如何在Java Springboot中创建列表列表？

Question

我不熟悉java和springboot。我正在尝试使用springboot创建一个CRUD应用程序。我使用MySQL存储数据。

员工模式-

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;
    }

}

员工资源库-

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> {

}

员工控制员-

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();
    }

}

上面的控制器在JSON对象数组表单中给出了结果，如下所示

[
  {
    "id": 1,
    "firstName": "Tony",
    "lastName": "Stark",
    "emailId": "[e-mail]"
  },
  {
    "id": 2,
    "firstName": "Thor",
    "lastName": "Odinson",
    "emailId": "[e-mail]"
  }
]

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": "[e-mail]"
        },
        2: {
            "id": 2,
            "firstName": "Thor",
            "lastName": "Odinson",
            "emailId": "[e-mail]"
        }
    }
}

非常感谢你的帮助。

Answer 1

只需将结果封装在DTO类中，并将其与响应一起传递回来。

total_items-可以通过存储库返回的列表的大小来推断。

has_more-如果你使用findAll（）与仓库调用，那么你会得到DB中的所有员工。否则，您可能必须使用存储库引入分页。

员工-在地图中包含员工

回应

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
}

雇员管制员

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;
    }

}

Answer 2

您应该创建员工响应模型（根据需要更改名称）。添加所需的其他字段。total_items可以用list.size（）计算。对于另一个字段，我将向数据库添加一个额外的查询来计算行数，例如通过id列。比较它是否超过100，并将该字段设置为true。

您可以在这里看到一个例子：Spring Data JPA是否有任何方法可以使用方法名解析来计算实体数？

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