从InputStream获取URL

Question

I'm wondering how InputStream in java is implemented from low level perspective.

Suppose I write a below java code for making connection with a website.

url = new URL("[some url info]");
URLConnection urlcon = url.openConnection();
InputStream in = urlcon.getInputStream();
while((readcount = in.read(buffer)) != -1){
        fos.write(buffer,0,readcount);

Could I know URL from InputStream("in" in the above code block) directly by casting it's type and call an appropriate method like below? Are there any other ways to get URL from InputStream?

(newtype) new = (newtype) in;
String Url = new.appropriatemethod();

I searched all subclasses of InputStream, but I couldn't find any classes which have a interface to give it's URL. ( https://docs.oracle.com/javase/7/docs/api/java/io/InputStream.html )

However, I think InputStream somehow have information of URL to receive data from a website which has this URL.

I might have big misunderstanding about "Stream".

Thank you for reading my quetion. :)

Answer 1

InputStream is just a stream not a URLConnection . When you type InputStream in = urlcon.getInputStream(); . You will get input stream not a url connection. When you type in.read then you are reading the Stream and not URLConnection .

An InputStream is a reference to source of data (be it a file, network connection etc), that we want to process as follows:

• we generally want to read the data as "raw bytes" and then write our own code to do something interesting with the bytes;

• we generally want to read the data in sequential order: that is, to get to the nth byte of data, we have to read all the preceding bytes first, and we're not guaranteed to be able to "jump back" again once we've read them.