java - RESTful 服务 : Unable to return array of object using json

Question

此样本是从通过 Google 找到的众多样本之一中提取的。应用程序返回 3 个对象，但所有属性均为 NULL。

以下是 Controller 对象。

import java.net.URI;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.support.ServletUriComponentsBuilder;

@RestController
@RequestMapping(path = "/employees")
public class EmployeeController 
{
    @Autowired
    private EmployeeDAO employeeDao;

    @GetMapping(path="/", produces = "application/json")
    public Employees getEmployees() 
    {
        return employeeDao.getAllEmployees();
    }

    @PostMapping(path= "/", consumes = "application/json", produces = "application/json")
    public ResponseEntity<Object> addEmployee(@RequestBody Employee employee) 
    {
        Integer id = employeeDao.getAllEmployees().getEmployeeList().size() + 1;
        employee.setId(id);

        employeeDao.addEmployee(employee);

        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
                                    .path("/{id}")
                                    .buildAndExpand(employee.getId())
                                    .toUri();

        return ResponseEntity.created(location).build();
    }
}

这是通过 getEmployees 调用返回的Employees 对象。

import java.util.ArrayList;
import java.util.List;

public class Employees 
{
    private List<Employee> employeeList;

    public List<Employee> getEmployeeList() {
        if(employeeList == null) {
            employeeList = new ArrayList<>();
        }
        return employeeList;
    }

    public void setEmployeeList(List<Employee> employeeList) {
        this.employeeList = employeeList;
    }
}

如果您需要它，这里是 DAO。

import org.springframework.stereotype.Repository;

@Repository
public class EmployeeDAO 
{
    private static Employees list = new Employees();

    static
    {
        list.getEmployeeList().add(new Employee(11, "Lokesh", "Gupta", "howtodoinjava@gmail.com"));
        list.getEmployeeList().add(new Employee(22, "Alex", "Kolenchiskey", "abc@gmail.com"));
        list.getEmployeeList().add(new Employee(33, "David", "Kameron", "titanic@gmail.com"));
    }

    public Employees getAllEmployees() 
    {
        return list;
    }

    public void addEmployee(Employee employee) {
        list.getEmployeeList().add(employee);
    }
}

根据要求，这里是 Employee 类。

import javax.annotation.ManagedBean;

import org.springframework.web.context.annotation.ApplicationScope;

import lombok.Data;
import lombok.Getter;
import lombok.Setter;

//@ManagedBean
//@ApplicationScope
//@Data

public class Employee {


    public Employee() {

    }
    public Employee(Integer id, String firstName, String lastName, String email) {
        super();
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    @Setter  @Getter  private Integer id;
    private String firstName;
    private String lastName;
    private String email;

    //Getters and setters

    @Override
    public String toString() {
        return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", email=" + email + "]";
    }
}

这是部分客户端代码......

    private static void getEmployees() 
    {

        // HttpHeaders
        HttpHeaders headers = new HttpHeaders();

        headers.setAccept(Arrays.asList(new MediaType[] { MediaType.APPLICATION_JSON }));
        // Request to return JSON format
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.set("my_other_key", "my_other_value");

        // HttpEntity<String>: To get result as String.
        HttpEntity<String> entity = new HttpEntity<String>(headers);

        // RestTemplate
        RestTemplate restTemplate = new RestTemplate();

        // Send request with GET method, and Headers.
        ///This works but only prints IDs.        
        ResponseEntity<String> response = restTemplate.exchange(URL_EMPLOYEES, HttpMethod.GET, entity, String.class);
        String result = response.getBody();
        System.out.println(result);

        HttpEntity<Employees> entity2 = new HttpEntity<Employees>(headers);
      ResponseEntity<Employees> eResponse = restTemplate.exchange(URL_EMPLOYEES, HttpMethod.GET, entity2, Employees.class);
      List <Employee> eList = eResponse.getBody().getEmployeeList();
      for (Employee e : eList)
      {
          System.out.println(e.toString());
      }
   }

根据上面的内容，以下调用有效并打印出 3 个 ID。

    ResponseEntity<String> response = restTemplate.exchange(URL_EMPLOYEES, HttpMethod.GET, entity, String.class);
    String result = response.getBody();
    System.out.println(result);

返回 ID 后，下一步是使用下一组调用打印出每个员工的所有属性。

  ResponseEntity<Employees> eResponse = restTemplate.exchange(URL_EMPLOYEES, HttpMethod.GET, entity, Employees.class);
  List <Employee> eList = eResponse.getBody().getEmployeeList();
  for (Employee e : eList)
  {
      System.out.println(e.toString());
  }

我在执行 LIST 调用的行上放置了一个断点，并验证了 eResponse 对象在列表中有 3 个项目，但所有 3 个项目均显示其关联属性均为 NULL。

由于我确认调用似乎在第一次调用中返回了 ID，因此第二次调用缺少什么命令或设置来允许返回完整的对象？

Answer 1

我认为你应该删除 super();在构造函数中。我们用它来访问父类(super class)的成员。您的 Employee 类没有父类。