java - Android UnknownHostException Facebook SDK

Question

情况是这样的。我的应用程序运行良好，并且能够与 URL 建立连接。但是在让应用程序运行几个小时后，Facebook 请求突然给我以下错误。

09-26 10:01:25.175: W/System.err(252): java.net.UnknownHostException: Host is unresolved: xyz.com:80
09-26 10:01:25.175: W/System.err(252):  at java.net.Socket.connect(Socket.java:1037)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:62)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnectionManager$ConnectionPool.getHttpConnection(HttpConnectionManager.java:145)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnectionManager.getConnection(HttpConnectionManager.java:67)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnection.getHTTPConnection(HttpURLConnection.java:821)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:807)
09-26 10:01:25.175: W/System.err(252):  at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1051)
09-26 10:01:25.175: W/System.err(252):  at java.net.URL.openStream(URL.java:653)

此错误在应用程序和模拟器上都会发生。当我注销我的应用程序并重新连接到 Facebook 时，连接再次工作。

我应该注意:当我与自己的服务器建立连接时，没有出现问题。

此错误是由以下行引起的...

mAsyncFacebookRunner.request("fql", paramaters,
                new FQLRequestListener());

Answer 1

java.net.UnknownHostException 通常表示无法解析主机的 IP 地址，但实际原因可能因情况而异。如果代码实现正确(不管你使用的API是HttpUrlConnection还是DefaultHttpClient)，还是断断续续的发生，很可能是老Android系统的DNS缓存和TTL管理相关的bug:

Issue 7904: Android does not support TTL and caches DNS result for 10 minutes

自 Android 4.1 起已修复，请参阅 InetAddress API Doc 中的额外注释:

DNS caching

In Android 4.0 (Ice Cream Sandwich) and earlier, DNS caching was performed both by InetAddress and by the C library, which meant that DNS TTLs could not be honored correctly. In later releases, caching is done solely by the C library and DNS TTLs are honored.

对于旧的 Android 版本，Android 建议调整 Java 级别的 DNS 属性 networkaddress.cache.ttl 和 networkaddress.cache.negative.ttl，请参阅 old source code 中的 JavaDoc :

/**
 * ... ...
 *
 * <h4>DNS caching</h4>
 * <p>On Android, addresses are cached for 600 seconds (10 minutes) by default. Failed lookups are
 * cached for 10 seconds. The underlying C library or OS may cache for longer, but you can control
 * the Java-level caching with the usual {@code "networkaddress.cache.ttl"} and
 * {@code "networkaddress.cache.negative.ttl"} system properties. These are parsed as integer
 * numbers of seconds, where the special value 0 means "don't cache" and -1 means "cache forever".
 *
 * ... ...
 */

相关讨论:

• UnknownHostException in java (that too only sometimes)
• what is the purpose of Java level DNS caching?

如果您的目标是旧的 Android 版本，请尝试调整这两个属性，看看是否有任何不同。