如何在Android中获取当前的UTC在线时间？

Question

我正在使用UTC时区和我的应用程序中的时间来获取数据.在应用程序中,用户可以获取UTC时间并用于获取数据.我用这种方法来获取UTC时间.

String format = "yyyy-MM-dd HH:mm:ss";
final SimpleDateFormat sdf = new SimpleDateFormat(format);
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
String utcTime = sdf.format(new Date());

该应用程序运行正常.但它正在将系统时间转换为UTC时间.问题是有时用户可以将时间更改为错误的时间.所以数据还没有到来.

上述问题的案例是:

例如,印度的当前日期时间是2012年7月26日星期四,时间14:27:56,加尔各答时区.那么太平洋时区的时间应该是2012年7月26日星期四,太平洋时间01:59:30.

但是用户将设备时间从14:27:56更改为13:27:56,因此转换后的UTC时间将是2012年7月26日星期四,太平洋时间00:59:30.此时我的应用程序因为一小时的差异而无法获取日期.

我不想使用日期,Java的Calendar类,我不想使用设备时间.如何直接获取UTC时间,而不涉及设备的时间和日期.是否有任何开源API？

提前致谢.

Answer 1

long dateInMillis = System.currentTimeMillis();

这将返回自UTC 1970年1月1日00:00:00以来的毫秒数。

然后只需将其解析为所需的最合适的格式即可：

String format = "yyyy-MM-dd HH:mm:ss";
final SimpleDateFormat sdf = new SimpleDateFormat(format);

String dateString = sdf.format(new Date(dateInMillis)));

Answer 2

如果Sytem时间改变,例如手动8小时,则上面的SntpClient上的UTC时间不起作用.因为它使用System.currentTimeMillis返回false值!

        // get current time and write it to the request packet
        long requestTime = System.currentTimeMillis();
        long requestTicks = SystemClock.elapsedRealtime();

最好使用此类从NTP服务器获取正确的UTC时间:

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;


class NTP_UTC_Time
{
private static final String TAG = "SntpClient";

private static final int RECEIVE_TIME_OFFSET = 32;
private static final int TRANSMIT_TIME_OFFSET = 40;
private static final int NTP_PACKET_SIZE = 48;

private static final int NTP_PORT = 123;
private static final int NTP_MODE_CLIENT = 3;
private static final int NTP_VERSION = 3;

// Number of seconds between Jan 1, 1900 and Jan 1, 1970
// 70 years plus 17 leap days
private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;

private long mNtpTime;

public boolean requestTime(String host, int timeout) {
    try {
        DatagramSocket socket = new DatagramSocket();
        socket.setSoTimeout(timeout);
        InetAddress address = InetAddress.getByName(host);
        byte[] buffer = new byte[NTP_PACKET_SIZE];
        DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, NTP_PORT);

        buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);

        writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET);

        socket.send(request);

        // read the response
        DatagramPacket response = new DatagramPacket(buffer, buffer.length);
        socket.receive(response);          
        socket.close();

        mNtpTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);            
    } catch (Exception e) {
      //  if (Config.LOGD) Log.d(TAG, "request time failed: " + e);
        return false;
    }

    return true;
}


public long getNtpTime() {
    return mNtpTime;
}


/**
 * Reads an unsigned 32 bit big endian number from the given offset in the buffer.
 */
private long read32(byte[] buffer, int offset) {
    byte b0 = buffer[offset];
    byte b1 = buffer[offset+1];
    byte b2 = buffer[offset+2];
    byte b3 = buffer[offset+3];

    // convert signed bytes to unsigned values
    int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
    int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
    int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
    int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);

    return ((long)i0 << 24) + ((long)i1 << 16) + ((long)i2 << 8) + (long)i3;
}

/**
 * Reads the NTP time stamp at the given offset in the buffer and returns 
 * it as a system time (milliseconds since January 1, 1970).
 */    
private long readTimeStamp(byte[] buffer, int offset) {
    long seconds = read32(buffer, offset);
    long fraction = read32(buffer, offset + 4);
    return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L);        
}

/**
 * Writes 0 as NTP starttime stamp in the buffer. --> Then NTP returns Time OFFSET since 1900
 */    
private void writeTimeStamp(byte[] buffer, int offset) {        
    int ofs =  offset++;

    for (int i=ofs;i<(ofs+8);i++)
      buffer[i] = (byte)(0);             
}

}

并使用它:

        long now = 0;

        NTP_UTC_Time client = new NTP_UTC_Time();

        if (client.requestTime("pool.ntp.org", 2000)) {              
          now = client.getNtpTime();
        }

如果你需要UTC时间"现在"作为DateTimeString使用函数:

private String get_UTC_Datetime_from_timestamp(long timeStamp){

    try{

        Calendar cal = Calendar.getInstance();
        TimeZone tz = cal.getTimeZone();

        int tzt = tz.getOffset(System.currentTimeMillis());

        timeStamp -= tzt;

        // DateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss",Locale.getDefault());
        DateFormat sdf = new SimpleDateFormat();
        Date netDate = (new Date(timeStamp));
        return sdf.format(netDate);
    }
    catch(Exception ex){
        return "";
     }
    } 

并使用它:

String UTC_DateTime = get_UTC_Datetime_from_timestamp(now);