为什么这有时不起作用？
con = (HttpURLConnection)(new URL(update).openConnection(proxy));
con.setInstanceFollowRedirects( false );
con.setConnectTimeout(60000);
con.setReadTimeout(60000);
con.connect();
我收到以下错误：
Exception in thread "main" java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.Socket.connect(Socket.java:579)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:432)
at sun.net.www.http.HttpClient$1.run(HttpClient.java:484)
at sun.net.www.http.HttpClient$1.run(HttpClient.java:482)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.http.HttpClient.privilegedOpenServer(HttpClient.java:481)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:522)
at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:275)
at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:371)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:975)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:153)
at app.main(app.java:108)