我正在尝试获取应用程序中当前使用的DNS服务器的地址，无论是通过Wifi还是移动网络连接。 DhcpInfo对象应该提供此信息，但我如何获得有效的DhcpInfo对象？
8个回答
27
调用getRuntime().exec可能会导致应用程序挂起。
android.net.NetworkUtils.runDhcp()会导致不必要的网络请求。
所以我更喜欢这样做：
Class<?> SystemProperties = Class.forName("android.os.SystemProperties");
Method method = SystemProperties.getMethod("get", new Class[] { String.class });
ArrayList<String> servers = new ArrayList<String>();
for (String name : new String[] { "net.dns1", "net.dns2", "net.dns3", "net.dns4", }) {
String value = (String) method.invoke(null, name);
if (value != null && !"".equals(value) && !servers.contains(value))
servers.add(value);
}
- A-IV
5
21
不幸的是，大多数提供的解决方案在Android 8.0上已经无法使用了。
官方的Android文档在文章“Android 8.0行为变化”中非常清楚地说明了这一点。系统属性net.dns1、net.dns2、net.dns3和net.dns4不再可用，这一改变可以提高平台的隐私保护。
https://developer.android.com/about/versions/oreo/android-8.0-changes.html#o-pri
Dnsjava库也受到影响，dnsjava中使用的检测方法没有意识到Oreo的更改。
Varun Anand的解决方案在Oreo上工作，但存在处理与默认路由连接的弱点。因此，结果可能会被无效的DNS服务器污染，并且调用者可能会花费很多时间迭代列表并尝试连接到无法访问的DNS服务器。这在我的解决方案中得到了修复。Varun Anand解决方案的另一个问题是，它仅适用于API 21及以上版本。但是我必须说，这对我来说是个宝藏，让我能够编写自己的解决方案。所以谢谢！
为了方便起见，我提供了一个完整的DNS服务器检测类，您可以在任何Android版本上使用。完整的注释包括了回答为什么和如何的内容。
/**
* DNS servers detector
*
* IMPORTANT: don't cache the result.
*
* Or if you want to cache the result make sure you invalidate the cache
* on any network change.
*
* It is always better to use a new instance of the detector when you need
* current DNS servers otherwise you may get into troubles because of invalid/changed
* DNS servers.
*
* This class combines various methods and solutions from:
* Dnsjava http://www.xbill.org/dnsjava/
* Minidns https://github.com/MiniDNS/minidns
*
* Unfortunately both libraries are not aware of Orero changes so new method was added to fix this.
*
* Created by Madalin Grigore-Enescu on 2/24/18.
*/
public class DnsServersDetector {
private static final String TAG = "DnsServersDetector";
/**
* Holds some default DNS servers used in case all DNS servers detection methods fail.
* Can be set to null if you want caller to fail in this situation.
*/
private static final String[] FACTORY_DNS_SERVERS = {
"8.8.8.8",
"8.8.4.4"
};
/**
* Properties delimiter used in exec method of DNS servers detection
*/
private static final String METHOD_EXEC_PROP_DELIM = "]: [";
/**
* Holds context this was created under
*/
private Context context;
//region - public //////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////
/**
* Constructor
*/
public DnsServersDetector(Context context) {
this.context = context;
}
/**
* Returns android DNS servers used for current connected network
* @return Dns servers array
*/
public String [] getServers() {
// Will hold the consecutive result
String[] result;
// METHOD 1: old deprecated system properties
result = getServersMethodSystemProperties();
if (result != null && result.length > 0) {
return result;
}
// METHOD 2 - use connectivity manager
result = getServersMethodConnectivityManager();
if (result != null && result.length > 0) {
return result;
}
// LAST METHOD: detect android DNS servers by executing getprop string command in a separate process
// This method fortunately works in Oreo too but many people may want to avoid exec
// so it's used only as a failsafe scenario
result = getServersMethodExec();
if (result != null && result.length > 0) {
return result;
}
// Fall back on factory DNS servers
return FACTORY_DNS_SERVERS;
}
//endregion
//region - private /////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////
/**
* Detect android DNS servers by using connectivity manager
*
* This method is working in android LOLLIPOP or later
*
* @return Dns servers array
*/
