How to check for a valid URL in Java

Question

What is the best way to check if a URL is valid in Java     If tried to call new URL urlString  and catch a MalformedURLException  but it seems to be happy with anything that begins with http      I m not concerned about establishing a connection  just validity   Is there a method for this   An annotation in Hibernate Validator   Should I use a regex   Edit   Some examples of accepted URLs are http       and http   my favorite site

User · Accepted Answer

Consider using the Apache Commons UrlValidator class

UrlValidator urlValidator = new UrlValidator();
urlValidator.isValid("http://my favorite site!");

There are several properties that you can set to control how this class behaves, by default http, https, and ftp are accepted.

User · Answer

I didn t like any of the implementations  because they use a Regex which is an expensive operation  or a library which is an overkill if you only need one method   so I ended up using the java net URI class with some extra checks  and limiting the protocols to  http  https  file  ftp  mailto  news  urn   And yes  catching exceptions can be an expensive operation  but probably not as bad as Regular Expressions   final static Set lt String gt  protocols  protocolsWithHost   static     protocolsWithHost   new HashSet lt String gt          Arrays asList  new String     file    ftp    http    https              protocols   new HashSet lt String gt          Arrays asList  new String     mailto    news    urn              protocols addAll protocolsWithHost      public static boolean isURI String str      int colon   str indexOf         if  colon  lt  3                       return false     String proto   str substring 0  colon  toLowerCase      if   protocols contains proto       return false     try       URI uri   new URI str       if  protocolsWithHost contains proto           if  uri getHost      null       return false         String path   uri getPath          if  path    null            for  int i path length  -1  i  gt   0  i--              if     lt  gt        indexOf  path charAt i     gt  -1              return false                               return true      catch   Exception ex         return false

User · Answer

The most  foolproof  way is to check for the availability of URL   public boolean isURL String url      try         new java net URL url   openStream   close         return true      catch  Exception ex        return false

User · Answer

Here is way I tried and found useful   URL u   new URL name      this would check for the protocol u toURI       does the extra checking required for validation of URI

User · Answer

Judging by the source code for URI  the  public URL URL context  String spec  URLStreamHandler handler    constructor does more validation than the other constructors  You might try that one  but YMMV

User · Answer

I d love to post this as a comment to Tendayi Mawushe s answer  but I m afraid there is not enough space     This is the relevant part from the Apache Commons UrlValidator source          This expression derived taken from the BNF for URI  RFC2396       private static final String URL PATTERN                                                                                      12            3  4          5       6   7        8 9         Schema Protocol  ie  http   ftp   file   etc       private static final int PARSE URL SCHEME   2          Includes hostname ip and port number      private static final int PARSE URL AUTHORITY   4   private static final int PARSE URL PATH   5   private static final int PARSE URL QUERY   7   private static final int PARSE URL FRAGMENT   9    You can easily build your own validator from there

User · Answer

validator package   There seems to be a nice package by Yonatan Matalon called UrlUtil  Quoting its API   isValidWebPageAddress java lang String address  boolean validateSyntax                         boolean validateExistance   Checks if the given address is a valid web page address    Sun s approach - check the network address  Sun s Java site offers connect attempt as a solution for validating URLs   Other regex code snippets   There are regex validation attempts at Oracle s site and weberdev com

User · Answer

My favorite approach  without external libraries   try       URI uri   new URI name           perform checks for scheme  authority  host  etc   based on your requirements      if   mailto  equals uri getScheme       Code        if  uri getHost      null     Code       catch  URISyntaxException e

[java] How to check for a valid URL in Java?

Examples related to java

Examples related to validation

Examples related to url