Android：java.net.protocolException不支持输出

因此这个代码,使一个HttpPost请求具有一些参数：

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;
    }
}

但是我在代码中注释了这样的异常.

其实我正在使用AsyncTask从我的Activity中调用MConnections.PostData()两次.这可能会导致异常：已连接,但我正在使用connection.disconnect.但为什么我还会得到这个异常？

我用错了吗？

谢谢