MySQL——statement对象详解

JDBC中的statement对象用于向数据库发送SQL语句，想完成对数据库的增删改查，只需要通过这个对象向数据库发送增删改查语句即可。

Statement对象的executeUpdate方法，用于向数据库发送增、删、改的sql语句，executeUpdate执行完成后，将会返回一个整数（即增删改语句导致了数据库几行数据发生了变化）。

Statement.executeQuery方法用于向数据库发送查询语句，executeQuery方法返回代表查询结果的ResultSet对象。

CRUD操作-create

使用executeUpdate(String sql)方法完成数据添加操作，示例操作：

Statement st = conn.createStatement();
String sql = "insert into user(... .) values(... . .)"
int num = st.executeUpdate(sql);
if(num > 0){
    System.out.println("插入成功！");
}

CRUD操作-delete

使用executeUpdate(String sql)方法完成数据删除操作，示例操作：

Statement st = conn.createStatement();
String sql = "delete from user where id=1"
int num = st.executeUpdate(sql);
if(num > 0){
    System.out.println("删除成功！");
}

CRUD操作-update

使用executeUpdate(String sql)方法完成数据修改操作，示例操作：

Statement st = conn.createStatement();
String sql = "update user set name='' where name=''"
int num = st.executeUpdate(sql);
if(num > 0){
    System.out.println("修改成功！");
}

CRUD操作-read

使用executeQuery(String sql)方法完成数据查询操作，示例操作：

Statement st = conn.createStatement();
String sql = "select * from user where id=1"
ResultSet rs = st.executeQuery(sql);
while(rs.next()){
    // 根据获取列的数据类型，分别调用rs的相应方法映射到java对象中
}

---

代码实现

1. 提取工具类

public class jdbcUtils {

    private static String driver = null;
    private static String url = null;
    private static String username = null;
    private static String password = null;

    static {

        try {
            InputStream in = jdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");// 获取具体资源
            Properties properties = new Properties();
            properties.load(in);

            driver = properties.getProperty("driver");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");

            // 1.驱动只用加载一次
            Class.forName(driver);

        } catch (IOException | ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

    // 获取连接
    public  static Connection  getConnection() throws SQLException {
        return DriverManager.getConnection(url,username,password);
    }

    // 释放连接资源
    public static void release(Connection conn, Statement stmt, ResultSet rs) throws SQLException {
        if (rs!=null){
            rs.close();
        }
        if (stmt!=null){
            stmt.close();
        }
        if (conn!=null){
            conn.close();
        }
    }

}

2. 编写增删改的方法，executeUpdate

增：

public class TestInsert {
    public static void main(String[] args) throws SQLException {

        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;

        try {
            conn = jdbcUtils.getConnection();  // 获取数据库连接
            st = conn.createStatement();  // 获得SQL的执行对象
            String sql = "INSERT INTO users(id,`NAME`,`PASSWORD`,`email`,`birthday`)" +
                    "VALUES(4,'chenyang','123456','888@qq.com','2024-7-5')";

            int i = st.executeUpdate(sql);
            if (i>0){
                System.out.println("插入成功！");
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            jdbcUtils.release(conn,st,rs);
        }
    }
}

删：

public class TestDelete {
    public static void main(String[] args) throws SQLException {

        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;

        try {
            conn = jdbcUtils.getConnection();
            st = conn.createStatement();
            String sql = "DELETE FROM users WHERE id=4";

            int i = st.executeUpdate(sql);

            if (i>0){
                System.out.println("删除成功！");
            }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            jdbcUtils.release(conn,st,rs);
        }
    }

改：

public class TestUpdate {
    public static void main(String[] args) throws SQLException {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;

        try {
            conn = jdbcUtils.getConnection();
            st = conn.createStatement();
            String sql = "UPDATE users SET `NAME`='chenyang8' WHERE id=4";

            int i = st.executeUpdate(sql);

            if (i>0){
                System.out.println("修改成功！");
            }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            jdbcUtils.release(conn,st,rs);
        }
    }
}

3. 查询，executeQuery

public class TestSelect {
    public static void main(String[] args) throws SQLException {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;

        try {
            conn = jdbcUtils.getConnection();
            st = conn.createStatement();
            //SQl
            String sql = "select * from users where id = 1";
            rs = st.executeQuery(sql);  //查询完毕会返回一个结果集

            if (rs.next()){
                System.out.println(rs.getString("NAME"));
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            jdbcUtils.release(conn,st,rs);
        }

    }
}