private String [] getServersMethodConnectivityManager() {
// This code only works on LOLLIPOP and higher
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
try {
ArrayList<String> priorityServersArrayList = new ArrayList<>();
ArrayList<String> serversArrayList = new ArrayList<>();
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(CONNECTIVITY_SERVICE);
if (connectivityManager != null) {
// Iterate all networks
// Notice that android LOLLIPOP or higher allow iterating multiple connected networks of SAME type
for (Network network : connectivityManager.getAllNetworks()) {
NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
if (networkInfo.isConnected()) {
LinkProperties linkProperties = connectivityManager.getLinkProperties(network);
List<InetAddress> dnsServersList = linkProperties.getDnsServers();
// Prioritize the DNS servers for link which have a default route
if (linkPropertiesHasDefaultRoute(linkProperties)) {
for (InetAddress element: dnsServersList) {
String dnsHost = element.getHostAddress();
priorityServersArrayList.add(dnsHost);
}
} else {
for (InetAddress element: dnsServersList) {
String dnsHost = element.getHostAddress();
serversArrayList.add(dnsHost);
}
}
}
}
}
// Append secondary arrays only if priority is empty
if (priorityServersArrayList.isEmpty()) {
priorityServersArrayList.addAll(serversArrayList);
}
// Stop here if we have at least one DNS server
if (priorityServersArrayList.size() > 0) {
return priorityServersArrayList.toArray(new String[0]);
}
} catch (Exception ex) {
Log.d(TAG, "Exception detecting DNS servers using ConnectivityManager method", ex);
}
}
// Failure
return null;
}
/**
* Detect android DNS servers by using old deprecated system properties
*
* This method is NOT working anymore in Android 8.0
* Official Android documentation state this in the article Android 8.0 Behavior Changes.
* The system properties net.dns1, net.dns2, net.dns3, and net.dns4 are no longer available,
* a change that improves privacy on the platform.
*
* https://developer.android.com/about/versions/oreo/android-8.0-changes.html#o-pri
* @return Dns servers array
*/
private String [] getServersMethodSystemProperties() {
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
// This originally looked for all lines containing .dns; but
// http://code.google.com/p/android/issues/detail?id=2207#c73
// indicates that net.dns* should always be the active nameservers, so
// we use those.
final String re1 = "^\\d+(\\.\\d+){3}$";
final String re2 = "^[0-9a-f]+(:[0-9a-f]*)+:[0-9a-f]+$";
ArrayList<String> serversArrayList = new ArrayList<>();
try {
Class SystemProperties = Class.forName("android.os.SystemProperties");
Method method = SystemProperties.getMethod("get", new Class[]{String.class});
final String[] netdns = new String[]{"net.dns1", "net.dns2", "net.dns3", "net.dns4"};
for (int i = 0; i < netdns.length; i++) {
Object[] args = new Object[]{netdns[i]};
String v = (String) method.invoke(null, args);
if (v != null && (v.matches(re1) || v.matches(re2)) && !serversArrayList.contains(v)) {
serversArrayList.add(v);
}
}
// Stop here if we have at least one DNS server
if (serversArrayList.size() > 0) {
return serversArrayList.toArray(new String[0]);
}
} catch (Exception ex) {
Log.d(TAG, "Exception detecting DNS servers using SystemProperties method", ex);
}
}
// Failed
return null;
}
/**
* Detect android DNS servers by executing getprop string command in a separate process
*
* Notice there is an android bug when Runtime.exec() hangs without providing a Process object.
* This problem is fixed in Jelly Bean (Android 4.1) but not in ICS (4.0.4) and probably it will never be fixed in ICS.
