Reading values between HTML tags.

[bholzer]

I want to write a program to run continuously in the background that will alert me when a value on a web page has changed.

The value is within a unique tag on the page.

How would I even begin to go about this?

[doWhile]

Lesson: Regular Expressions (The Java™ Tutorials > Essential Classes) will allow you to parse the html and find certain content. That being said, if by change you mean change via a script such as javascript the problem becomes exponentially more complicated.

[bholzer]

Yea, I just want to parse html generated by php content.

[Solarsonic]

Use an URL and a BufferedReader like so:

URL url = new URL("direct url to page");
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

[bholzer]

I've gotten that far, but once I'm there, how do I designate exactly which values to pull?

[Maximus-EVG]

I've gotten that far, but once I'm there, how do I designate exactly which values to pull?

Well the solution is to parse the page line by line, and find what you need based on regular expressions, or simple string operations.
Hehe actually Im writing an article on a multithreaded webcrawler, so what I need are the html pages enclosed in <a href= </a> tags.
Here's how I do it, perhaps you can adapt it to your own design.

public void scrapeYourself() throws IOException{
		InputStream input = theURL.openConnection().getInputStream();
		BufferedReader reader = new BufferedReader(new InputStreamReader(input));		
		String line;
		int startIndex = 0;
		int endIndex = 0;
		
		while ((line = reader.readLine()) != null){
			//System.out.println(line);
			/*See if <aref=.... > tag is present. Stuff (link name, target attribute
			 *  can be in between <aref="" and </a>, but consider simplest case for now  */
			if (line.contains("<a href=\"http:") && line.contains("</a>") && (line.indexOf("<a href=\"http:") < line.indexOf("</a>"))){
				//System.out.println("The line: " + line);
				String[] linkTokensWithinLine = line.split("<a href=\"");
				String theLink = null;		
				/* Method 2  */
				for (int i = 0; i < linkTokensWithinLine.length; i++){
					/*Ignore part of the line before the first <a href=...> split */
					if (linkTokensWithinLine[i].contains("</a>")){
						try{
						theLink = linkTokensWithinLine[i].substring(linkTokensWithinLine[i].indexOf("http:"), linkTokensWithinLine[i].indexOf("\"", linkTokensWithinLine[i].indexOf("http:")+ 7));
						} catch (StringIndexOutOfBoundsException ex){
							//If link is in javascript:/etc... format, just ignore it.
						}
					//System.out.println("" + i + ": " + linkTokensWithinLine[i]);
					//System.out.println("Absolute URL: " + theLink); 
					/*Add the proper URL to the list of this link's sublinks */
					this.allSublinks.add(new Link(new URL(theLink), this.crawler));
					/*Debugging: */
					//System.out.println("    Sublink:" + this.allSublinks);
					}
				/*Method 2 END */

				}				
			}
			
		}
		/*Release the resources */
		reader.close();
		input.close();
	}

[doWhile]

Have you looked at the link I provided above? Did you try using anything learned in it, and if so what? A Pattern/Matcher combo will allow you to parse text in ways unimaginable, and is a powerful tool a programmer should have in their arsenal. You've provided little insight into what tag you wish to grab and what about it you want, so posting an SSCCE or example will help as well.