Java URL 类 openStream 抛出 java.net.ConnectException : Connection refused: connect

Question

我正在尝试编写一个简单的程序来显示各种 URL 的内容。我的代码是这样的。

    import java.io.IOException;
    import java.io.InputStream;
    import java.net.*;

    public class test {
public static void main(String[] args) {
    URL url;
    //String site ="ftp://ftp.suse.com/";
    //String site ="http://www.google.ca";
    //String site = "ftp://ftp.gnu.org/README";
    String site = "ftp://metalab.unc.edu/";
    try {
        url = new URL(site);
        InputStream stream = url.openStream();
        for(int i = 0;i!= -1;i= stream.read()){
            System.out.print((char)i);
        }
        stream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

前 3 个资源很好

• 字符串站点 ="ftp://ftp.suse.com/"；
• 字符串站点 =“http://www.google.ca”；
• String site = "ftp://ftp.gnu.org/README";

但是最后一个

• 字符串站点 =“ftp://metalab.unc.edu/”；

产生以下错误

    java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at sun.net.ftp.impl.FtpClient.openPassiveDataConnection(Unknown Source)
at sun.net.ftp.impl.FtpClient.openDataConnection(Unknown Source)
at sun.net.ftp.impl.FtpClient.list(Unknown Source)
at sun.net.www.protocol.ftp.FtpURLConnection.getInputStream(Unknown Source)
at java.net.URL.openStream(Unknown Source)
at test.main(test.java:13)

我尝试过的其他各种 ftp 站点也会发生这种情况。 HTTP 站点没有遇到任何问题。有什么想法可以解决这个问题。我可以从浏览器访问的所有指定资源。

Answer 1

该网站可能是refusing non-browser user agents 。您可以尝试设置用户代理:

URL url;
String site = "ftp://metalab.unc.edu/";
try {
    url = new URL(site);
    URLConnection urlc = url.openConnection();
    urlc.addRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0a2) Gecko/20110613 Firefox/6.0a2");
    InputStream stream = urlc.getInputStream();
    for(int i = 0;i!= -1;i= stream.read()){
        System.out.print((char)i);
    }
    stream.close();
} catch (IOException e) {
    e.printStackTrace();
}