java - 未知主机异常

Question

这个问题已经有答案了:

Networking code sometimes throws UnknownHostException (4 个回答)

已关闭 3 年前。

为什么会抛出UnknownHostException？

    parameters = "user=akirus&pass=1234&version=1";
    String result = excutePost("http://russianimperial.ru/minecraft/loginServer.php", parameters);

  public static String excutePost(String targetURL, String urlParameters) {
      HttpURLConnection connection = null;
      try {
          URL url = new URL(targetURL);
          connection = (HttpURLConnection)url.openConnection();

          connection.setRequestMethod("POST");
          connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
          connection.setRequestProperty("Content-Length", Integer.toString(urlParameters.getBytes().length));
          connection.setRequestProperty("Content-Language", "en-US");

          connection.setUseCaches(false);
          connection.setDoInput(true);
          connection.setDoOutput(true);

          DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
          wr.writeBytes(urlParameters);
          wr.flush();
          wr.close();

          InputStream is = connection.getInputStream();
          BufferedReader rd = new BufferedReader(new InputStreamReader(is));

          StringBuffer response = new StringBuffer();
          String line;
          while ((line = rd.readLine()) != null) {
              response.append(line);
              response.append('\r');
          }
          rd.close();

          String str1 = response.toString();
          return str1;
     }catch (Exception e) {
         e.printStackTrace();
         return null;
     }finally {
         if (connection != null)
             connection.disconnect();
     }
  }

网址http://russianimperial.ru/minecraft/loginServer.php已验证。早些时候它工作得很好。 UnknownHostException扔在这个地方InputStream is = connection.getInputStream(); 。在javadoc中写道connection.getInputStream()当协议(protocol)不支持输入时可以抛出此异常，但我认为http支持输入。

Answer 1

事实上，这段代码会产生 UnknownHostException。但看一下完整的堆栈跟踪:

java.net.UnknownHostException: updaters
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:195)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at sun.net.NetworkClient.doConnect(NetworkClient.java:163)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:388)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:523)
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:227)
    at sun.net.www.http.HttpClient.New(HttpClient.java:300)
    at sun.net.www.http.HttpClient.New(HttpClient.java:317)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:970)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:911)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:836)
    at sun.net.www.protocol.http.HttpURLConnection.followRedirect(HttpURLConnection.java:2113)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1367)
    at Host.excutePost(Host.java:43)
    at Host.main(Host.java:14)

当 URL 连接尝试重定向时，您会遇到此异常，并且重定向会转到一些不清楚的“更新程序”。所以它不是“Russianimperials.ru”，而是它所做的重定向。为什么？这取决于页面，-您也可能在传递参数的方式上做错了什么。