Validating URL in Java

Question

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

User · Answer

Use the android webkit URLUtil on android   URLUtil isValidUrl URL STRING     Note  It is just checking the initial scheme of URL  not that the entire URL is valid

User · Answer

There is a way to perform URL validation in strict accordance to standards in Java without resorting to third-party libraries   boolean isValidURL String url      try       new URI url  parseServerAuthority        return true      catch  URISyntaxException e        return false          The constructor of URI checks that url is a valid URI  and the call to parseServerAuthority ensures that it is a URL  absolute or relative  and not a URN

User · Answer

For the benefit of the community  since this thread is top on Google when searching for  url validator java     Catching exceptions is expensive  and should be avoided when possible  If you just want to verify your String is a valid URL  you can use the UrlValidator class from the Apache Commons Validator project   For example   String   schemes     http   https       DEFAULT schemes    http    https    ftp  UrlValidator urlValidator   new UrlValidator schemes   if  urlValidator isValid  ftp   foo bar com          System out println  URL is valid      else      System out println  URL is invalid

User · Answer

You need to create both a URL object and a URLConnection object   The following code will test both the format of the URL and whether a connection can be established   try       URL url   new URL  http   www yoursite com         URLConnection conn   url openConnection        conn connect      catch  MalformedURLException e           the URL is not in a valid form   catch  IOException e           the connection couldn t be established

User · Answer

The java net URL class is in fact not at all a good way of validating URLs  MalformedURLException is not thrown on all malformed URLs during construction  Catching IOException on java net URL openConnection   connect   does not validate URL either  only tell wether or not the connection can be established   Consider this piece of code       try           new URL  http    com            new URL  http   com             new URL  http                new URL  ftp        example com          catch  MalformedURLException malformedURLException            malformedURLException printStackTrace              which does not throw any exceptions   I recommend using some validation API implemented using a context free grammar  or in very simplified validation just use regular expressions  However I need someone to suggest a superior or standard API for this  I only recently started searching for it myself   Note It has been suggested that URL toURI   in combination with handling of the exception java net  URISyntaxException can facilitate validation of URLs  However  this method only catches one of the very simple cases above   The conclusion is that there is no standard java URL parser to validate URLs

User · Answer

Thanks  Opening the URL connection by passing the Proxy as suggested by NickDK works fine     Proxy instance  proxy ip   10 0 0 1 with port 8080 Proxy proxy   new Proxy Proxy Type HTTP  new InetSocketAddress  10 0 0 1   8080    conn   new URL urlString  openConnection proxy     System properties however doesn t work as I had mentioned earlier   Thanks again   Regards  Keya

User · Answer

Using only standard API  pass the string to a URL object then convert it to a URI object  This will accurately determine the validity of the URL according to the RFC2396 standard   Example   public boolean isValidURL String url         try           new URL url  toURI          catch  MalformedURLException   URISyntaxException e            return false             return true

User · Answer

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 est   formada correctamente                               u   new URL url                 u toURI               catch  MalformedURLException e                  logger error  La url no est   formada correctamente               catch  URISyntaxException e                  logger error  La url no est   formada correctamente                            return u

User · Answer

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 · Answer

Are you sure you re using the correct proxy as system properties   Also if you are using 1 5 or 1 6 you could pass a java net Proxy instance to the openConnection   method  This is more elegant imo     Proxy instance  proxy ip   10 0 0 1 with port 8080 Proxy proxy   new Proxy Proxy Type HTTP  new InetSocketAddress  10 0 0 1   8080    conn   new URL urlString  openConnection proxy

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