* https://dev59.com/hmoy5IYBdhLWcg3wPLn0#11362081
*
* @return Dns servers array
*/
private String [] getServersMethodExec() {
// We are on the safe side and avoid any bug
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
try {
Process process = Runtime.getRuntime().exec("getprop");
InputStream inputStream = process.getInputStream();
LineNumberReader lineNumberReader = new LineNumberReader(new InputStreamReader(inputStream));
Set<String> serversSet = methodExecParseProps(lineNumberReader);
if (serversSet != null && serversSet.size() > 0) {
return serversSet.toArray(new String[0]);
}
} catch (Exception ex) {
Log.d(TAG, "Exception in getServersMethodExec", ex);
}
}
// Failed
return null;
}
/**
* Parse properties produced by executing getprop command
* @param lineNumberReader
* @return Set of parsed properties
* @throws Exception
*/
private Set<String> methodExecParseProps(BufferedReader lineNumberReader) throws Exception {
String line;
Set<String> serversSet = new HashSet<String>(10);
while ((line = lineNumberReader.readLine()) != null) {
int split = line.indexOf(METHOD_EXEC_PROP_DELIM);
if (split == -1) {
continue;
}
String property = line.substring(1, split);
int valueStart = split + METHOD_EXEC_PROP_DELIM.length();
int valueEnd = line.length() - 1;
if (valueEnd < valueStart) {
// This can happen if a newline sneaks in as the first character of the property value. For example
// "[propName]: [\n…]".
Log.d(TAG, "Malformed property detected: \"" + line + '"');
continue;
}
String value = line.substring(valueStart, valueEnd);
if (value.isEmpty()) {
continue;
}
if (property.endsWith(".dns") || property.endsWith(".dns1") ||
property.endsWith(".dns2") || property.endsWith(".dns3") ||
property.endsWith(".dns4")) {
// normalize the address
InetAddress ip = InetAddress.getByName(value);
if (ip == null) continue;
value = ip.getHostAddress();
if (value == null) continue;
if (value.length() == 0) continue;
serversSet.add(value);
}
}
return serversSet;
}
/**
* Returns true if the specified link properties have any default route
* @param linkProperties
* @return true if the specified link properties have default route or false otherwise
*/
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
private boolean linkPropertiesHasDefaultRoute(LinkProperties linkProperties) {
for (RouteInfo route : linkProperties.getRoutes()) {
if (route.isDefaultRoute()) {
return true;
}
}
return false;
}
//endregion
}
- Grigore Madalin
6
1这个救了我。对于将来使用dnsjava的任何人，在ResolverConfig.findAndroid中调用此例程，将结果添加到lserver列表中。 - urSus
这将始终返回所有活动连接的所有DNS服务器。如果您在WiFi网络上，而蜂窝连接仍然处于活动状态，则会返回两个连接的DNS服务器，但只有WiFi连接的服务器有效。 - Chrissi
如何使用这个类？ - zeleven
connectivityManager.getNetworkInfo已经过时。我尝试使用NetworkCallbacks来解决获取dns的问题。 - Manikandan
@Manikandan，如果您能做到，请提供解决方案，这样我就可以编辑我的答案并包含您的研究。我也会研究您在此处写的内容，并尝试更新我的代码（如果有必要）。 - Grigore Madalin
getprop不再返回.dns属性。在Android 10上进行了检查。 - Hsilgos13
android.net.ConnectivityManager会使用getAllNetworkInfo()方法向您提供一系列的NetworkInfo。然后，您可以使用android.net.NetworkUtils.runDhcp()方法获取给定网络接口的DhcpInfo - DhcpInfo结构体包含该接口的dns1和dns2的IP地址（这些是表示IP地址的整数值）。
如果你想知道如何将整数转换成IP地址，你可以这样做：
/**
* Convert int IP adress to String
* cf. http://teneo.wordpress.com/2008/12/23/java-ip-address-to-integer-and-back/
*/
private String intToIp(int i) {
return ( i & 0xFF) + "." +
(( i >> 8 ) & 0xFF) + "." +
(( i >> 16 ) & 0xFF) + "." +
(( i >> 24 ) & 0xFF);
}
编辑
你也可以通过类似下面的方式获取一个DchcpInfo对象：
WiFiManager wifi = (WifiManager) getSystemService(WIFI_SERVICE);
