Java之JDBC詳解

JDBC

JDBC(Java Database connectivity)是一種執行SQL語句的Java API
可以爲多種關係數據庫提供統一訪問
Java數據庫連接規範(即一套接口)
JDBC四個核心類:
    DriverManager 創建連接
    Connection    連接類
    Statement     用來執行sql語句
    ResultSet     結果集
JDBC連接步驟:
    1.註冊驅動
    2.獲取連接 Connection
    3.獲取sql語句的執行對象 Statement
    4.執行sql語句 返回結果集 ResultSet
    5.處理結果集
    6.關閉資源

JDBC的連接

    // 1.註冊驅動
    /*  這種註冊方式 相當於註冊了兩遍
        Driver類內部的靜態代碼塊已經註冊了一遍
        DriverManager.registerDriver(new Driver());
    */
    // 直接把該類加載到內存當中 參數是全限定類名 (包名+類名)
    Class.forName("com.mysql.jdbc.Driver");

    // 2.獲取連接對象
    // url是訪問數據庫連接地址
    String url = "jdbc:mysql://localhost:3306/myjdbc";

    // 獲取連接的方式一
    Connection connection = DriverManager.getConnection(url, "root", "123456");

    // 獲取連接的方式二
    Properties info = new Properties();
    // 添加用戶名 密碼
    info.setProperty("user", "root");
    info.setProperty("password", "123456");
    Connection connection = DriverManager.getConnection(url, info);

    // 獲取連接的方式三 相當於使用了一個get請求
    // 攜帶參數 訪問連接
    String url2 = "jdbc:mysql://localhost:3306/myjdbc?user=root&password=123456";
    Connection connection = DriverManager.getConnection(url2);

    // 3.獲取執行sql語句的對象 Statement
    Statement statement = connection.createStatement();

    // 4.執行sql語句 返回結果集
    String sql = "select * from users";
    ResultSet resultSet = statement.executeQuery(sql);

    // 5.處理結果集
    // 循環遍歷結果集輸出結果
    // 有記錄next()方法返回true 反之false
    while (resultSet.next()) {
        // 打印數據
        // 注意:查詢數據庫時 索引從1開始
        // 結果集中添加的索引要和查詢語句中的字段對應
        System.out.println(resultSet.getObject(1));
        System.out.println(resultSet.getObject(2));
        System.out.println(resultSet.getObject(3));
        System.out.println(resultSet.getObject(4));
        System.out.println(resultSet.getObject(5));
    }

    // 6.關閉資源
    resultSet.close();
    statement.close();
    connection.close();

JDBC增刪改查

@Test註解用來測試方法
注意:要使用public修飾的、無返回值的方法

    // 插入方法
    @Test
    public void testInsert() throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/myjdbc";
        Connection connection = DriverManager.getConnection(url, "root", "123456");
        Statement statement = connection.createStatement();
        String sql = "insert into users values(5,'ab','123','[email protected]','1997-06-23')";
        // executeUpdate 增刪改
        // row 表示受影響的行數
        int row = statement.executeUpdate(sql);
        if (row>0) {
            System.out.println("成功插入"+ row +"行");
        }
        connection.close();
        statement.close();
    }

    // 更新方法
    @Test
    public void testUpdate() throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/myjdbc";
        Connection connection = DriverManager.getConnection(url, "root", "123456");
        Statement statement = connection.createStatement();
        String sql = "update users set name='ac' where name='ab'";
        int row = statement.executeUpdate(sql);
        if (row>0) {
            System.out.println("成功更新"+ row +"行");
        }
        connection.close();
        statement.close();
    }

    // 刪除方法
    @Test
    public void testDelete() throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/myjdbc";
        Connection connection = DriverManager.getConnection(url, "root", "123456");
        Statement statement = connection.createStatement();
        String sql = "delete from users where id=5";
        // 增刪改
        int row = statement.executeUpdate(sql);
        if (row >0) {
            System.out.println("成功刪除"+ row +"行");
        }
        connection.close();
        statement.close();
    }

    // 查詢方法
    @Test
    public void testSelect() throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/myjdbc";
        Connection connection = DriverManager.getConnection(url, "root", "123456");
        Statement statement = connection.createStatement();
        // 查詢
        String sql = "select id,name,email from users";
        ResultSet resultSet = statement.executeQuery(sql);
        // 處理結果集
        while (resultSet.next()) {
            // 可以直接填字段名稱
            System.out.println(resultSet.getObject("id"));
            System.out.println(resultSet.getObject("name"));
            System.out.println(resultSet.getObject("email"));
        }
        resultSet.close();
        connection.close();
        statement.close();
    }

JDBC連接數據庫的異常處理

    Connection connection = null;
    Statement statement = null;
    ResultSet resultSet = null;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/myjdbc", "root", "123456");
        statement = connection.createStatement();
        String sql = "select * from users";
        resultSet = statement.executeQuery(sql);

        // 處理結果集(把數據庫的記錄封裝到對象中)
        // 把對象保存到集合當中
        ArrayList<User> list = new ArrayList<>();
        while (resultSet.next()) {
            // 創建user對象
            User user = new User();
            user.setId(resultSet.getInt("id"));
            user.setName(resultSet.getString("name"));
            user.setPassword(resultSet.getString("password"));
            user.setEmail(resultSet.getString("email"));
            user.setBirthday(resultSet.getDate("birthday"));
            // 放入集合中
            list.add(user);
        }
        // 遍歷打印
        for (User user : list) {
            System.out.println(user);
        }
    } catch (ClassNotFoundException e) {
        // 停止程序
        throw new RuntimeException("驅動加載失敗");
    } catch (SQLException e) {
        throw new RuntimeException("獲取連接失敗");
    } finally {
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            // 加快系統回收的速度
            resultSet = null;
        }
        if (statement != null) {
            try {
                statement.close();
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            statement = null;
        }
        if (connection != null) {
            try {
                connection.close(); 
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            connection = null;
        }       
    }

