如何在 Java Spring Boot 中创建列表列表？

Question

我是 java 和 springboot 的新手。我正在尝试使用 springboot 创建一个 CRUD 应用程序。 我正在使用 MySQL 来存储数据。

员工模型 -

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "employees")
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email_id")
    private String emailId;

    public Employee() {
    }

    public Employee(String firstName, String lastName, String emailId) {
        super();
        this.firstName = firstName;
        this.lastName = lastName;
        this.emailId = emailId;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmailId() {
        return emailId;
    }

    public void setEmailId(String emailId) {
        this.emailId = emailId;
    }

}

员工资料库 -

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import com.raksh.springboot.model.Employee;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long> {

}

员工控制器 -

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.raksh.springboot.model.Employee;
import com.raksh.springboot.repository.EmployeeRepository;

@CrossOrigin(origins = "http://localhost:3000/")
@RestController
@RequestMapping("/api/v1/")
public class EmployeeController {

    @Autowired
    private EmployeeRepository employeeRepository;

    // get all employees
    @GetMapping("/employees")
    public List<Employee> getAllEmployees(){
        return employeeRepository.findAll();
    }

}

上面的控制器以 JSON 对象数组形式给我结果，如下所示

[
  {
    "id": 1,
    "firstName": "Tony",
    "lastName": "Stark",
    "emailId": "tony@gmail.com"
  },
  {
    "id": 2,
    "firstName": "Thor",
    "lastName": "Odinson",
    "emailId": "thor@asgard.com"
  }
]

但我需要以下表格的回复

{
    total_items: 100,
    has_more: true,
    employees : {
        1 : {
            "id": 1,
            "firstName": "Raksh",
            "lastName": "Sindhe",
            "emailId": "raksh@gmail.com"
        },
        2: {
            "id": 2,
            "firstName": "Thor",
            "lastName": "Odinson",
            "emailId": "thor@asgard.com"
        }
    }
}

非常感谢您的帮助。

Answer 1

您应该创建 EmployeeResponse 模型（根据需要更改名称）。 添加您需要的其他字段。 total_items 可以使用 list.size() 计算。 对于另一个字段，我会在数据库中添加一个额外的查询来计算行数，例如按 id 列。 比较是否超过 100 并将该字段设置为 true。

您可以在此处查看示例：Does Spring Data JPA have any way to count entites using method name resolving?

如果在“findAll”方法中您没有限制为 100 行，并且您实际上获取了所有员工，然后移动了除 100 之外的所有员工，您可以设置此字段而无需额外的计数查询。

Answer 2

只需将结果封装在 DTO 类中，并与响应一起传回即可。

total_items - 可以通过存储库返回的列表的大小来推断。

has_more - 如果您将findAll() 与存储库调用一起使用，那么您将获得数据库中的所有员工。否则，您可能必须在存储库中引入分页。

employees - 在Map 中包含员工

响应DTO

public class ResponseDTO {

    private int total_items;

    private boolean has_more;

    private Map<Integer, Employee> employees;

    public ResponseDTO(int totalItems, boolean hasMore, Map<Integer, Employee> employees) {
        this.total_items=totalItems;
        this.has_more=hasMore;
        this.employees=employees;
    }

    //constructors, getters, and setters
}

员工控制器

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.raksh.springboot.model.Employee;
import com.raksh.springboot.repository.EmployeeRepository;

@CrossOrigin(origins = "http://localhost:3000/")
@RestController
@RequestMapping("/api/v1/")
public class EmployeeController {

    @Autowired
    private EmployeeRepository employeeRepository;

    // get all employees
    @GetMapping("/employees")
    public List<Employee> getAllEmployees(){

        Pageable employeePage = PageRequest.of(0, 100); //so you expect first 100 slice from all the employees in the DB.
        Page<Employee> employees = employeeRepository.findAll(employeePage);
        Map<Integer, Employee> employeeMap = getEmployeeMap(employees.getContent());
        
        return new ResponseDTO(employees.getNumberOfElements(),employees.hasNext(),employeeMap );
    }

    private Map<Integer, Employee> getEmployeeMap(List<Employee> empoyees){

        if(employees!=null && !empoyees.isEmpty){
            Map<Integer, Employee> employeeMap = new HashMap<>();
            for(Employee emp:empoyees){
                employeeMap.put(emp.getId(),emp);
            }
            return employeeMap;
        }
        return null;
    }

}