连接超时。为什么？

Question

运行此代码时出现异常。为什么？线程“主”中的异常java.net.ConnectException：连接超时：connectimport java.io.BufferedReader;import java.io.InputStreamReader;import java.net.URL;public class MainClass {  public static void main(String[] args) throws Exception {    System.setProperty("java.protocol.handler.pkgs", "com.sun.net.ssl.internal.www.protocol");    URL url = new URL("https://www.verisign.com/");    BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));    String line;    while ((line = in.readLine()) != null) {      System.out.println(line);    }    in.close();  }}例外：Exception in thread "main" java.net.ConnectException: Connection timed out: connect    at java.net.PlainSocketImpl.socketConnect(Native Method)    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)    at java.net.Socket.connect(Socket.java:525)    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:550)    at com.sun.net.ssl.internal.ssl.BaseSSLSocketImpl.connect(BaseSSLSocketImpl.java:141)    at sun.net.NetworkClient.doConnect(NetworkClient.java:163)    at sun.net.www.http.HttpClient.openServer(HttpClient.java:394)    at sun.net.www.http.HttpClient.openServer(HttpClient.java:529)    at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:272)    at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:329)    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:172)    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:801)