Post request returning java.lang.NullPointerException

Question

I am creating a web app with Spring for the first time.

I have 2 class, machine and status. Each machines got multiples status.

When I created the requests for the machines - no problems. But I am trying to create the request for the status and I can't manage to make the POST request work.

I linked the status with the machine using @ManyToOne but when i am testing to post a status in a machine Spring returns : java.lang.NullPointerException: Cannot invoke "com.example.DCT.repository.MachineRepository.findById(Object)" because "this.machineRepository" is null

@Entity
public class Status {

    @Id
    private Long id;
    private String name;
    private Boolean state;
    @ManyToOne
    private Machine machine;
    
    public Machine getMachine() {
        return machine;
    }


    public void setMachine(Machine machine) {
        this.machine = machine;
    }


    public Status() {
        
    }
    
    
    public Status(Long id, String name, Boolean state,Machine machine){
        this.id = Long.valueOf(id);
        this.name = name;
        this.state = state;
        this.machine = machine;
    }
    
    
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Boolean getState() {
        return state;
    }
    public void setState(Boolean state) {
        this.state = state;
    }

@Service
public class StatusServiceImpl {
    
    StatusRepository statusRepository;

    public List<Status> getAllStatus(Long machineId){
        List<Status> status =new ArrayList<>();
        statusRepository.findByMachineId(machineId)
        .forEach(status::add);
        return status;
    }
    
    public Optional<Status> getStatus(Long statusId) {
        return statusRepository.findById(statusId);
    }
    
    public void addStatus(Status status) {
        statusRepository.save(status);
    }
    
    public void updateStatus(Status status) {
        statusRepository.save(status);
    }
    
    public void deleteStatus(Long id) {
        statusRepository.deleteById(id);
    }
    
 }

@RestController
public class StatusControllerImpl {

    @Autowired
    private StatusServiceImpl statusServiceImpl;
    private MachineRepository machineRepository;
    
    @GetMapping("/machines/{machineId}/status")
    public List<Status> getAllStatus(@PathVariable Long machineId){
        return statusServiceImpl.getAllStatus(machineId);
    }
    
    @GetMapping("/machines/{machineId}/status/{statusId}")
    public Optional<Status> getStatus(@PathVariable Long statusId){
        return statusServiceImpl.getStatus(statusId);
    }
    
    @RequestMapping(method=RequestMethod.POST, value="/machines/{machineId}/status")
    public void addStatus(@RequestBody Status status, @PathVariable Long machineId) {
    
        status.setMachine(machineRepository.findById(machineId).get());
        statusServiceImpl.addStatus(status);
    }
    
    @PutMapping("/machines/{machineId}/status/{statusId}")
    public void updateStatus(@RequestBody Status status,@PathVariable Long statusId, @PathVariable Long machineId) {
        status.setMachine(machineRepository.findById(machineId).get());
        statusServiceImpl.updateStatus(status);
    }
    
    @RequestMapping(method=RequestMethod.DELETE, value="/machines/{machineId}/status/{statusId}")
    public void deleteStatus(@PathVariable Long statusId) {
        statusServiceImpl.deleteStatus(statusId);
    }
}

Thanks to anyone who will try to help me.

This is my first post on stackOverflow I hope I'm not doing mistakes.

you never assign a value to the machineRepository variable in your StatusControllerImpl class, maybe you have to write @Autowired above "private MachineRepository machineRepository;" too (?) — JavaMan
– JavaMan, Commented Feb 21, 2021 at 14:11

eHayik · Accepted Answer · 2021-02-21 14:12:10Z

1

I think it's due to private MachineRepository machineRepository; doesn't have the @Autowired annotation therefore the MachineRepository instance managed by Spring is not injected and you got the NullPointerException.

answered Feb 21, 2021 at 14:12

eHayik

3,3021 gold badge26 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Hugo Delautre Over a year ago

Thanks that was the problem thank you for helping me!

Abdalrhman Alkraien · Accepted Answer · 2021-02-21 14:14:03Z

1

@Autowired
private StatusServiceImpl statusServiceImpl;
@Autowired
private MachineRepository machineRepository;    

@RequestMapping(method=RequestMethod.POST, 
    value="/machines/{machineId}/status")
    public void addStatus(@RequestBody Status status, @PathVariable Long machineId) 
    {
    if(machineRepository.findById(machineId).get()!=null)
       status.setMachine(machineRepository.findById(machineId).get());
       statusServiceImpl.addStatus(status);
    }

answered Feb 21, 2021 at 14:14

Abdalrhman Alkraien

8262 gold badges9 silver badges27 bronze badges

1 Comment

Hugo Delautre Over a year ago

Thanks for the help, Autowired was the problem.

Collectives™ on Stack Overflow

Post request returning java.lang.NullPointerException

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related