你的控制器不应该返回entities（带有注解@Entity的类）。最好的做法是创建另一个具有相同属性的单独类。这段代码有一点重复，但它保持了所有层的干净。我还建议使用@Service。

public class RoomDTO { 
       private String name;
       private List<TeamDTO> teams = new ArrayList<>();   

       public RoomDTO() { 
       }
        
       public RoomDTO(Room room) {
            this.name = room.name;
            for(Team team : room.getTeams()) {
                 TeamDTO teamDTO = new TeamDTO();
                 teamDTO.setName(team.getName);
                 teams.add(teamDTO);
            }
        }
   }


   public class TeamDTO { 
       List<RoomDTO> rooms = new ArrayList();

       public TeamDTO() {
       }

       public TeamDTO(Team team) {
            this.name = team.name;
            for(Room room : team.getRooms()) {
                 RoomDTO roomDTO = new RoomDTO();
                 roomDTO.setName(team.getName);
                 rooms.add(roomDTO);
            }
        }
        
   }

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控制器应该返回这个

@GetMapping
public Iterable<TeamDTO> getAllRoomsOfTeam() {
final long exampleId = 1;
final var team = teamRepository.findById(exampleId);

TeamDTO teamDTO = new TeamDTO(team);

return ResponseEntity.ok(teamDTO);

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}
How to use DTOs in the Controller, Service and Repository pattern

目前，在您的类中存在循环依赖，这导致在将对象转换为JSON时出现问题。请在Team类中的rooms变量上添加@JsonIgnore注解，如以下示例所示：

import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity
public class Team {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @ManyToMany
    @JoinTable(name = "teams_rooms",
        joinColumns = @JoinColumn(name= "team_id"),
        inverseJoinColumns = @JoinColumn(name = "room_id"))
    @JsonIgnore
    private Set<Room> rooms;

}

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如果你需要一个双向转换的解决方案，那么你可以使用JsonView注解。
首先，您需要为Team和Room创建JSON视图配置文件，如以下示例所示：

public class JsonViewProfiles
{
    /**
     * This profile will be used while converting Team object to JSON
     */
    public static class Team {}

    /**
     * This profile will be used while converting Room object to JSON
     */
    public static class Room {}
}

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在实体中使用上面创建的JSON视图配置文件，如下面的示例所示：

public class Room {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @JsonView({ JsonViewProfiles.Team.class, JsonViewProfiles.Room.class })
    private long id;

    @JsonView(JsonViewProfiles.Room.class)
    @ManyToMany(mappedBy = "rooms")
    private Set<Team> teams;
}

public class Team {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @JsonView({JsonViewProfiles.Team.class, JsonViewProfiles.Room.class})
    private long id;

    @ManyToMany
    @JoinTable(name = "teams_rooms",
        joinColumns = @JoinColumn(name= "team_id"),
        inverseJoinColumns = @JoinColumn(name = "room_id"))
    @JsonView(JsonViewProfiles.Team.class)
    private Set<Room> rooms;
}

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在将对象转换为JSON时，请使用以下示例中所示的配置文件：

@GetMapping
public String getAllRoomsOfTeam() {
    final long exampleId = 1; //This is just a placeholder. The id will be passed as a parameter.

    final Team team = teamRepository.findById(exampleId);

    String result = new ObjectMapper().writerWithView(JsonViewProfiles.Team.class)
                .writeValueAsString(team);

    return result;
}

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