ConnectException：操作超時

Question

我有以下類打開套接字連接來查詢WHOIS服務器。 不幸的是，每次我運行它（例如java WHOIS google.com）時，它總是拋出異常：

Contacting the WHOIS server for 'google.com' at whois.internic.net:43
Exception in thread "main" java.net.ConnectException: Operation timed out
    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:432)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:189)
    at WHOIS.performWhoisQuery(WHOIS.java:11)
    at WHOIS.main(WHOIS.java:28)

問題似乎是連接超時，我嘗試將超時設置為更長的值（例如5000）並且它不起作用。 它與代理和/或防火牆有關嗎？ 我整天都陷入困境。

public class WHOIS {
    public static void performWhoisQuery(String host, int port, String query) throws Exception {
        System.out.println(" Contacting the WHOIS server for '" + query + "' at " + host + ":" + port);

        Socket socket = new Socket(host, port);

        InputStreamReader isr = new InputStreamReader(socket.getInputStream());
        BufferedReader br = new BufferedReader(isr);

        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        out.println(query);

        String aLine = "";
        while ((aLine = br.readLine()) != null) {
            System.out.println(aLine);
        }
    }

    public static void main(String[] args) throws Exception {
        String domainNameToCheck = args[0];
        performWhoisQuery("whois.internic.net", 43, domainNameToCheck);

    }

}

Answer 1

檢查是否是防火牆問題的一種簡單方法是使用telnet從同一台計算機連接到目標主機/端口。

例如，在我的Linux機器上：

 aix@aix:~$ telnet whois.internic.net 43 Trying 199.7.57.74... Connected to whois.internic.net. Escape character is '^]'. 

如果您能夠連接，那么問題在於您的Java程序。 否則問題出在其他地方（防火牆等）。