Get header from HttpUrlConnection object

问题:

I want to send request to servlet and read headers from response. So I try it using this:

  URL url = new URL(contextPath + "file_operations");
    HttpURLConnection conn = null;
    try {
        conn = (HttpURLConnection) url.openConnection();
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("charset", "utf-8");
        conn.setUseCaches(false);
        conn.setConnectTimeout(1000 * 5);
        conn.connect();

        conn.getHeaderField("MyHeader")
        .....

But received headers are always null. Servlet works fine (i tried work with servlet using standalone HTTP client)

回答1:

Make sure you are getting the successful response before you try to fetch the headers. This is how you can check for your response:

int status = conn.getResponseCode();

if (status == HttpURLConnection.HTTP_OK) {
          String = conn.getHeaderField("MyHeader");

    }

Also make sure the Servlet response is not a redirect response, if redirected all the session information, including headers will be lost.

回答2:

Before the connect (right after setRquestPropert, setDoOutput a.s.o):

for (Map.Entry<String, List<String>> entries : conn.getRequestProperties().entrySet()) {    
    String values = "";
    for (String value : entries.getValue()) {
        values += value + ",";
    }
    Log.d("Request", entries.getKey() + " - " +  values );
}

Before disconnect (after reading response a.s.o):

for (Map.Entry<String, List<String>> entries : conn.getHeaderFields().entrySet()) {
    String values = "";
    for (String value : entries.getValue()) {
        values += value + ",";
    }
    Log.d("Response", entries.getKey() + " - " +  values );
}