URLConnection开放怪异

Question

很难理解URLConnection以及可能隐式调用connect（）的地方。

此代码无效：

URL url = new URL(firstUrl);
HttpURLConnection connection = (HttpURLConnection) obj.openConnection();
conn.getHeaderField("Location"); //returns null
connection.setInstanceFollowRedirects(false);

此代码有效：

URL url = new URL(firstUrl);
HttpURLConnection connection = (HttpURLConnection) obj.openConnection();
connection.setInstanceFollowRedirects(false);
conn.getHeaderField("Location"); //returns the redirect URL

我很难理解这一点。是＆＃34; getHeaderField＆＃34;隐式调用连接？我在任何地方都没有看到文档中提到的内容。

Answer 1

它确实连接了，请参阅http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/sun/net/www/protocol/http/HttpURLConnection.java#HttpURLConnection.getHeaderField%28java.lang.String%29 应该在文档中提到，我同意......