Apexでhttp-date (RFC1123)

DateFormat.cls

public class DateFormat {

    private static final Map<String, Integer> MONTHS = new Map<String, Integer> {
        'Jan' => 1, 'Feb' => 2, 'Mar' => 3, 'Apr' => 4, 'May' => 5, 'Jun' => 6,
        'Jul' => 7, 'Aug' => 8, 'Sep' => 9, 'Oct' => 10, 'Nov' => 11, 'Dec' => 12
    };

    public static Datetime fromRFC1123(String x) {
        String[] dateParts = x.split('[\\s:]');
        Integer year = Integer.valueOf(dateParts[3]);
        Integer month = MONTHS.get(dateParts[2]);
        Integer day = Integer.valueOf(dateParts[1]);
        Integer hour = Integer.valueOf(dateParts[4]);
        Integer minute = Integer.valueOf(dateParts[5]);
        Integer second = Integer.valueOf(dateParts[6]);
        return Datetime.newInstanceGmt(year, month, day, hour, minute, second);
    }

    public static String toRFC1123(Datetime x) {
        return x.formatGmt('EEE, dd MMM yyyy HH:mm:ss z');
    }

}