如何用Java把数据库表和类关联起来？

一、表与类的关系

在Java中，我们可以把数据库表和类关联起来，这样就能更方便地操作数据库了。

1. 创建表并插入数据

CREATE TABLE IF NOT EXISTS employee(
    id int(11) auto_increment PRIMARY key,
    name VARCHAR(22),
    age int(4),
    money int(20)
);

INSERT into employee VALUES(null,"张三",20,3650);
INSERT into employee VALUES(null,"李四",30,4502);
INSERT into employee VALUES(null,"王五",30,3650);
INSERT into employee VALUES(null,"麻子",50,8885);
INSERT into employee VALUES(null,"小红",20,4445);

2. 查询表中数据

接下来，我们可以通过SQL语句查询表中的数据。

二、案例演示

1. 创建一个Employee类

public class Employee {
    private int id;
    private String name;
    private int age;
    private int money;

    public Employee() {
    }

    public Employee(int id, String name, int age, int money) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.money = money;
    }

    // 省略其他getter和setter方法...

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", money=" + money +
                '}';
    }
}

2. PreparedStatement

使用PreparedStatement查询数据，并封装成对象，存入一个集合中。

public class demo1 {
    public static void main(String[] args) throws ClassNotFoundException {
        ResourceBundle rb = ResourceBundle.getBundle("config/jdbc");
        Class.forName(rb.getString("Driver"));
        Connection con = null;
        PreparedStatement pre = null;
        ResultSet rs = null;
        List list = new ArrayList<>();
        try {
            con = DriverManager.getConnection(rb.getString("url"), rb.getString("user"), rb.getString("password"));
            String sql = "select * from employee";
            pre = con.prepareStatement(sql);
            rs = pre.executeQuery(sql);
            Employee emp = null;
            while (rs.next()) {
                emp = new Employee();
                emp.setId(rs.getInt("id"));
                emp.setName(rs.getString("name"));
                emp.setAge(rs.getInt("age"));
                emp.setMoney(rs.getInt("money"));
                list.add(emp);
            }
            System.out.println(list);
            System.out.println("操作完成!");
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            try {
                pre.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
            if (con != null) {
                try {
                    con.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
        }
    }
}

三、小结与拓展

通过上面的案例，我们学会了如何将数据库表和Java类关联起来，并通过PreparedStatement查询数据。这是一个非常实用的技能，希望对大家有所帮助。

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