Interview question

How do you handle SQLException properly in JDBC applications? JDBC applications में SQLException को सही से कैसे handle करें?

Answer

SQLException is a checked exception carrying database-specific error information (SQL state, vendor error code, and a chain of related exceptions), and connections/statements/result sets must be properly closed even when errors occur.

public List<User> getUsers() {
    List<User> users = new ArrayList<>();
    String sql = 'SELECT id, name FROM users';

    try (Connection conn = dataSource.getConnection();
         PreparedStatement pstmt = conn.prepareStatement(sql);
         ResultSet rs = pstmt.executeQuery()) {

        while (rs.next()) {
            users.add(new User(rs.getInt('id'), rs.getString('name')));
        }

    } catch (SQLException e) {
        // SQLException carries extra diagnostic info beyond getMessage()
        System.out.println('SQL State: ' + e.getSQLState());
        System.out.println('Error Code: ' + e.getErrorCode());
        System.out.println('Message: ' + e.getMessage());

        // SQLException can be CHAINED - multiple related exceptions
        SQLException next = e.getNextException();
        while (next != null) {
            System.out.println('Chained: ' + next.getMessage());
            next = next.getNextException();
        }

        throw new RuntimeException('Failed to fetch users', e);  // wrap and rethrow with context
    }
    return users;
}

// try-with-resources handles closing automatically, even on exceptions -
// this avoids the old, verbose pattern of manually closing in finally blocks:
// finally {
//     if (rs != null) try { rs.close(); } catch (SQLException e) {}
//     if (pstmt != null) try { pstmt.close(); } catch (SQLException e) {}
//     if (conn != null) try { conn.close(); } catch (SQLException e) {}
// }

// Common SQLState prefixes: '08' = connection error, '23' = integrity
// constraint violation (e.g. duplicate key), '42' = syntax error

SQLException एक checked exception है जो database-specific error information रखती है (SQL state, vendor error code, related exceptions की chain), connections/statements/result sets को error होने पर भी सही से close करना ज़रूरी है।

public List<User> getUsers() {
    List<User> users = new ArrayList<>();
    String sql = 'SELECT id, name FROM users';

    try (Connection conn = dataSource.getConnection();
         PreparedStatement pstmt = conn.prepareStatement(sql);
         ResultSet rs = pstmt.executeQuery()) {

        while (rs.next()) {
            users.add(new User(rs.getInt('id'), rs.getString('name')));
        }

    } catch (SQLException e) {
        System.out.println('SQL State: ' + e.getSQLState());
        System.out.println('Error Code: ' + e.getErrorCode());
        System.out.println('Message: ' + e.getMessage());

        SQLException next = e.getNextException();
        while (next != null) {
            System.out.println('Chained: ' + next.getMessage());
            next = next.getNextException();
        }

        throw new RuntimeException('Users fetch नहीं हुए', e);
    }
    return users;
}

// try-with-resources automatically close करता है, exceptions पर भी

// Common SQLState prefixes: '08' = connection error, '23' = integrity
// violation, '42' = syntax error

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