What is the proper way of setting headers in a URLConnection?

问题

My code is like the following:

URLConnection cnx = address.openConnection();
cnx.setAllowUserInteraction(false);         
cnx.setDoOutput(true);
cnx.addRequestProperty("User-Agent", 
    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)");
InputStream is = cnx.getInputStream();

Is it ok if I set the headers before I get the InputStream? Will my header be sent, or will the server see the default URLConnection's user-agent ( if any ) ?

回答1:

The headers must be set prior to getting the InputStream to have any affect - an IllegalStateException will be thrown if the connection is already open.

As far as the User-Agent header specifically, it should be sent if it has been set.

See the URLConnection JavaDoc.

回答2:

To answer the question, the code is correct. The moment getInputStream(), an HTTP get is sent to the target server.

A side-note on user-agent, if you don't set it, URLConnection will send the default one anyway, which is:

User-Agent: Java/1.6.0_24 (varies depending on your java version)

回答3:

I'd advise against using low-level constructs such as URLConnection. There are plenty of libraries for sending HTTP requests, with the most prominent being Apache HTTP Client.

来源：https://stackoverflow.com/questions/331538/what-is-the-proper-way-of-setting-headers-in-a-urlconnection