Converting string to URI

Question

How do i convert String www.mywebsite.com/firefox.txt to URL ? I wanted to use this in the file object and then into the FileReader constructor.

Answer 1

You can use the new URI(string) constructor (for an URI) and the new URL(string) constructor for a URL.

But that won't work with a FileReader - it requires the URI scheme to be file:

If you want to read a remote file, you need something like:

Reader reader = new InputStreamReader(new URL(urlString).openStream(), encoding);

The encoding can be taken from HttpURLConnection obtained by url.openConnection(), but you can also set it to something specific if you know it in advance. (Btw, In the above example I've omitted all I/O resource management)

Note (thanks to @StephenC): the url string must be a valid URL, which means it must start with http://

Answer 2

If your goal is to turn that string is to turn that string (and similar ones) into syntactically valid URLs ... like a typical browser's URL bar does ... then the answer is "use heuristics".

Specifically, you will need to figure out what heuristics are most likely to turn the user's input into the URL that the user meant. Then write some code to implement them. I'd start by doing some experiments with a browser whose behavior you like and try to figure out what it is doing.

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Your comment is unclear, but I think you are saying that the string is a local file name and you want to turn it into "file:" URL.

File file = new File("www.mywebsite.com/firefox.txt");
URL url = file.toURI().toURL();

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If you want to write to a remote file, you can't do that simply using URL object and openStream(). Writing to remote resources identified by URLs typically requires an http or ftp URL, and use of libraries that implement the respective protocol stack.

Similarly, you can't do it withe the FileWriter API ... unless the file lives in a file system that has been mounted; e.g. as an Windows network share. The FileWriter API only works for files in the unified "file system" that the local operating system makes available to your application.

Finally, we get back to the fact that you need to use a valid URL ... not just the syntactically invalid nonsense that most users type into a browser's URL bar.

Answer 3

If you mean that you need to convert That string to a URL string, you can use the URLEncoder class to decode/encode Strings in Url format.

for example:

String encodedurlStr = URLEncoder.encode(url.toString(),"UTF-8"); 

if you need to get a URL Type, the answer below is correct (using the URL class constructor)

Answer 4

new URL("--your url here--") should turn it into a URL, however the File constructor takes a uri not a url so...

try {
    URL url = new URL("--your url here--");
    File f = new File( url.toURI() );
    FileReader reader = new FileReader(f);
} catch (MalformedURL...IOException e.t.c.) { }

However to get the contents of the url you might want to try

new URL("--your url here--").openStream();

and maybe wrap this in an InputStreamReader ala;

new InputStreamReader( new URL("--your url here--").openStream() );

Not tried any of this but see no reason it won't work :)

It may surprise the unintelligent among you that --your url here-- means you to fill in your own url.

Answer 5

If you want to read the contents of a URL like http://www.mywebsite.com/firefox.txt, FileReader won't help you even if you mangle a URL (or rather URI) into a java.io.File somehow.

Using URL.openStream() and an InputStreamReader will get you the string contents of an URL, but might mess up the content because you might ignore the content encoding sent by the server.

I suggest Apache HttpClient and something liek this:

String url = "http://www.mywebsite.com/firefox.txt";

HttpClient client = new DefaultHttpClient();
HttpResponse response = client.execute(new HttpGet(url));
String contents = EntityUtils.toString(response.getEntity());

For a plain text file, this should give you the contents without any encoding issues. (HTML files can specifiy their encoding using meta tags, that can't be handled 100% using an HTTP client)