员工管理-登陆及增删改查功能的实现

• 问题

为员工管理系统添加注册和登陆功能，注册时需要进行用户名是否存在的判断，如果存在则出现提示。登陆成功即可对员工信息进行增删改查操作。

• 步骤
  Step 1：创建数据库表
  新建一个登陆表，t_user表

CREATE TABLE `t_user` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `username` varchar(20) NOT NULL,
  `pwd` varchar(30) NOT NULL,
  `name` varchar(50) DEFAULT NULL,
  `gender` char(2) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8;

新建一个员工表t_emp

CREATE TABLE `t_emp` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `name` varchar(8) NOT NULL,
  `salary` float(8,2) DEFAULT NULL,
  `age` int(2) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

step2: 创建一个实体类entity.User类和一个实体类entity.Employee类

package entity;

public class Employee {
   
   
    private int id;
    private String name;
    private float salary;
    private int age;

    @Override
    public String toString(){
        return id+" "+name+" "+salary+" "+age;
    }
    public Employee(){
        super();
    }
    public Employee(int id,String name,float salary,int age){
        super();
        this.id=id;
        this.name=name;
        this.salary=salary;
        this.age=age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public float getSalary() {
        return salary;
    }
    public void setSalary(float salary) {
        this.salary = salary;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

}

entity.User类

package entity;

public class User {
   
   
    private int id;
    private String username;
    private String pwd;
    private String name;
    private String gender;

    @Override
    public String toString(){
        return id+" "+username+" "+pwd+" "+name+" "+gender;
    }
    public User(){
        super();
    }
    public User(int id,String username,String pwd,String name,String gender){
        super();
        this.id=id;
        this.username=username;
        this.pwd=pwd;
        this.name=name;
        this.gender=gender;
    }

    public int getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }
}

step3：创建三个dao类
数据库连接类dao.DBUtil类

package dao;

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

public class DBUtil {
   
   
    //新建一个连接
    public static Connection getConnection()throws Exception{
        Connection conn=null;
        try {
            //加载驱动
            Class.forName("com.mysql.jdbc.Driver");
            //创建实例
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "123456");
        } catch (Exception e) {
            e.printStackTrace();
            throw e;
        }

        return conn;
    }
    //关闭数据库连接
    public static void close(Connection conn)throws Exception{
        if(conn!=null){
            try {
                conn.close();
            } catch (Exception e) {
                e.printStackTrace();
                throw e;
            }
        }
    }
}

dao.EmployeeDAO类

package dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import javax.swing.text.html.HTMLDocument.HTMLReader.ParagraphAction;

import entity.Employee;

public class EmployeeDAO {
   
   
    //查询所有员工
    public List<Employee> findAll()throws Exception{
        List<Employee> emps=new ArrayList<Employee>();
        Connection conn=null;
        PreparedStatement stmt=null; // PreparedStatement 实例包含已编译的 SQL 语句
        ResultSet rs=null;
        try {
            conn=DBUtil.getConnection();
            stmt=conn.prepareStatement("select * from t_emp");
            rs=stmt.executeQuery();
            while(rs.next()){
                Employee emp=new Employee(
                        rs.getInt("id"),
                        rs.getString("name"),
                        rs.getFloat("salary"),
                        rs.ge