Validating URL in Java

user_193742 0
Viewed 185253

I wanted to know if there is any standard APIs in Java to validate a given URL? I want to check both if the URL string is right i.e. the given protocol is valid and then to check if a connection can be established.

I tried using HttpURLConnection, providing the URL and connecting to it. The first part of my requirement seems to be fulfilled but when I try to perform HttpURLConnection.connect(), 'java.net.ConnectException: Connection refused' exception is thrown.

Can this be because of proxy settings? I tried setting the System properties for proxy but no success.

Let me know what I am doing wrong.

validation url java
11 Answers

Just important to point that the URL object handle both validation and connection. Then, only protocols for which a handler has been provided in sun.net.www.protocol are authorized (file, ftp, gopher, http, https, jar, mailto, netdoc) are valid ones. For instance, try to make a new URL with the ldap protocol:

new URL("ldap://myhost:389")

You will get a java.net.MalformedURLException: unknown protocol: ldap.

You need to implement your own handler and register it through URL.setURLStreamHandlerFactory(). Quite overkill if you just want to validate the URL syntax, a regexp seems to be a simpler solution.

user_2565610

I think the best response is from the user @b1nary.atr0phy. Somehow, I recommend combine the method from the b1nay.atr0phy response with a regex to cover all the possible cases.

public static final URL validateURL(String url, Logger logger) {

        URL u = null;
        try {  
            Pattern regex = Pattern.compile("(?i)^(?:(?:https?|ftp)://)(?:\\S+(?::\\S*)?@)?(?:(?!(?:10|127)(?:\\.\\d{1,3}){3})(?!(?:169\\.254|192\\.168)(?:\\.\\d{1,3}){2})(?!172\\.(?:1[6-9]|2\\d|3[0-1])(?:\\.\\d{1,3}){2})(?:[1-9]\\d?|1\\d\\d|2[01]\\d|22[0-3])(?:\\.(?:1?\\d{1,2}|2[0-4]\\d|25[0-5])){2}(?:\\.(?:[1-9]\\d?|1\\d\\d|2[0-4]\\d|25[0-4]))|(?:(?:[a-z\\u00a1-\\uffff0-9]-*)*[a-z\\u00a1-\\uffff0-9]+)(?:\\.(?:[a-z\\u00a1-\\uffff0-9]-*)*[a-z\\u00a1-\\uffff0-9]+)*(?:\\.(?:[a-z\\u00a1-\\uffff]{2,}))\\.?)(?::\\d{2,5})?(?:[/?#]\\S*)?$");
            Matcher matcher = regex.matcher(url);
            if(!matcher.find()) {
                throw new URISyntaxException(url, "La url no está formada correctamente.");
            }
            u = new URL(url);  
            u.toURI(); 
        } catch (MalformedURLException e) {  
            logger.error("La url no está formada correctamente.");
        } catch (URISyntaxException e) {  
            logger.error("La url no está formada correctamente.");  
        }  

        return u;  

    }
user_14224340

This is what I use to validate CDN urls (must start with https, but that's easy to customise). This will also not allow using IP addresses.

public static final boolean validateURL(String url) {  
    var regex = Pattern.compile("^[https:\\/\\/(www\\.)?a-zA-Z0-9@:%._\\+~#=]{2,256}\\.[a-z]{2,6}\\b([-a-zA-Z0-9@:%_\\+.~#?&//=]*)");
    var matcher = regex.matcher(url);
    return matcher.find();
}
user_44529250
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