如何仅更改 java.net.URL object 的协议部分？

Question

I have a java.net.URL object that uses the HTTPS protocol, eg:

https://www.bla.com

And I have to change only the protocol part of this URL object so that when I call its toString() method I get this:

http://www.bla.com

What is the best way to do that?

Answer 1

You'll have the use the methods available to you:

URL oldUrl = new URL("https://www.bla.com");
URL newUrl = new URL("http", oldUrl.getHost(), oldUrl.getPort(), oldUrl.getFile(), oldUrl.getRef());

There's an even more expansive set() method that takes 8 items, you might need that for more elaborate URLs.

Edit: As was just pointed out to me, I wasn't paying attention, and set() is protected. So URL is technically mutable, but to us mortals, it's immutable. So you'll just have to construct a new URL object.

Answer 2

You can also use string replacement:

URL oldUrl = new URL("https://www.bla.com");
String newUrlString = oldUrl.toString().replaceFirst("^https", "http");
URL newUrl = new URL(newUrlString);

Answer 3

Or you can use org.springframework.web.util.UriComponentsBuilder / org.springframework.web.util.UriComponents

see: Does there exist a mutable URL/URI object in Java?

Answer 4

It appears they forgot to make their class useful. Stealing code from URL.toExternalForm() helps:

public class ICantBelieveThisIsNotInTheStandardLibrary {
    public static final URL makeCopyWithDifferentProtocol(URL u, String protocol) {
        StringBuffer result = new StringBuffer();
        result.append(protocol);
        result.append(":");
        if (u.getAuthority() != null && u.getAuthority().length() > 0) {
            result.append("//");
            result.append(u.getAuthority());
        }
        if (u.getPath() != null) {
            result.append(u.getPath());
        }
        if (u.getQuery() != null) {
            result.append('?');
            result.append(u.getQuery());
        }
        if (u.getRef() != null) {
            result.append("#");
            result.append(u.getRef());
        }
        return new URL(result.toString());
    }
}

The answer which suggests to use a String-replacement is shorter, but you are going to need something like this if you ever want to change any of the other URL components.