android - HttpsURLConnection 中的 "Connection already established"异常

Question

我正在尝试使用 HttpsURLConnection 执行 POST 请求，并获取

java.net.ProtocolException: Connection already established

关于 setRequestMethod 奇怪的是，conn.connected 之前返回 false。

我错过了什么？

URL url = new URL("https://ws.audioscrobbler.com/2.0/");
HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
conn.setReadTimeout(15000);
conn.setConnectTimeout(15000);
// here conn.connected is false
conn.setRequestMethod("POST"); // here I get java.net.ProtocolException: Connection already established
conn.setDoInput(true);

编辑

我试过 DefaultHttpClient 并且它有效，所以我将改用它。

Answer 1

对于遇到此问题的任何其他人，我遇到了一个操作顺序问题，该问题仅在我执行请求正文中包含内容的 HTTP POST 时才会影响到我。在 HttpURLConnection 实际发起与服务器的连接时，在所有情况下都不是完全清楚。

我最初的请求是这样的:

        HttpURLConnection conn = null;
        try
        {
            conn = (HttpURLConnection) baseUrl.openConnection();  
            conn.setConnectTimeout(connectTimeoutMillis);
            conn.setReadTimeout(requestTimeoutMillis);

            //required for reading a response body
            conn.setDoInput(true);

            //Not all request types have a body (e.g. GET usually doesn't)
            if(requestBody != null && requestBody.length > 0)
            {
                conn.setDoOutput(true);
                conn.setFixedLengthStreamingMode(requestBody.length);
                conn.getOutputStream().write(requestBody);
                conn.getOutputStream().flush();
                conn.getOutputStream().close();
            }

            try
            {
                conn.setRequestMethod(verb.toUpperCase());
            }
            catch (final ProtocolException e)
            {
                response.setError("Invalid HTTP verb \"" + verb + "\" received.","");
                Log.e(TAG, response.errorMessage, e);
                return response;
            }

事实证明，在调用“conn.getOutputStream()”之后，您不能再调用“conn.setRequestMethod(...)”，所以在我的例子中，简单的解决方法是调用“conn.setRequestMethod(. ..)”在处理写入请求正文之前。工作代码是:

HttpURLConnection conn = null;
        try
        {
            conn = (HttpURLConnection) baseUrl.openConnection();  
            conn.setConnectTimeout(connectTimeoutMillis);
            conn.setReadTimeout(requestTimeoutMillis);

            //required for reading a response body
            conn.setDoInput(true);

            try
            {
                conn.setRequestMethod(verb.toUpperCase());
            }
            catch (final ProtocolException e)
            {
                response.setError("Invalid HTTP verb \"" + verb + "\" received.","");
                Log.e(TAG, response.errorMessage, e);
                return response;
            }

            //Not all request types have a body (e.g. GET usually doesn't)
            if(requestBody != null && requestBody.length > 0)
            {
                conn.setDoOutput(true);
                conn.setFixedLengthStreamingMode(requestBody.length);
                conn.getOutputStream().write(requestBody);
                conn.getOutputStream().flush();
                conn.getOutputStream().close();
            }

唯一真正的变化只是切换了调用的顺序，从而消除了异常。希望这能为遇到此问题的任何其他人解决此问题。