Regular Expressions in String's split() method.

[Siju Odeyemi]

I've got a String variable expFile with the following value in it:

<p> 'Would you like to come over?' enquired the Rat presently.</p> <p> 'Oh, its all very well to TALK,' said the Mole, rather pettishly, he being new to a river and riverside life and its ways.</p> <p> The Rat said nothing, but stooped and unfastened a rope and hauled on it; then lightly stepped into a little boat which the Mole had not observed. It was painted blue outside and white within, and was just the size for two animals; and the Mole's whole heart went out to it at once, even though he did not yet fully understand its uses.</p> <p> The Rat sculled smartly across and made fast. Then he held up his forepaw as the Mole stepped gingerly down. 'Lean on that!' he said. 'Now then, step lively!' and the Mole to his surprise and rapture found himself actually seated in the stern of a real boat.</p> <p> 'This has been a wonderful day!' said he, as the Rat shoved off and took to the sculls again. 'Do you know, I've never been in a boat before in all my life.'</p> <p> 'What?' cried the Rat, open-mouthed: 'Never been in a--you never-- well I--what have you been doing, then?'</p> <p> 'Is it so nice as all that?' asked the Mole shyly, though he was quite prepared to believe it as he leant back in his seat and surveyed the cushions, the oars, the rowlocks, and all the fascinating fittings, and felt the boat sway lightly under him.</p> <p> 'Nice? It's the ONLY thing,' said the Water Rat solemnly, as he leant forward for his stroke. 'Believe me, my young friend, there is NOTHING--absolute nothing--half so much worth doing as simply messing about in boats. Simply messing,' he went on dreamily: 'messing-- about--in--boats; messing----'</p> <p> 'Look ahead, Rat!' cried the Mole suddenly.</p> <p> It was too late. The boat struck the bank full tilt. The dreamer, the joyous oarsman, lay on his back at the bottom of the boat, his heels in the air.</p> <p> '--about in boats--or WITH boats,' the Rat went on composedly, picking himself up with a pleasant laugh. 'In or out of 'em, it doesn't matter. Nothing seems really to matter, that's the charm of it. Whether you get away, or whether you don't; whether you arrive at your destination or whether you reach somewhere else, or whether you never get anywhere at all, you're always busy, and you never do anything in particular; and when you've done it there's always something else to do, and you can do it if you like, but you'd much better not. Look here! If you've really nothing else on hand this morning, supposing we drop down the river together, and have a long day of it?'</p> <p> The Mole waggled his toes from sheer happiness, spread his chest with a sigh of full contentment, and leaned back blissfully into the soft cushions. 'WHAT a day I'm having!' he said. 'Let us start at once!'</p> <p> 'Hold hard a minute, then!' said the Rat. He looped the painter through a ring in his landing-stage, climbed up into his hole above, and after a short interval reappeared staggering under a fat, wicker luncheon-basket.</p> <p> 'Shove that under your feet,' he observed to the Mole, as he passed it down into the boat. Then he untied the painter and took the sculls again.</p> <p> 'What's inside it?' asked the Mole, wriggling with curiosity.</p>

THEN I split the string using the following method:

String[] splitExpFile = expFile.split("</p>");

I'm trying to write a regular expression to split the file after every 10 paragraphs OR at every 1000 characters at most. Unfortunately, I can't seem to get the regular expression right. Can someone with regex skills please show me the light? I'm quite desperate.

Thanks in advance.

[prem pillai]

have a look at java.util.regex.Matcher ....

[Wouter Oet]

I think that he knows about the Matcher class since he is asking for someone with regex skills. However what have you tried so far? The regex you're looking for isn't very complicated.

[Siju Odeyemi]

prem & Wouter, thanks for responses.

I don't know regexp syntax at all, I know that the split method breaks the string up everytime it encounters the </p> tag, but I need an expression that does what I explained in my opening post.

Cheers guys.

[prem pillai]

but I need an expression that does what I explained in my opening post.

Why are you insisting that it should be done using a regex ? If you are not comfortable with regexes , why don't you have a look at other options to break up your string? There are options available in java.lang.String class itself. Why dont you give it a try ... in the simple way first.

