found row of collection: [com.company.Genre.movies#1] 22:15:37.171 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - Starting ResultSet row #1 22:15:37.172 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm pl - Found row of collection: [com.company.Genre.movies#1] 22:15:37.172 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - Starting ResultSet row #2 22:15:37.172 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm pl - Found row of collection: [com.company.Genre.movies#1] 22:15:37.172 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Resolving associations for [com.company.Movie#1] 22:15:37.172 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done materializing entity [com.company.Movie#1] 22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Resolving associations for [com.company.Movie#2] 22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done materializing entity [com.company.Movie#2] 22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Resolving associations for [com.company.Movie#3] 22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done materializing entity [com.company.Movie#3] 22:15:37.173 [main] DEBUG org.hibernate.engine.loading.internal.CollectionLoadContext - 1 collections were found in result set for role: com.company.Genre.movies 22:15:37.173 [main] DEBUG org.hibernate.engine.loading.internal.CollectionLoadContext - Collection fully initialized: [com.company.Genre.movies#1] 22:15:37.173 [main] DEBUG org.hibernate.engine.loading.internal.CollectionLoadContext - 1 collections initialized for role: com.company.Genre.movies 22:15:37.173 [main] DEBUG org.hibernate.resource.jdbc.internal.ResourceRegistryStandardImpl - HHH000387: ResultSet's statement was not registered 22:15:37.173 [main] DEBUG org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer - Done loading collection Exception in thread "main" java.lang.StackOverflowError

告诉我我在哪里做错了以及如何解决或谷歌这个问题？只是不能通过localhost：8080 / genre / id打印这个对象？制作特定的印刷品或什么？
答案当你尝试toString你的Genre实体时，你似乎有无限的递归。您的代码首先按id加载您的Genre实体，然后调用Genre.toString()。因为你与@OneToManys有Movie关系，所以lazy loads列表然后为每个与该类型相关的电影调用Movie.toString()。然后，对于每部电影，你都会与流派有@ManyToOne关系。这就是问题所在。它将再次为列表中的每部电影调用Genre.toString()。
可能的解决方案

如果您只想在控制台中打印它，请不要在Genre.toString()中包含电影列表
如果您正在使用杰克逊，请将@JsonBackReference添加到您在@ManyToOne的Movie关系中，这样杰克逊在映射到Json Annotation documentation here时会忽略它
如果使用DTO，请不要在DTO中包含Movie属性。

希望这可以帮助。