Ok, several things upfront:
** You WILL have to learn precisely how regex works in
java. Here is a good tutorial link
regex torial from Sun.
** Note there are some subtle differences between regular expressions in different languages. So, no universal standard.
** Pay particular attention to when
you should use Greedy, Reluctant and Possessive quantifiers. It's critically important - means difference
between a working regular expressions and a regular expressions which looks like it SHOULD work, yet it DOESN't -
the most likely reason is in how you use the quantifiers. So learn about them in detail.
** You will need a
test harness to try out your regular expressions in an easy way - the tutorial luckly has one for you to download.
It's a good one.
Ok, here are some ideas about how i did it which can help you get started once you learn enough about how regex works in java:
(NOTE: if you don't understand something,don't get stuck, just keep reading - i try to reiterate some important points, so you'll
see me talk about them again)
criteriaFind(
String criteria) {
//PHASE NUMBER 1 (better to put it in a separate //function: String [] func1(String criteria)):
//separate the criteria into its constituent //elements with "any character" regex prepended //and postfixed to them;
//for example: "criteria=Origin //airport='ABC',Destination airport='DFG'" yeilds //an array of strings:
//.*?Origin airport='ABC'.*?
//.*?Destination airport='DFG'.*?
//To get this result, you need to come up with a //regex which matches a correct criteria input //string. If the criteria is wrong, your
//regex (if constructed properly) will NOT match //it. Note, you will need to use the group() //function after that
//in the Matcher class to obtain all the //key='value' pairs. As soon as you get a pair, //prepend it and postfix it with .*? - a "any //number
//of any characters" match (we will see why we //need it later). So eventually, you will be able //to get all of these .*?fieldname='value'.*?
//(or .*?key='value'.*? as i called it before) //and store it in an array of strings. Then //func1() returns all of them in a String[].
//Basically func1() is using regex (designed by //you) to construct a bunch or regex's (those //stored in a String[] returned by func1())
//we will use to do more matching later.
//ok, let's review func1() in brief one more time //(i understand, it's very tricky):
//
// 1) Create a regex which represents a correct //input for criteria.
// 2) Try to match your criteria against this //regex. If it doesn't match, return new //String[0];
// This is the most heavyweight regex in this //whole deal. Carefully think it through (hint: //think of the most general correct value
// for your criteria).
// 3) Ok, now the criteria is correct (no weird characters, or wrong format). So use another regex //(a much much smaller one) to pick out
// all the fieldname='value' pairs, prepend //and postfix each one of them with .*? and put it //in the next available String slot in your
// String[]. This procedure will use the //group() method in the Matcher class.
//
//do the actual record matching here
synchronized (this) { //to make sure noone //attempts to change the reccount by adding or //deleting records.
for (every record in the database) {
//PHASE NUMBER 2: (String func2(DataInfo rec))
/*puts rec into key1='value1'key2='value2'key3='value3' ..... format and returns it as one large String (let's call it str)*/
for (every one of those .*?key='value'.*? pairs we obtained above) {[
/*match it with str. If match is not found break out of this loop to go to the next record. */
/*If all the
patterns matched a given record, that means all the key='value' pairs in the original criteria were present in this record, so grab this record and put it in some storage (a Vector, maybe) */
}
}
/*create DataInfo[] out of that storage (the one containing all the matched records) and return it. */
}
}
hope this helps
-lev
