浅析Java如何防范SQL注入攻击

String username = request.getParameter("username");
String password = request.getParameter("password");

String query = "SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "'";
try (Statement stmt = connection.createStatement()) {
    ResultSet rs = stmt.executeQuery(query);
    if (rs.next()) {
        // 用户认证成功
    } else {
        // 用户认证失败
    }
} catch (SQLException e) {
    e.printStackTrace();
}

SELECT * FROM users WHERE username='' OR 1=1 -- AND password=''

String searchKey = request.getParameter("searchKey");
String query = "SELECT * FROM products WHERE name LIKE '%" + searchKey + "%'";
try (Statement stmt = connection.createStatement()) {
    ResultSet rs = stmt.executeQuery(query);
    // 处理结果
} catch (SQLException e) {
    e.printStackTrace();
}

SELECT * FROM products WHERE name LIKE '%'; DELETE FROM products; --'

String username = request.getParameter("username");
String password = request.getParameter("password");

String query = "SELECT * FROM users WHERE username=? AND password=?";
try (PreparedStatement pstmt = connection.prepareStatement(query)) {
    pstmt.setString(1, username);
    pstmt.setString(2, password);
    ResultSet rs = pstmt.executeQuery();
    if (rs.next()) {
        // 用户认证成功
    } else {
        // 用户认证失败
    }
} catch (SQLException e) {
    e.printStackTrace();
}

String username = request.getParameter("username");
String password = request.getParameter("password");

// 验证用户名和密码是否为空
if (username == null || username.trim().isEmpty()) {
    throw new IllegalArgumentException("用户名不能为空");
}

if (password == null || password.trim().isEmpty()) {
    throw new IllegalArgumentException("密码不能为空");
}

// 验证用户名和密码的长度
if (username.length() > 50 || password.length() > 50) {
    throw new IllegalArgumentException("用户名或密码过长");
}

// 使用正则表达式验证用户名和密码是否只包含字母和数字
if (!username.matches("^[a-zA-Z0-9]+$") || !password.matches("^[a-zA-Z0-9]+$")) {
    throw new IllegalArgumentException("用户名和密码只能包含字母和数字");
}