JDBC 小结

JDBC 小结

步骤总结

1. 加载驱动
2. 连接数据库 DriverManager
3. 获得执行sql的对象 Statement
4. 获得返回的结果集
5. 释放连接

        // 1.加载驱动
        Class.forName("com.mysql.jdbc.Driver");

        // 2.加载用户信息
        String url      = "jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf8&useSSL=false";
        String username = "root";
        String password = "132654";

        // 3.连接成功，数据库对象     connection代表数据库
        Connection connection = DriverManager.getConnection(url, username, password);

        // 4.执行sql对象            statement执行sql的对象
        Statement statement = connection.createStatement();

        // 5.执行sql的对象 去执行sql
        String sql = "select * from users";

        ResultSet resultSet = statement.executeQuery(sql);  // 返回的结果集

        while (resultSet.next()) {
            System.out.println("id=" + resultSet.getObject("id"));
            System.out.println("name=" + resultSet.getObject("name"));
            System.out.println("pwd=" + resultSet.getObject("password"));
            System.out.println("email=" + resultSet.getObject("email"));
            System.out.println("birthday=" + resultSet.getObject("birthday"));
            System.out.println("===============================");
        }

        // 释放连接
        resultSet.close();
        statement.close();
        connection.close();

RsultSet 查询的结果集：封装了所有的查询结果

获取指定的数据类型

resultSet.getObject();
resultSet.getString();
resultSet.getInt();
resultSet.getDouble();
resultSet.getDate();
resultSet.getBigDecimal();
resultSet.getTime();

遍历、指针

resultSet.next();
resultSet.beforeFirst();
resultSet.afterLast();
resultSet.previous();
resultSet.absolute(row);

释放资源 必不可少

释放连接

resultSet.close();
statement.close();
connection.close();

配置文件

配置文件（db.properties）

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf8&useSSL=false
username=root
password=132654

工具类（JdbcUtils）

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");
            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 (Exception e) {
            e.printStackTrace();
        }
    }


    // 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 connection, Statement statement, ResultSet resultSet) throws SQLException {
        if (resultSet != null) {
            resultSet.close();
        }
        if (statement != null) {
            statement.close();
        }
        if (connection != null) {
            connection.close();
        }
    }
}