[Henry Wong]

Siju Odeyemi wrote:
I'm trying to write a regular expression to split the file after every 10 paragraphs OR at every 1000 characters at most. Unfortunately, I can't seem to get the regular expression right. Can someone with regex skills please show me the light? I'm quite desperate.

Generally, split() is good when you can describe what you want in terms of it's delimiters. Descriptions like "10 paragraphs" are more towards what you actually want, than how they are separated. In those cases, it is probably better to use the find() method instead of the split() method.

Henry

[Henry Wong]

Siju Odeyemi wrote:I don't know regexp syntax at all, I know that the split method ....

I seriously recommend against using regexes if you don't know how they work (or their syntax). With regex, it is very easy to write code that you don't understand, even with some experience; to try it with no experience at all is sure to wind up with code you don't understand (and completely unmaintainable).

Henry

[Vinoth Kumar Kannan]

Siju Odeyemi wrote:
I don't know regexp syntax at all....

Regex is no big deal. Its easy, yes. A few tutorials and trying out a few sample code would get you going.
I suggest you try reading this - http://www.regular-expressions.info/tutorial.html
This one is really good & easy to understand.

[Campbell Ritchie]

Vinoth Kumar Kannan wrote: . . . Regex is no big deal. Its easy, yes. . . .

. . . and,

I'm from the Government; I'm here to help.
The cheque's in the post.
etc etc

[James Sabre]

Henry Wong wrote:
I seriously recommend against using regexes if you don't know how they work (or their syntax). With regex, it is very easy to write code that you don't understand, even with some experience; to try it with no experience at all is sure to wind up with code you don't understand (and completely unmaintainable).

++

But if you do know how they work then

        String[] splitS = s.split("(?s)(?<=\\G.{1000})|(?<=\\G(?:<p>){10})");

[Joanne Neal]

James Sabre wrote:

        String[] splitS = s.split("(?s)(?<=\\G.{1000})|(?<=\\G(?:<p>){10})");

As Vinoth said. Easy

[James Sabre]

Joanne Neal wrote:

James Sabre wrote:

        String[] splitS = s.split("(?s)(?<=\\G.{1000})|(?<=\\G(?:<p>){10})");

As Vinoth said. Easy

Certainly not difficult and I would normally write it with comments to make it obvious; something along the lines

      String[] splitS = s.split(
                "(?s)" // set DOT ALL option (allow '.' to match any char including new line)
                + "(?<=\\G.{1000})" // look behind and split if there have been 100 characters since the previous split
                + "|" // OR
                + "(?<=\\G(?:<p>){10})" // look behind and split if there have been 10 '<p>' since the previous split
                );
 

Regex don't have to be difficult and the biggest problem I see with regex is people trying to write them as one long string. Yes, one can write very very complex regex that are incomprehensible probably even to the author but the same applies to any computer language; it just happens to be easier to do with regex.

If you want to see really incomprehensible syntax then take a look at APL. I spent several years teaching APL and learned to both love and hate the mathematical notation.

Edit : :-( Must be complex regex since nobody has pointed out that my regex is actually rubbish so I have added weight to the arguments of those who are against regex. At this time I can't correct the regex. Funny really since my initial approach would have been to use Pattern with Matcher.find() and that is easy to code correctly. Using StringTokenizer would follow the same approach as Pattern and Matcher.find() so would probably be easier still.

[Harivittal Atreya Hk]

Why Dont you try solving it with "StringTokenizer class", you can specify the common occurences at the end of 1000 chars as its a static doc.

[Henry Wong]

James Sabre wrote:Edit : :-( Must be complex regex since nobody has pointed out that my regex is actually rubbish so I have added weight to the arguments of those who are against regex. At this time I can't correct the regex.

That's the other thing about regexes, a complex regex is just a mess of characters....

I won't try to fix this, but if you want to, I would first recommend adding the matches for the characters, in-between the paragraph markers. The way it is written, it will only match if the markers are back to back.

Second, you will likely run into the issue that unbounded regexes are not allowed for look-behinds. To fix that, you can't use "*", or "+", which isn't a problem; it isn't a problem because the maximum match is a 1000 characters anyway. You can cap each at 1000 characters, which will bound the look behind as no more than 10,000 characters, which will trigger the other part of the pattern anyway.

Third, there may be some issues with the start and end boundaries.

And at this point, I am sure that I missed something...

Henry