Java – add “http: / /” before my address

I extract addresses from a source, but some extracts do not have http: / / addresses in front of them. How can I check whether the addresses have http: / / if they are not, how can I add http: / / infrant?: o

I guess this error is due to the "lack" of http: / / infrant

java.net.MalformedURLException: no protocol: www.speedtest.net
at java.net.URL.<init>(URL.java:583)
at java.net.URL.<init>(URL.java:480)
at java.net.URL.<init>(URL.java:429)
at a.PageRead.r(PageRead.java:29)
at a.ThreadDownloaderWriter.run(ThreadDownloaderWriter.java:35)
at java.lang.Thread.run(Thread.java:722)






 public StringBuilder readPage() {
        try {

            URL url = new URL(this.strURL);
            System.out.println(this.strURL);
            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
            String line;
            StringBuilder sb = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            reader.close();

            return sb;
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return new StringBuilder("");
        } catch (IOException e) {
            e.printStackTrace();
            return new StringBuilder("");
        }
    }

Solution

The literal answer to your question is as follows:

String url = ... ; // Whatever
if (!url.startsWith("http://")) {
    url = "http://" + url;
}

But this is still not a good solution For example, how about HTTPS URLs? How about FTP or even file system URL (file: / /) Then you may want to consider case sensitive things ("http: / /"! = "http: / /"! = "http: / /" even if they actually mean the same thing and will be accepted through the Java URL class)

You can try to be more careful:

if (!url.toLowerCase().matches("^\\w+://.*")) {
    url = "http://" + url;
}

This matches the beginning of the URL string with any "word character" followed by a colon (:) and two slashes (/ /), and then defaults to http: / / if the protocol part of the URL is missing This will cover more cases than the original (text) answer

Finally, if someone gives you a URL without a protocol part, it is an invalid URL

You should consider reading a book on Java programming because these are basic logic / Java API issues