JsonMappingException: Infinite recursion (StackOverflowError) in Spring Boot GET request

Question

I'm using Spring Boot to create a restful API along with JPA. I'm having problems when trying to get results using GET request with ResponseEntity to generate a JSON. Looks like it's returning an infinite JSON..

Code:

    @GetMapping("/machines")
    public ResponseEntity<List<Machine>> getMachines() {
        List<Machine> result = this.machineRepository.findAll();
        return new ResponseEntity<>(result, HttpStatus.OK);

Error:

[nio-8080-exec-1] s.e.ErrorMvcAutoConfiguration$StaticView : Cannot render error page for request [/main/machines] and exception [Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: org.hibernate.collection.internal.PersistentSet[0]->com.main.example.model.SoftwareCode["machines"]->org.hibernate.collection.internal.PersistentSet[0]->com.main.example.model.Machine["softwareCodes"]->org.hibernate.collection.internal.PersistentSet[0]->com.

- Also, here's some background of what I persisted to DB, to give you some context

Machine.java:

@Entity
public class Machine {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;

    private String name;

    @ManyToMany(cascade = {CascadeType.PERSIST,CascadeType.MERGE}, fetch = FetchType.EAGER)
    @JoinTable(
        name = "software_codes",
        joinColumns = @JoinColumn(name = "machine_id"),
        inverseJoinColumns = @JoinColumn(name = "software_id"))
    private Set<SoftwareCode> softwareCodes = new HashSet<>();

    public Machine(String name, Set<SoftwareCode> softwareCodes) {
        this.name = name;
        this.softwareCodes = softwareCodes;
    }

SoftwareCode.java:

@Entity
public class SoftwareCode {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;

    private String code;

    @ManyToMany(mappedBy = "softwareCodes", cascade = {CascadeType.PERSIST,CascadeType.MERGE}, fetch = FetchType.EAGER)
    private Set<Machine> machines;

    public SoftwareCode(String code) {
        this.code = code;
    }

My approach to persist to DB:

Set<Machine> machines = new HashSet<>();
Set<SoftwareCode> softwareCodes = new HashSet<>();

SoftwareCode softwareCode = new SoftwareCode("ABC");
SoftwareCode softwareCode2 = new SoftwareCode("XYZ");
softwareCodes.add(softwareCode);
softwareCodes.add(softwareCode2);
Machine machine = new Machine("machine1", softwareCodes);
machines.add(machine);

vehicleRepository.saveAll(machines);