是否真的有必要使用url.openConnection（）？

Question

As we all know both these codes will yield the same result

public class MainApp {
    public static void main(String[] args) throws IOException {
        URL google = new URL("http://www.google.com");
        google.openConnection();
        BufferedReader reader = new BufferedReader(new InputStreamReader(google.openStream()));
        reader.lines().forEach(System.out::println);
    }
}

and

public class MainApp {
    public static void main(String[] args) throws IOException {
        URL google = new URL("http://www.google.com");
        BufferedReader reader = new BufferedReader(new InputStreamReader(google.openStream()));
        reader.lines().forEach(System.out::println);
    }
}

So what's the point in using google.openConnection()?

Answer 1

May be javadoc for this method helps:

public java.net.URLConnection openConnection() throws java.io.IOException

Returns a URLConnection instance that represents a connection to the remote object referred to by the URL . A new instance of URLConnection is created every time when invoking the URLStreamHandler.openConnection(URL) method of the protocol handler for this URL.

It should be noted that a URLConnection instance does not establish the actual network connection on creation. This will happen only when calling URLConnection.connect() .

If for the URL 's protocol (such as HTTP or JAR), there exists a public, specialized URLConnection subclass belonging to one of the following packages or one of their subpackages: java.lang , java.io , java.util , java.net , the connection returned will be of that subclass. For example, for HTTP an HttpURLConnection will be returned, and for JAR a JarURLConnection will be returned.

Use this if you want to add some specific connectivity properties to your connection.

For example:

URLConnection urlConnection = google.openConnection();

urlConnection.setReadTimeout(1000);
urlConnection.setConnectTimeout(1000);

Answer 2

Since the code for openStream() is:

public final InputStream openStream() throws java.io.IOException {
    return openConnection().getInputStream();
}

It seems quite redundant indeed.

But if I were you, if I openConnection() d, I would then get the InputStream on the returned URLConnection .

Answer 3

openConnection() does not modify the URL object, it returns a URLConnection instance that you could then use. The code in the question ignores the return value of openConnection() , so, in this case, it's indeed pointless. it would only be useful if you actually do something with this connection object, such as, eg, modifying its timeout:

URL google = new URL("http://www.google.com");
URLConnection conn = google.openConnection();
conn.setTimeout(7); // just an example 
BufferedReader reader = 
    new BufferedReader(new InputStreamReader(conn.getInputStream()));
reader.lines().forEach(System.out::println);