DhcpInfo info = wifi.getDhcpInfo();
- Cristian
3
1但是android.net.NetworkUtils.runDhcp()不是本地函数吗？我该如何访问它？ - John
8从Wifi获取DhcpInfo很简单，但是如何在移动网络（如UMTS）上实现呢？
我是否需要加载一些本地库才能访问android.net.NetworkUtils.runDhcp()？ - John
@John - 我已经发布了适用于移动网络的本地解决方案。看一下。 - Grimmace
11
以下代码适用于API 21及以上版本。它可以返回WiFi和移动数据接口的正确DNS服务器地址。我已使用shell实用程序"getprop"验证了所返回数值的正确性。
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
for (Network network : connectivityManager.getAllNetworks()) {
NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
if (networkInfo.isConnected()) {
LinkProperties linkProperties = connectivityManager.getLinkProperties(network);
Log.d("DnsInfo", "iface = " + linkProperties.getInterfaceName());
Log.d("DnsInfo", "dns = " + linkProperties.getDnsServers());
return linkProperties.getDnsServers();
}
}
- AllThatICode
1
这是一个为我提供自己的解决方案的宝藏，可以处理所有版本。请检查我的答案。再次感谢！ - Grigore Madalin
2
一种本地的替代方案是：
char dns1[PROP_VALUE_MAX];
__system_property_get("net.dns1", dns1);
或者更好的做法是提供一份全面的清单：
for (i = 1; i <= MAX_DNS_PROPERTIES; i++) {
char prop_name[PROP_NAME_MAX];
snprintf(prop_name, sizeof(prop_name), "net.dns%d", i);
__system_property_get(prop_name, dns);
}
这种方法有几个优点：
- runDHCP非常慢。它可能需要5-10秒钟的时间。如果使用不当，这可能会导致主要的挂起。
- runDCHP对3G/4G似乎无效。
- 由于runDCHP是一个隐藏的API，因此它可能会发生变化。事实上，在ICS中已经发生了变化。在ICS中，它采用了新的DhcpInfoInternal，因此您必须创建两个不同的来支持所有手机。
- Grimmace
1
6Android L中已经移除了__system_property_get()函数。 - Ales Teska
2
我建议在Android上进行复杂的DNS使用时使用dnsjava。让我们看看dnsjava如何确定连接的当前活动DNS服务器。从dnsjava ResolverConfig.java:428中可以看到：
/**
* Parses the output of getprop, which is the only way to get DNS
* info on Android. getprop might disappear in future releases, so
* this code comes with a use-by date.
*/
private void
findAndroid() {
// This originally looked for all lines containing .dns; but
// http://code.google.com/p/android/issues/detail?id=2207#c73
// indicates that net.dns* should always be the active nameservers, so
// we use those.
String re1 = "^\\d+(\\.\\d+){3}$";
String re2 = "^[0-9a-f]+(:[0-9a-f]*)+:[0-9a-f]+$";
try {
ArrayList lserver = new ArrayList();
ArrayList lsearch = new ArrayList();
String line;
Process p = Runtime.getRuntime().exec("getprop");
InputStream in = p.getInputStream();
InputStreamReader isr = new InputStreamReader(in);
BufferedReader br = new BufferedReader(isr);
while ((line = br.readLine()) != null ) {
StringTokenizer t = new StringTokenizer(line, ":");
String name = t.nextToken();
if (name.indexOf( "net.dns" ) > -1) {
String v = t.nextToken();
v = v.replaceAll("[ \\[\\]]", "");
if ((v.matches(re1) || v.matches(re2)) &&
!lserver.contains(v))
lserver.add(v);
}
}
configureFromLists(lserver, lsearch);
} catch ( Exception e ) {
// ignore resolutely
}
}
- Flow
1
警告：此代码可能导致Runtime.getRuntime().exec()中的挂起。 - Nappy
1
首先将layoutlib.jar添加到您的构建路径中，该文件位于$SDK_PATH/platforms/android-xxx/data/。
String dnsStr1 = android.os.SystemProperties.get("net.dns1");
String dnsStr2 = android.os.SystemProperties.get("net.dns2");
您还可以使用 $getprop 命令在 adb shell 中查看所有属性。
- c0ming
-2
您可以使用Java反射。例如：
ConnectivityManager mgr =
(ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
Method getLinkPropeties;
try{
getLinkPropeties = mgr.getClass().getMethod("getLinkProperties", int.class);
}catch (InvocationTargetException e) {
e.printStackTrace();
}
- zjg
网页内容由stack overflow 提供, 点击上面的可以查看英文原文，
原文链接
原文链接
android.os.SystemProperties并使用public static String get(String key, String def)。 - Arnaud CourtecuissemDNS吗？ - Varun