android11系统开发之ntp服务器_android 开发 设置ntp

最近在项目中遇到了设备开机联网后不会主动更新时间的情况。由于上层app需要登录服务器，登录过程会对时间进行校验，时间不对服务器登录不成功。所以好好的研究了一下android的时间更新原理。具体原理不细说，网络上讲的很详细。针对项目来做一个简单的说明。
主要代码有：
/frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java
/frameworks/base/core/java/android/util/NtpTrustedTime.java
/frameworks/base/core/java/android/net/SntpClient.java
/frameworks/base/core/res/res/values/config.xml
针对项目中出现的问题，主要修改config.xml

   <!-- Remote server that can provide NTP responses. -->
-    <string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
+    <string translatable="false" name="config_ntpServer">ntp1.aliyun.com</string>
     <!-- Normal polling frequency in milliseconds -->
     <integer name="config_ntpPollingInterval">86400000</integer>
     <!-- Try-again polling interval in milliseconds, in case the network request failed -->
-    <integer name="config_ntpPollingIntervalShorter">60000</integer>
+    <integer name="config_ntpPollingIntervalShorter">30000</integer>
     <!-- Number of times to try again with the shorter interval, before backing
          off until the normal polling interval. A value < 0 indicates infinite. -->
-    <integer name="config_ntpRetry">3</integer>
+    <integer name="config_ntpRetry">5</integer>
     <!-- Timeout to wait for NTP server response in milliseconds. -->
     <integer name="config_ntpTimeout">5000</integer>
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测试了一下，原生的ntp服务器2.android.pool.ntp.org访问成功率是相对低一些，所以将config_ntpServer 改为国内ali的ntp1.aliyun.com（还有其他可选），请求时间间隔改短（value < 0 代表一直请求），retry次数增加。
还可以考虑在frameworks/base/core/java/android/util/NtpTrustedTime.java 中增加备用ntp服务器。
参考网上代码：

--- a/frameworks/base/core/java/android/util/NtpTrustedTime.java
+++ b/frameworks/base/core/java/android/util/NtpTrustedTime.java
@@ -98,6 +98,16 @@ public class NtpTrustedTime implements TrustedTime {
 
     private static NtpTrustedTime sSingleton;
 
+     String[] backupNtpServers = new String[]{
+               "ntp2.aliyun.com",
+               "ntp3.aliyun.com",
+               "ntp4.aliyun.com",
+               "ntp5.aliyun.com",
+               "ntp6.aliyun.com",
+       };
+       int index = -1;
+
     @NonNull
     private final Context mContext;
 
@@ -162,12 +172,21 @@ public class NtpTrustedTime implements TrustedTime {
 
             if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");
             final SntpClient client = new SntpClient();
-            final String serverName = connectionInfo.getServer();
+            // final String serverName = connectionInfo.getServer();
+            boolean result = false;
+            String serverName = connectionInfo.getServer();
             final int timeoutMillis = connectionInfo.getTimeoutMillis();
-            if (client.requestTime(serverName, timeoutMillis, network)) {
+            // if (client.requestTime(serverName, timeoutMillis, network)) {
+            while (!(result = client.requestTime(serverName, timeoutMillis, network)) && index < (backupNtpServers.length-1) ) {
+            index++;
+            serverName = backupNtpServers[index];
+            if (LOGD) Log.d(TAG, "-----------add--serverName--------"+serverName);
+            }
+            if(result){
                 long ntpCertainty = client.getRoundTripTime() / 2;
-                mTimeResult = new TimeResult(
-                        client.getNtpTime(), client.getNtpTimeReference(), ntpCertainty);
+                // mTimeResult = new TimeResult(
+                //         client.getNtpTime(), client.getNtpTimeReference(), ntpCertainty);
+                mTimeResult = new TimeResult(client.getNtpTime(), client.getNtpTimeReference(), ntpCertainty);
                 return true;
             } else {
                 return false;
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重新烧录后，时间更新成功率变高了。但是仍不能保证100%更新成功。这也是网络时间同步的缺陷。如果想要保证一定更新可以考虑增加rtc。