我试着上传一些字符串到服务器。当我试着上传到服务器时，字符串：

HttpResponse response = httpclient.execute(httppost);

我遇到了错误org.apache.http.client.ClientProtocolException.所有代码：

public void sendString(String stringToSend) {

    try {
        DefaultHttpClient httpclient = new DefaultHttpClient();
        httpclient.getCredentialsProvider().setCredentials(AuthScope.ANY, new UsernamePasswordCredentials(username, password));
        HttpPost httppost = new HttpPost(serverAddress);
        InputStreamEntity reqEntity = new InputStreamEntity( new ByteArrayInputStream(stringToSend.getBytes()), stringToSend.length());
        reqEntity.setContentType("application/xml");
        httppost.setEntity(reqEntity);
        HttpResponse response = httpclient.execute(httppost);
        if (response.getStatusLine().getStatusCode() != org.apache.http.HttpStatus.SC_OK) {
            Log.i("SEND", "not send "+response.getStatusLine());
        }else{
            Log.i("SEND", "send ok "+response.getStatusLine());
        }
    } catch (IOException e) {
        Log.w("IOException", e.toString() +" "+ e.getMessage());
    }        
}