I have an android device acting as server which connects to multiple bluetooth android clients.
I understand the concept of UUID and how it is unique.
My question is, can I use the same UUID for all my clients connecting to my server?
If not, how do I generate a UUID for my clients programmatically and let my server know about their UUIDs.
The problem started appearing after Android 8.1 where you no longer had access to bluetooth MAC address which I initially used to generate UUIDs for client android devices.
You can generate one like this.
First, is needed to generate as long the 64 least and most significant bits:
private static long get64LeastSignificantBitsForVersion1() {
Random random = new Random();
long random63BitLong = random.nextLong() & 0x3FFFFFFFFFFFFFFFL;
long variant3BitFlag = 0x8000000000000000L;
return random63BitLong + variant3BitFlag;
}
private static long get64MostSignificantBitsForVersion1() {
LocalDateTime start = LocalDateTime.of(1582, 10, 15, 0, 0, 0);
Duration duration = Duration.between(start, LocalDateTime.now());
long seconds = duration.getSeconds();
long nanos = duration.getNano();
long timeForUuidIn100Nanos = seconds * 10000000 + nanos * 100;
long least12SignificatBitOfTime = (timeForUuidIn100Nanos & 0x000000000000FFFFL) >> 4;
long version = 1 << 12;
return
(timeForUuidIn100Nanos & 0xFFFFFFFFFFFF0000L) + version + least12SignificatBitOfTime;
}
next you can use the above methods to build one UUID:
public static UUID generateType1UUID() {
long most64SigBits = get64MostSignificantBitsForVersion1();
long least64SigBits = get64LeastSignificantBitsForVersion1();
return new UUID(most64SigBits, least64SigBits);
}
Answer:
I finally found out that you can use a custom UUID using a generator and it works with multiple devices.
The UUID must be unique and should not collide with the ones that are common & public.
Hopefully someone finds it useful
Related
eg. I have a 1.5 GB data pack. It gives the total sum of 2.0 GB or more than that .
any idea about how to get correct speed every second.
TrafficStats.getTotalRxBytes() does not return your data pack value. It refers to the total received bytes (either wifi/mobile) since the last boot (turning ON phone). For mobile data, it will be TrafficStats.getMobileRxBytes(). More importantly, these values get reset in every reboot of device.
I have a 1.5 GB data pack. It gives the total sum of 2.0 GB or more
than that .
The android system does not know anything about your data pack. You are adding it again and again. When you call TrafficStats.getMobileRxBytes() at a moment, it returns total mobile data received upto this moment since last boot. Following is an explanation. Hope this helps.
// Suppose, you have just rebooted your device, then received 400 bytes and transmitted 300 bytes of mobile data
// After reboot, so far 'totalReceiveCount' bytes have been received by your device over mobile data.
// After reboot, so far 'totalTransmitCount' bytes have been sent from your device over mobile data.
// Hence after reboot, so far 'totalDataUsed' bytes used actually.
long totalReceiveCount = TrafficStats.getMobileRxBytes();
long totalTransmitCount = TrafficStats.getMobileTxBytes();
long totalDataUsed = totalReceiveCount + totalTransmitCount;
Log.d("Data Used", "" + totalDataUsed + " bytes"); // This will log 700 bytes
// After sometime passed, another 200 bytes have been transmitted from your device over mobile data.
totalDataUsed = TrafficStats.getMobileRxBytes() + TrafficStats.getMobileTxBytes();
Log.d("Data Used", "" + totalDataUsed + " bytes"); // Now this will log 900 bytes
any idea about how to get correct speed every second.
You cannot get actual speed this way. You can only calculate and show how much bytes have been received/transmitted in a second. All the speed meters in android do the same I think. Something like the following:
class SpeedMeter {
private long uptoNow = 0;
private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
private ScheduledFuture futureHandle;
public void startMeter() {
final Runnable meter = new Runnable() {
public void run() {
long now = TrafficStats.getMobileRxBytes() + TrafficStats.getMobileTxBytes();
System.out.println("Speed=" + (now - uptoNow)); // Prints value for current second
uptoNow = now;
}
};
uptoNow = TrafficStats.getMobileRxBytes() + TrafficStats.getMobileTxBytes();
futureHandle = scheduler.scheduleAtFixedRate(meter, 1, 1, SECONDS);
}
public void stopMeter() {
futureHandle.cancel(true);
}
}
And use like this:
SpeedMeter meter = new SpeedMeter();
meter.startMeter();
Although this code is not perfect, however it will suit your needs.
