我以前使用的是 HttpClient 和 BasicNameValuePairs，由于某些原因我不得不转向 HttpUrlConnection。

因此，这段代码使用特定参数发出 HttpPost 请求:

public class MConnections {

    static String BaseURL = "http://www.xxxxxxxxx.com";
    static String charset = "UTF-8";
    private static String result;
    private static StringBuilder sb;
    private static List<String> cookies = new ArrayList<String>();

    public static String PostData(String url, String sa[][]) {

        HttpURLConnection connection = null;
        try {
            connection = (HttpURLConnection) new URL(BaseURL + url)
                    .openConnection();
        } catch (MalformedURLException e1) {
        } catch (IOException e1) {
        }

        cookies = connection.getHeaderFields().get("Set-Cookie");
        try{
        connection.setDoOutput(true); // Triggers POST.
        connection.setRequestProperty("Accept-Charset", charset);
        connection.setRequestProperty("Content-Type",
                "application/x-www-form-urlencoded;charset=" + charset);
        }catch (Exception e) {

            //Here i get Exception that "java.lang.IllegalStateException: Already connected"
        }
        OutputStream output = null;
        String query = "";
        int n = sa.length;
        for (int i = 0; i < n; i++) {
            try {
                query = query + sa[i][0] + "="
                        + URLEncoder.encode(sa[i][1], "UTF-8");
            } catch (UnsupportedEncodingException e) {
            }
        }
        try {
            output = connection.getOutputStream();
            output.write(query.getBytes(charset));
        } catch (Exception e) {

            //Here i get Exception that "android: java.net.protocolException: Does not support output"
        } finally {

            if (output != null)
                try {
                    output.close();
                } catch (IOException e) {
                }
        }
        InputStream response = null;
        try {
            response = connection.getInputStream();
        } catch (IOException e) {

            //Here i get Exception that "java.io.IOException: BufferedInputStream is closed"
        } finally {

            //But i am closing it here
            connection.disconnect();
        }
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    response, "iso-8859-1"), 8);
            sb = new StringBuilder();
            sb.append(reader.readLine());
            String line = "0";
            while ((line = reader.readLine()) != null) {
                sb.append("\n" + line);
            }
            response.close();
            result = sb.toString();
        } catch (Exception e) {
        }
        return result;
    }
}

但是我在代码中得到了这样的异常。

实际上，我使用 AsyncTask 从我的 Activity 调用了两次 MConnections.PostData()。这可能会导致异常:已连接，但我正在使用connection.disconnect。但为什么我仍然得到那个异常？

我是不是用错了？

谢谢

最佳答案

对于协议(protocol)异常，尝试在调用 getOutputStream() 之前添加以下内容:

connection.setDoOutput(true);

感谢 Brian Roach 在这里的回答，发现了这个答案:https://stackoverflow.com/a/14026377/387781

旁注:我在运行 Gingerbread 的 HTC Thunderbolt 上遇到了这个问题，但在运行 Jelly Bean 的 Nexus 4 上却没有。

关于Android: java.net.protocolException 不支持输出，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13247836/