JDBC：从原生到进阶

版权声明：本文为博主转载文章。 https://blog.csdn.net/qq_35495339/article/details/89424545

原生的方式：自己写jdbc工具类

public class JDBCUtils {
    public static String URL; //数据库地址
    public static String USERNAME; //账户名
    public static String PASSWORD;  //密码
    static {  //静态代码块  加载JDBC驱动 并从配置文件中读取数据库url 用户名与密码
        try {
            Class.forName("com.mysql.jdbc.Driver");  //加载JDBC驱动
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        //从配置文件中中读取
        Properties properties =new Properties();
        BufferedReader bufferedReader=null;
        try {
            bufferedReader = new BufferedReader(new FileReader("D:\\IDEAProject\\firstWeb\\src\\com\\sunwenxu\\utils\\jdbc.properties"));//此处为你的配置文件绝对地址
            properties.load(bufferedReader);
            // 获取key对应的value值
            URL=properties.getProperty("jdbc.url");
            USERNAME=properties.getProperty("jdbc.userName");
            PASSWORD=properties.getProperty("jdbc.password");
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                bufferedReader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    //获取连接对象 供外部使用
    public static Connection getConnection(){
        Connection connection=null;
        try {
            connection= DriverManager.getConnection(URL, USERNAME, PASSWORD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }
    //重载的三个数据库连接关闭方法
    public static void close(Connection connection){
        close(connection,null);
    }
    public static void close(Connection connection, Statement statement){
        close(connection,statement,null);
    }
    public static void close(Connection connection, Statement statement, ResultSet rs){
        if (rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(statement !=null){
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(connection !=null){
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

配置文件（jdbc.properties）如下

jdbc.url=jdbc:mysql://localhost:3306/mydb01
jdbc.userName=root
jdbc.password=12345

使用以获取user为例

public User getUserById(String id) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        User user = null;
        try {
            connection = JDBCUtils.getConnection();  //从工具类中获取连接对象
            String sql = "select * from tb_user where userId = ?";  //编写sql语句
            preparedStatement = connection.prepareStatement(sql); 
            preparedStatement.setString(1, id);  //字符串拼接
            resultSet = preparedStatement.executeQuery();//执行查询语句
			/*PreparedStatement preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setDouble(1, money);
            preparedStatement.setInt(2, account.getAccountId());
            row = preparedStatement.executeUpdate();*/
            while (resultSet.next()) {
                user = new User();
                //rs .getXX方法中参数：（1）字段名，（2）序号（从1开始）
                String userId = resultSet.getString(1);
                String userName = resultSet.getString(2);
                String password = resultSet.getString(3);
                user.setUserId(userId);
                user.setUserName(userName);
                user.setPassword(password);
            }
        } catch(SQLException e)
        {
            e.printStackTrace();
        }finally {
            JDBCUtils.close(connection, preparedStatement, resultSet); //断开连接
        }
        return user; 
}

进阶1 （使用DbUtils工具类帮助我们简化dao层的操作）

配置文件和我们自己封装的jdbc工具类不用改
以修改上面获取user方法为例演示如何使用DbUtils来简化我们的操作

public User getUserByIdv2(String id) {
        Connection connection = null;
        User user = null;
        try {
            connection = JDBCUtils.getConnection();
            String sql = "select * from tb_user where userId = ?"；
            Object[] params={id}; //参数
            QueryRunner qr = new QueryRunner(); //改动 使用QueryRunner帮助我们执行sql语句并返回指定格式的对象
            user = qr.query(connection, sql, new BeanHandler<>(User.class),params);
        } catch(SQLException e)
        {
            e.printStackTrace();
        }finally {
            try {
                DbUtils.close(connection);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return user;
}

进阶2 使用c3p0帮助我们连接维护数据库连接节省资源

创建c3p0配置文件c3p0-config.xml（程序会自动去读取）

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
  <default-config>
    <property name="driverClass">com.mysql.jdbc.Driver</property>//驱动 不需要改动
	<property name="jdbcUrl">jdbc:mysql://localhost:3306/mydb01</property>   //自己需要连接的数据库
	<property name="user">root</property> //用户名
	<property name="password">123456</property>// 密码
	<property name="initialPoolSize">5</property>//初始化连接池数量
	<property name="maxPoolSize">20</property>//最大连接数量
  </default-config>
</c3p0-config>

以修改上面获取user方法为例演示如何使用c3p0和DbUtils来简化我们的操作

public User getUserByIdv3(String id) {
        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource(); 
        Connection connection = null;
        User user = null;
        try {
            connection = comboPooledDataSource.getConnection();
            String sql = "select * from tb_user where userId = ?";
            Object[] params={id};
            QueryRunner qr = new QueryRunner();
            user = qr.query(connection, sql, new BeanHandler<>(User.class),params);
        } catch(SQLException e)
        {
            e.printStackTrace();
        }
        return user;
}

如何在不适用框架的情况下添加jar包请查看如何在项目中添加jar包

持续更新中。。。