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How to verify that URL is valid in Java 1.6?

Answer 1

+1 A:

If I run your code with the type of malformed URI in the bug report then it throws URISyntaxException. So the suggested fix fixes the reported error.

$ java -cp bin UriTest http:\\\\www.google.com\\
java.lang.IllegalArgumentException
    at java.net.URI.create(URI.java:842)
    at UriTest.main(UriTest.java:8)
Caused by: java.net.URISyntaxException: Illegal character in opaque part at index 5: http:\\www.google.com\
    at java.net.URI$Parser.fail(URI.java:2809)
    at java.net.URI$Parser.checkChars(URI.java:2982)
    at java.net.URI$Parser.parse(URI.java:3019)
    at java.net.URI.(URI.java:578)
    at java.net.URI.create(URI.java:840)

Your type of malformed URI is different, and does not appear to be a syntax error.

Instead, catch the null pointer exception and recover with a suitable message.

You could try and be friendly and check whether the URI starts with a single slash "http:/" and suggest that to the user, or you can check whether the hostname of the URL is non-empty:

import java.net.*;

public class UriTest
{
    public static void main ( String[] args )
    {
        try {
            URI uri = URI.create ( args[0] );

            // avoid null pointer exception
            if ( uri.getHost() == null )
                throw new MalformedURLException ( "no hostname" );

            URL url = uri.toURL();
            URLConnection s = url.openConnection();

            s.getInputStream();
        } catch ( Throwable e ) {
            e.printStackTrace();
        }
    }
}

Pete Kirkham 2010-06-29 08:34:11

I do not want to check every possible problem with URL manually, since my understanding is this is exactly what URL/URI should do for me (if I am wrong here this can be a hint what I should do). Catching runtime exception here is an ugly hack I consider to apply if everything else fails, but in general the idea is bad - it can hide other fatal errors happening during the connection. I believe better solution should exist.

Bartłomiej Kalinowski 2010-06-29 09:07:53

@Bartłomiej Kalinowski URI *is* doing the check for you - if the host name is null (URI.getHost()==null when URL.getHost().equals("")) then it throws a NPE to signify that you are connection to a null host. NPE can possibly hide other errors, but then what were you hoping to do in those cases? Whatever the error is, you probably need to ask the user to correct/retry/abort, so the distinction isn't massively important - possibly the difference between IO exceptions and other exceptions matters - you could retry automatically on IO error but not on the others.

Pete Kirkham 2010-06-29 09:34:39

I need to detect that URL is wrong, and tell apart this problem from all other problems like I/O errors etc. The app does not interact with user, so I cannot ask user to retry/correct, and I can expect that URL is wrong (even if it was validated before).

Bartłomiej Kalinowski 2010-06-29 09:38:06

Answer 2

+1 A:

You can use appache Validator Commons ..

UrlValidator urlValidator = new UrlValidator();

urlValidator.isValid("http://google.com");

http://commons.apache.org/validator/

http://commons.apache.org/validator/api-1.3.1/

Shekhar 2010-06-29 08:36:24

I will check that one. My feeling is: if using external validator is the only way to use java.net.URL/URI properly, then I would say that behavior I described is a bug that makes those classes kind of unusable - this would be really strange for a standard class. Maybe I just do not know some important detail/usage precondition?

Bartłomiej Kalinowski 2010-06-29 09:15:32

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