弹簧架控制器

Question

I can't make spring serialize the response when results is array/list . So when I call clients from RestController it does return [{},{},{}] , instead of real objects, all other methods works just fine.

package com.test.Domain.Client;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;    
import javax.persistence.Table;
import java.util.UUID;

@Entity
@Table(name = "client")
public class Client {

    @Column(name = "client_id")
    @Id
    private UUID clientId;
    @Column(name = "name")
    private String name;

    private Client() {

    }

    private Client(UUID clientId, String name) {

        this.clientId = clientId;
        this.name = name;
    }

    public static Client create(String name)
    {
        return new Client(UUID.randomUUID(), name);
    }
}

---

package com.test.Rest;

import com.test.Domain.Calendar.AppointmentRepository;
import com.test.Domain.Client.Client;
import com.test.Domain.Client.ClientRepository;
import com.test.Domain.Worker.WorkerRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;

@org.springframework.web.bind.annotation.RestController
public class RestController {

    @Autowired
    private ClientRepository clientRepository;
    @Autowired
    private WorkerRepository workerRepository;
    @Autowired
    private AppointmentRepository appointmentRepository;


    @RequestMapping(path = "/client", method = RequestMethod.POST)
    public void registerClient(@RequestParam(name = "name") String name) {
        this.clientRepository.save(Client.create(name));
    }

    @RequestMapping(path = "/clientCount", method = RequestMethod.GET)
    public Long countClient() {
        return this.clientRepository.count();
    }

    @RequestMapping(path = "/clients", method = RequestMethod.GET)
    @ResponseBody
    public List<Client> clients() {
        List<Client> list = new ArrayList<Client>();
        for (Client client : this.clientRepository.findAll()) {
            list.add(client);
        }

        return list;
    }
}

Answer 1

Jackson needs Getter and Setter methods in order to serialize the Client object properly into JSON. Therefore a list of empty objects is returned and the values for the members are missing. Add them to Client and the response should look fine.

Answer 2

Spring applies first registered applicable by response mime-type HttpMessageConverter implementation when serializing the response to /clients call. In your case this is some JSON serializer. As you have no JSON configuration specified on Client class the default POJO serializing approach is used: reflection scanning of object properties. As mentioned earlier your Client class doesn't define any properties (at least getters), so serializer do not detect any.

Please refer to the following article for a more detailed explanation: https://www.javacodegeeks.com/2013/07/spring-mvc-requestbody-and-responsebody-demystified.html

PS Marking method with @ResponseBody in @RestController annotated class is not necessary as itself is a convenience annotation aggregating @Controller and @ResponseBody .