Java – Get source of website in java

javaurl

I would like to use java to get the source of a website (secure) and then parse that website for links that are in it. I have found how to connect to that url, but then how can i easily get just the source, preferraby as the DOM Document oso that I could easily get the info I want.

Or is there a better way to connect to https site, get the source (which I neet to do to get a table of data…its pretty simple) then those links are files i am going to download.

I wish it was FTP but these are files stored on my tivo (i want to programmatically download them to my computer(

Best Answer

You can get low level and just request it with a socket. In java it looks like

// Arg[0] = Hostname
// Arg[1] = File like index.html
public static void main(String[] args) throws Exception {
    SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault();

    SSLSocket sslsock = (SSLSocket) factory.createSocket(args[0], 443);

    SSLSession session = sslsock.getSession();
    X509Certificate cert;
    try {
        cert = (X509Certificate) session.getPeerCertificates()[0];
    } catch (SSLPeerUnverifiedException e) {
        System.err.println(session.getPeerHost() + " did not present a valid cert.");
        return;
    }

    // Now use the secure socket just like a regular socket to read pages.
    PrintWriter out = new PrintWriter(sslsock.getOutputStream());
    out.write("GET " + args[1] + " HTTP/1.0\r\n\r\n");
    out.flush();

    BufferedReader in = new BufferedReader(new InputStreamReader(sslsock.getInputStream()));
    String line;
    String regExp = ".*<a href=\"(.*)\">.*";
    Pattern p = Pattern.compile( regExp, Pattern.CASE_INSENSITIVE );

    while ((line = in.readLine()) != null) {
        // Using Oscar's RegEx.
        Matcher m = p.matcher( line );  
        if( m.matches() ) {
            System.out.println( m.group(1) );
        }
    }

    sslsock.close();
}

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Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

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Java is always pass-by-value. Unfortunately, when we deal with objects we are really dealing with object-handles called references which are passed-by-value as well. This terminology and semantics easily confuse many beginners.

It goes like this:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

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In the example above aDog.getName() will still return "Max". The value aDog within main is not changed in the function foo with the Dog "Fifi" as the object reference is passed by value. If it were passed by reference, then the aDog.getName() in main would return "Fifi" after the call to foo.

Likewise:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
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In the above example, Fifi is the dog's name after call to foo(aDog) because the object's name was set inside of foo(...). Any operations that foo performs on d are such that, for all practical purposes, they are performed on aDog, but it is not possible to change the value of the variable aDog itself.

For more information on pass by reference and pass by value, consult the following SO answer: https://stackoverflow.com/a/430958/6005228. This explains more thoroughly the semantics and history behind the two and also explains why Java and many other modern languages appear to do both in certain cases.

Best Answer

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