Learning Processing: A Beginner's Guide to Programming Images ...

336 Learning Processing
When you send a URL path into loadStrings( ) , you get back the raw HTML ( “ Hypertext Markup
Language ” ) source of the requested web page. It is the same stuff that appears upon selecting “ View
Source ” from a browser’s menu options. You do not need to be an HTML expert to follow this section,
but if you are not familiar at all with HTML, you might read http://en.wikipedia.org/wiki/HTML .
Unlike with the comma-delimited data from a text fi le that was specially formatted for use in a Processing
sketch, it is not practical to have the resulting raw HTML stored in an array of Strings (each element
representing one line from the source). Converting the array into one long String can make things a bit
simpler. As we saw earlier in the chapter, this can be achieved using join( ) .
String onelongstring = join(lines, " " );
When pulling raw HTML from a web page, it is likely you do not want all of the source, but just a small
piece of it. Perhaps you are looking for weather information, a stock quote, or a news headline. We can
take advantage of the String manipulation functions we learned— indexOf( ) , substring( ) , and length( ) —
to fi nd pieces of data within a large block of text. We saw an early example of this in Exercise 18-2 . Take,
for example, the following String:
String stuff = " Number of apples:62. Boy, do I like apples or what! " ;
Let’s say we want to pull out the number of apples from the above text. Our algorithm would be as
follows:
1.
2.
3.
4.
Find the end of the substring “ apples: ”. Call it start.
Find the fi rst period after “ apples: ” . Call it end.
Make a substring of the characters between start and end.
Convert the String to a number (if we want to use it as such).
In code, this look’s like:
int start = stuff.indexOf( " apples: " ) + 8; // STEP 1
int end = stuff.indexOf( " . " ,start); // STEP 2
String apples = stuff.Substring(start,end); // STEP 3
int apple_no = int(apples); // STEP 4
Th e above code will do the trick, but we should be a bit more careful to make sure we do not run into
any errors if we do not fi nd the substrings . We can add some error checking and generalize the code into a
function:
// A function that returns a substring between two substrings
String giveMeTextBetween(String s, String startTag, String endTag) {
String found = " " ;
// Find the index of the beginning tag
int startIndex = s.indexOf(startTag);
// If we don’t find anything
if (startIndex = = –1) return " " ;
// Move to the end of the beginning tag
startIndex + = startTag.length();
A function to return a String found
between two Strings. If beginning
or end “tag” is not found, the
function returns an empty String.
The “end” of a String
can be found by
searching for the index
of that String and
adding the length to that
index (in this case 8).