To fetch results using a ResultSet in Java JDBC, you follow a standard pattern of executing a query, iterating through the rows, and extracting data using “getter” methods.

Basic Fetching Pattern

1. Execute the Query: Use stmt.executeQuery(sql) (for Statement) or pstmt.executeQuery() (for PreparedStatement).
2. Iterate through Rows: Use a while (rs.next()) loop. The next() method moves the cursor to the next row and returns false when there are no more rows.
3. Retrieve Values: Use methods like getString(), getInt(), getLong(), or getBigDecimal() based on the column type.

Example

try (Connection conn = DriverManager.getConnection(url, user, pass);
     Statement stmt = conn.createStatement();
     ResultSet rs = stmt.executeQuery("SELECT id, name, created_at FROM users")) {

    while (rs.next()) {
        // 1. Fetch by Column Name (Recommended for readability)
        int id = rs.getInt("id");
        String name = rs.getString("name");

        // 2. Fetch by Column Index (1-based, often faster)
        java.sql.Timestamp date = rs.getTimestamp(3);

        System.out.println("User: " + id + " | Name: " + name);
    }
} catch (SQLException e) {
    e.printStackTrace();
}

Key Considerations

• 1-Based Indexing: If you use column indices (e.g., rs.getString(1)), remember that JDBC indices start at 1, not 0.
• Column Names vs. Indices:
  • Names: More maintainable and easier to read.
  • Indices: Slightly better performance as the driver doesn’t have to look up the column mapping.
• Try-with-Resources: Always wrap the ResultSet in a try-with-resources block (or ensure it is closed in a finally block) to prevent database cursor leaks.
• Data Types: Use the getter that matches your database schema:
  • rs.getInt() for INTEGER
  • rs.getString() for VARCHAR/TEXT
  • rs.getBigDecimal() for DECIMAL/NUMERIC (best for currency)
  • rs.getBoolean() for BIT/BOOLEAN
• Handling Nulls: If a column allows NULL, primitive getters (like getInt) will return 0. To check if the value was actually null in the database, call rs.wasNull() immediately after the getter.