前言

　　寫這個部落格是因為這段時間寫NoHttp時遇到格式話Http響應頭和請求頭中和Data有關的欄位時遇到的一些問題，最後總結了一下演算法。
　　2個概念明確下：
　　1. 格林尼治時間（有的出版局叫格林威治Greenwhich）的格式：”EEE, dd MMM y HH:mm:ss ‘GMT’”
　　2. 毫秒格式：1464709616971

格林尼治（EEE, dd MMM y HH:mm:ss ‘GMT’）轉化為毫秒

public static final String FORMAT_HTTP_DATA = "EEE, dd MMM y HH:mm:ss 'GMT'"
 
;

public static final TimeZone GMT_TIME_ZONE = TimeZone.getTimeZone("GMT");

/**
 * Parsing the TimeZone of time in milliseconds.
 *
 * @param gmtTime GRM Time, Format such as: {@value #FORMAT_HTTP_DATA}.
 * @return The number of milliseconds from 1970.1.1.
 * @throws ParseException if an error occurs during parsing.
 */
 

public static long parseGMTToMillis(String gmtTime) throws ParseException {
    SimpleDateFormat formatter = new SimpleDateFormat(FORMAT_HTTP_DATA, Locale.US);
    formatter.setTimeZone(GMT_TIME_ZONE);
    Date date = formatter.parse(gmtTime);
    return date.getTime();
}

毫秒轉化為格林尼治（EEE, dd MMM y HH:mm:ss ‘GMT’）

public static final String FORMAT_HTTP_DATA = "EEE, dd MMM y HH:mm:ss 'GMT'";

public static final TimeZone GMT_TIME_ZONE = TimeZone.getTimeZone("GMT");

/**
 * Parsing the TimeZone of time from milliseconds.
 *
 * @param milliseconds the number of milliseconds from 1970.1.1.
 * @return GRM Time, Format such as: {@value #FORMAT_HTTP_DATA}.
 */
public static String formatMillisToGMT(long milliseconds) {
    Date date = new Date(milliseconds);
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat(FORMAT_HTTP_DATA, Locale.US);
    simpleDateFormat.setTimeZone(GMT_TIME_ZONE);
    return simpleDateFormat.format(date);
}

合起來寫成一個類HttpDate

public final class HttpDateTime {

    public static final String FORMAT_HTTP_DATA = "EEE, dd MMM y HH:mm:ss 'GMT'";

    public static final TimeZone GMT_TIME_ZONE = TimeZone.getTimeZone("GMT");

    /**
     * Parsing the TimeZone of time in milliseconds.
     *
     * @param gmtTime GRM Time, Format such as: {@value #FORMAT_HTTP_DATA}.
     * @return The number of milliseconds from 1970.1.1.
     * @throws ParseException if an error occurs during parsing.
     */
    public static long parseGMTToMillis(String gmtTime) throws ParseException {
        SimpleDateFormat formatter = new SimpleDateFormat(FORMAT_HTTP_DATA, Locale.US);
        formatter.setTimeZone(GMT_TIME_ZONE);
        Date date = formatter.parse(gmtTime);
        return date.getTime();
    }

    /**
     * Parsing the TimeZone of time from milliseconds.
     *
     * @param milliseconds the number of milliseconds from 1970.1.1.
     * @return GRM Time, Format such as: {@value #FORMAT_HTTP_DATA}.
     */
    public static String formatMillisToGMT(long milliseconds) {
        Date date = new Date(milliseconds);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(FORMAT_HTTP_DATA, Locale.US);
        simpleDateFormat.setTimeZone(GMT_TIME_ZONE);
        return simpleDateFormat.format(date);
    }

    /**
     * Returned the local number of milliseconds after 100.
     *
     * @return Long format time.
     */
    public static long getMaxExpiryMillis() {
        return System.currentTimeMillis() + 1000L * 60L * 60L * 24L * 365L * 100L;
    }

}

　　最後一個方法是得到一個100年的毫秒時間，有的同學算到的是錯的，問題出在有的數字後面沒有L，所以超出了int的極限，所以得到值比預想的要小。