在数据库中获取从 postman JSON 格式发送的 null 值

问：

我必须使用 servlet 创建一个 API 的 crud 应用程序，并从邮递员那里测试该 API，所以我开始做 crud 应用程序，我首先创建了插入数据 API，它将通过邮递员从 JSON 中获取数据，并且来自 JSON 的数据将来自并存储在数据库中。所以我在 postman 中提供了数据，它也给了我 200 OK 信号，并且还显示数据添加成功消息，但是当我转到 pgadmin 并看到所有行数据都以 null 形式保存时，所以我检查了 servlet，我们在下面有方法，我已经写了 println 行，该行将显示我从 JSON 获取的数据， 所以数据也给了我错误。request.getparameter

package com.conn;



import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MyConnection {
    
    
    public static Connection getConnection() {
        String URL = "jdbc:postgresql://localhost:5432/sample";
        String USERNAME = "postgres";
        String PASSWORD = "Rhythm";
        Connection connection = null;
        
            try {
                Class.forName("org.postgresql.Driver");
                connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
                System.out.println("Connected to the database successfully.");
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
        return connection;
    }
    
    /*
     * public static void main(String[] args) { getConnection(); }
     */
}

package com.controller;

import java.io.IOException;

import java.io.PrintWriter;
import java.sql.Connection;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.conn.MyConnection;
import com.dao.EmployeeDao;
import com.model.Employee;

/**
 * Servlet implementation class SaveData
 */
@WebServlet("/SaveData")
public class SaveData extends HttpServlet {
    //private static final long serialVersionUID = 1L;
    private EmployeeDao employeeDao;
    Connection connection;
    
    /**
     * @see HttpServlet#HttpServlet()
     */
    
    // Database credentials
    @Override
    public void init() throws ServletException {
        super.init();
        connection = MyConnection.getConnection();
        employeeDao = new EmployeeDao(connection);
    }
    
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //response.getWriter().append("Served at: ").append(request.getContextPath());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
        int i=0;
        
        String name = request.getParameter("name");
        String email = request.getParameter("email");
        String mobile_number = request.getParameter("mobile_number");
        int department_id = Integer.parseInt(request.getParameter("department_id"));
        int designation_id= Integer.parseInt(request.getParameter("designation_id"));
        String gender = request.getParameter("gender");
        boolean age = request.getParameter("age") != null;
        
        // Validation logic can be added here
        Employee emp = new Employee(name, email, Integer.parseInt(mobile_number), department_id, designation_id, gender, age);
        // Insert employee into the database
        PrintWriter out=response.getWriter();
        
        out.println("name"+emp.getName());
        out.println("email"+emp.getEmail());
        out.println("mobile_number"+emp.getMobile_number());
        out.println("department_id"+emp.getDepartment_id());
        out.println("deignation_id"+emp.getDesignation_id());
        out.println("gender"+emp.getGender());
        out.println("age_above_18"+emp.isAge_above_18());
        
        List<Employee> lst=new ArrayList<Employee>();
        lst.add(emp);
        
       i= employeeDao.create(lst);
       response.setStatus(HttpServletResponse.SC_CREATED);
       response.getWriter().write("Employee added successfully");
            if(i>0)
            {
                System.out.println("create employee...");
            }
            else {
                System.out.println("error ocuur");
            }
    }
    
    }