I want to genrate 5 digit extremly secure random numbers for some products verifications which should be always unique, their no limits how many times in day or how many times in a week i've to put this request for new generation of manual codes, and it can be in range of 1k - 20k, The main requirement is about to manual codes should have to be always UNIQUE(NON REPEATED) otherwise their would be a big clash.
so please assit me a better and secured way to genrated 5 digit unique codes,
Any recommendations would be very helpful.
for now i am using this reffrence :
private static final Random random = new Random();
private static final String CHARS = "abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWXYZ234567890!##$";
public static String getToken(int length) {
StringBuilder token = new StringBuilder(length);
for (int i = 0; i < length; i++) {
token.append(CHARS.charAt(random.nextInt(CHARS.length())));
}
return token.toString();
}
After logging in, it's generating a hash value, but still giving error "Some problem occurred! try again".
PayUmoneySdkInitilizer.PaymentParam.Builder builder =
new PayUmoneySdkInitilizer.PaymentParam.Builder();
builder.setAmount(10.0)
.setTnxId("0nf7" + System.currentTimeMillis())
.setPhone(<My phone>)
.setProductName("product_name")
.setFirstName(<My Name>)
.setEmail(<My email>)
.setsUrl("https://www.payumoney.com/mobileapp/payumoney/success.php")
.setfUrl("https://www.payumoney.com/mobileapp/payumoney/failure.php")
.setUdf1("").setUdf2("").setUdf3("").setUdf4("").setUdf5("")
.setIsDebug(false)
.setKey(<mykey>)
.setMerchantId(<my debug merchant id>);
String tnxId="0nf7" + System.currentTimeMillis();
PayUmoneySdkInitilizer.PaymentParam paymentParam = builder.build();
String hashSequence = "<...>|"+tnxId+"|10.0|product_name|<My name>|<My email>|||||||||||salt";
String serverCalculatedHash= hashCal("SHA-512", hashSequence);
Toast.makeText(getApplicationContext(),
serverCalculatedHash, Toast.LENGTH_SHORT).show();
paymentParam.setMerchantHash(serverCalculatedHash);
// calculateServerSideHashAndInitiatePayment(paymentParam);
PayUmoneySdkInitilizer.startPaymentActivityForResult(TrayActivity.this, paymentParam);
public static String hashCal(String type, String str) {
byte[] hashseq = str.getBytes();
StringBuffer hexString = new StringBuffer();
try {
MessageDigest algorithm = MessageDigest.getInstance(type);
algorithm.reset();
algorithm.update(hashseq);
byte messageDigest[] = algorithm.digest();
for (int i = 0; i<messageDigest.length; i++) {
String hex = Integer.toHexString(0xFF &messageDigest[i]);
if (hex.length() == 1) { hexString.append("0"); }
hexString.append(hex);
}
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} return hexString.toString();
}
You use in the code:
.setTnxId("0nf7" + System.currentTimeMillis())
And then later:
String tnxId="0nf7" + System.currentTimeMillis();
Probably not the only problem, but do you really want to use two different values for these (the time may change between the two calls)? Didn't you want the same tnxId in both cases?
TransactionIdProvider.java:
import java.util.Locale;
public class TransactionIdProvider {
private final static String DEFAULT_PREFIX = "ID";
// Convenient prime number for incrementing the counter
private final static long ID_ADD = 0xF0AD; // "f*ck off and die"
// 64b counter with non-trivial start value
private static long idCounter = 0x0101F00DDEADBEEFL;
/**
* Returns ID consisting of prefix string and 64b counter interleaved
* with 32b per-4s-timestamp.
*
* May produce identical ID (collision) when:
* 1) class is reloaded within 4s
* (to fix: serialize "idCounter" upon shutdown/restart of VM, or
* modify prefix per start of VM)
* 2) more than 2^64 IDs are requested within 4s (no fix, unexpected)
* 3) more than 2^64 IDs are requested after cca. 550 years.