JDBC工具類

JDBCUtil工具類

public class JDBCUtil {
    private static String driverClass;
    private static String url;
    private static String user;
    private static String password;

    // 使用靜態代碼塊加載驅動、讀取配置文件（讓驅動類只加載一次）
    static {
        // 使用系統類來讀取配置文件
        ResourceBundle rb = ResourceBundle.getBundle("dbinfo");
        // 獲取文件中的數據
        driverClass = rb.getString("driverClass");
        url = rb.getString("url");
        user = rb.getString("user");
        password = rb.getString("password");
        try {
            Class.forName(driverClass);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        /*
        // 利用集合 讀取文件
        Properties properties = new Properties();
        try {
            FileInputStream fis = new FileInputStream("src/dbinfo.properties");
            properties.load(fis);
            // 讀取文件
            driverClass = properties.getProperty("driverClass");
            url = properties.getProperty("url");
            user = properties.getProperty("user");
            password = properties.getProperty("password");
        } catch (Exception e) {
        }
        */
    }

    // 獲取數據庫連接的方法
    public static Connection getConnection() throws ClassNotFoundException, SQLException {
        return DriverManager.getConnection(url, user, password);
    }
    // 關閉數據庫的方法 如果沒有結果集需要關閉 直接傳null
    public static void closeAll(ResultSet resultSet, Statement statement, Connection connection) {
        // 關閉資源前進行非空判斷防止空指針出現
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            // 加快系統回收的速度
            resultSet = null;
        }
        if (statement != null) {
            try {
                statement.close();
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            statement = null;
        }
        if (connection != null) {
            try {
                connection.close(); 
            } catch (SQLException e) {
                throw new RuntimeException("關閉失敗");
            }
            connection = null;
        }   
    }
}

TestJDBCUtil測試類

public class TestJDBCUtil {
    Connection connection = null;
    Statement statement = null;
    ResultSet resultSet = null;
    @Test
    public void testSelect() {
        try {
            // 獲取連接
            connection = JDBCUtil.getConnection();
            statement = connection.createStatement();
            String sql = "select * from users";
            resultSet = statement.executeQuery(sql);
            ArrayList<User> list = new ArrayList<>();
            while (resultSet.next()) {
                User user = new User();
                user.setId(resultSet.getInt("id"));
                user.setName(resultSet.getString("name"));
                user.setPassword(resultSet.getString("password"));
                user.setEmail(resultSet.getString("email"));
                user.setBirthday(resultSet.getDate("birthday"));
                list.add(user);
            }
            for (User user : list) {
                System.out.println(user);
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            // 關閉資源
            JDBCUtil.closeAll(resultSet, statement, connection);
        }
    }
}

JDBC實現用戶登錄

用戶登錄

public class Login {
    public static void main(String[] args) {
        // 接收用戶輸入的賬號和密碼
        System.out.println("請輸入賬號:");
        Scanner scanner = new Scanner(System.in);
        String name = scanner.nextLine();
        System.out.println("請輸入密碼:");
        String password = scanner.nextLine();
        // 調用查詢方法
        DoLogin dl = new DoLogin();
        User user = dl.findUser(name, password);
        if (user != null) {
            System.out.println(user.getName()+"登錄成功");
        } else {
            System.out.println("登錄失敗");
        }
    }
}

處理登錄的查詢操作

public class DoLogin {
    public User findUser(String name,String password) {
        User user = null;
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        String sql = "select * from users where name='"+name+"' and password='"+password+"'";
        // 查詢數據庫
        try {
            connection = JDBCUtil.getConnection();
            statement = connection.createStatement();
            resultSet = statement.executeQuery(sql);
            if (resultSet.next()) {
                user = new User();
                user.setId(resultSet.getInt("id"));
                user.setName(resultSet.getString("name"));
                user.setPassword(resultSet.getString("password"));
                user.setEmail(resultSet.getString("email"));
                user.setBirthday(resultSet.getDate("birthday"));
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtil.closeAll(resultSet, statement, connection);
        }
        return user;
    }
}

sql語句注入問題(添加了一個恆成立的條件)
解決方法

public class DoLogin {
    public User findUser(String name,String password) {
        User user = null;
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        // 佔位符
        String sql = "select * from users where name=? and password=?";
        // 查詢數據庫
        try {
            connection = JDBCUtil.getConnection();
            // 對sql語句進行預編譯
            statement = connection.prepareStatement(sql);
            // 給sql語句的佔位符 進行賦值
            // 參數1 填索引 sql語句中問號索引
            statement.setString(1, name);
            statement.setString(2, password);
            resultSet = statement.executeQuery();
            if (resultSet.next()) {
                user = new User();
                user.setId(resultSet.getInt("id"));
                user.setName(resultSet.getString("name"));
                user.setPassword(resultSet.getString("password"));
                user.setEmail(resultSet.getString("email"));
                user.setBirthday(resultSet.getDate("birthday"));
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtil.closeAll(resultSet, statement, connection);
        }
        return user;
    }