how to check protocol present in url or not?

Question

how to check protocol is present in URL , if not present need to append it. is there any class to achieve this in java? eg: String URL = www.google.com

need to get http://www.google.com

Answer 1

Just use String.startsWith("http://") to check this.

public String ensure_has_protocol(final String a_url)
{
    if (!a_url.startsWith("http://"))
    {
        return "http://" + a_url;
    }
    return a_url;
}

EDIT:

An alternative would use a java.net.URL instance, whose constructor would throw an java.net.MalformedURLException if the URL did not contain a (legal) protocol (or was invalid for any other reason):

public URL make_url(final String a_url) throws MalformedURLException
{
    try
    {
        return new URL(a_url);
    }
    catch (final MalformedURLException e)
    {
    }
    return new URL("http://" + a_url);
}

You can use URL.toString() to obtain string representation of the URL. This is an improvement on the startsWith() approach as it guarantees that return URL is valid.

Answer 2

Let's say you have String url = www.google.com. String class methods would be enough for the goal of checking protocol identifiers. For example, url.startsWith("https://") would check whether a specific string is starting with the given protocol name.

However, are these controls enough for validation?

I think they aren't enough. First of all, you should define a list of valid protocol identifiers, e.g. a String array like {"http", "ftp", "https", ...}. Then you can parse your input String with regex ("://") and test your URL header whether it belongs to the list of valid protocol identifiers. And domain name validation methods are beyond this question, you can/should handle it with different techniques as well.

Answer 3

Just for completeness, I would do something like the following:

import com.google.common.base.Strings;

private static boolean isUrlHttps(String url){
    if(Strings.isNullOrEmpty(url))
        return false;
    return url.toLowerCase().startsWith("https://");
}