* (no fix, unexpected)
* 4) more than one static instance of TransactionIdProvider is used
* (two or more VMs running the app) (to fix put different prefix in
* every VM/server running this)
*
* Length of returned ID is prefix.length() + 24 alphanumeric symbols.
*/
public static synchronized String getNewId(final String prefix) {
idCounter += ID_ADD; // increment counter
// get 32b timestamp per ~4s (millis/4096) (good for ~550 years)
final int timeStamp = (int)(System.currentTimeMillis()>>12);
final int idPart1 = (int)(idCounter>>32);
final int idPart2 = (int)(idCounter);
return String.format(Locale.US, "%s%08X%08X%08X",
prefix, idPart1, timeStamp, idPart2);
}
public static String getNewId() {
return getNewId(DEFAULT_PREFIX);
}
}
Not sure how much usable is this one, and if the ID may be so long. Feel free to use/modify it any way you wish.
Also I wonder, whether I didn't forget about something important, but can't recall anything.
The security aspect of this one is still quite weak, as within 4s time span the ID will be like simple addition, but at least it's not producing 1, 2, 3... series.
Did found some SDK docs, looks like txnId may be 25 chars long, so you have 1 char for prefix only. Or cut down on timestamp, using %07X in format and masking value with 0x0FFFFFFF, that would make it repeat every ~34 years -> 2 letters for prefix. Or change counter to 32b int, should be still more than enough, unless you expect thousands of transactions per second -> that would remove 8 chars. Or base32/base64 the whole ID to shorten it (depends what alphabet is legal for content)...
Or whatever... already spent enough time with this. Hire a pro.
I'm trying to use UsageStatsManager to get the foreground app on a Nexus 5 with Marshmallow. I remember it used to work, but for some reason I'm getting null strings for package/class names now.
Here's my implementation
public String[] getForegroundPackageNameClassNameByUsageStats() {
String packageNameByUsageStats = null;
String classByUsageStats = null;
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
UsageStatsManager mUsageStatsManager = (UsageStatsManager)getSystemService("usagestats");
final long INTERVAL = 1000;
final long end = System.currentTimeMillis();
final long begin = end - INTERVAL;
final UsageEvents usageEvents = mUsageStatsManager.queryEvents(begin, end);
while (usageEvents.hasNextEvent()) {
UsageEvents.Event event = new UsageEvents.Event();
usageEvents.getNextEvent(event);
if (event.getEventType() == UsageEvents.Event.MOVE_TO_FOREGROUND) {
packageNameByUsageStats = event.getPackageName();
classByUsageStats = event.getClassName();
Log.d(TAG, "packageNameByUsageStats is" + packageNameByUsageStats + ", classByUsageStats is " + classByUsageStats);
}
}
}
return new String[]{packageNameByUsageStats,classByUsageStats};
}
For some reason, it doesn't go into the while loop, i.e. usageEvents.hasNextEvent() is false. Because of this, it returns null package/class names.
Any idea what I'm doing wrong?
Thanks.
OK, so I found that once I set the interval to 10000 instead of 1000, it works. Apparently a 1s interval is too small.
I am using this myself. I think the usage stats will only be updated when an app comes to foreground. So if the foreground app got to the foreground (and stayed) before your 'begin' timestamp then you will not get it. :(
On the other hand when you use a long time ago you will get a giant list where you only need the highest time to determine the foreground app.
So what I do is I create 3 different times: 1min ago, 1 hour ago and 12 hours ago.
When I get an empty list on 1min I repeat request with 1h and so on. That way I get foreground most of the time. But I never get it to work ALL of the time.
I really miss the old way of just asking the package manager which app is foreground (prior to android 5), the new way is a bit messy.
I use this code to get information of currently running applications in android app.
I want to how I can get timing information(start time) of currently running applications
long millisSinceBoot = SystemClock.elapsedRealtime();
System.out.println("00000 "+millisSinceBoot);
System.out.println("11111 "+values.get(position).activeSince+" "+values.get(position).process);
long time = ((millisSinceBoot - values.get(position).activeSince)/1000);
int[] vals = splitToComponentTimes(time);
String time1 = vals[0]+":"+vals[1]+":"+vals[2];
time_list.add(time);
timer.setText(time1);
System.out.println("valssssss "+vals[0]+" "+vals[1]);