java - 真的有必要使用 url.openConnection() 吗？

Question

众所周知，这两个代码会产生相同的结果

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);
    }
}

和

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);
    }
}

那么使用 google.openConnection() 有什么意义呢？

Answer 1

可能是此方法的 javadoc 帮助:

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.

如果您想为您的连接添加一些特定的连接属性，请使用它。

例如:

URLConnection urlConnection = google.openConnection();

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