Using a regular expression to replace everything between tags contained within XML output - regex

Question

I've been trawling the internet trying to find a solution to this issue. Basically I am using a web service provided by the company that runs our support software to retrieve customer tickets and output them (dependent on filtering) through our system so that customers can see from their dashboard which current support tickets they have active. I've managed to get the desired tags from the XML that is returned via the web service and place their content in a html table (therefore listing the active tickets row by row in the table) however, as the ticket description tag is populated with the content from emails sent by clients, there is lots of nasty redundant css and styling that has been applied to the Email that I would like to remove.
So far I have managed to use the 'replace' function to replace some of the redundant content from this email content ->
l_html_build := replace(l_html_build,'<','<');
l_html_build := replace(l_html_build,'>','>');
l_html_build := replace(l_html_build,'&lt;','');
l_html_build := replace(l_html_build,'&gt;','');
l_html_build := replace(l_html_build,'&nbsp;',' ');
However I now need to overwrite the p tags which have all sorts of garbage added to them so that they just become standard p tags->
From this:
<p 0in;"="" 3.0pt="" padding:="" 1.0pt;="" solid="" border-top:="" none;="" _mce_style=""border:" 0in"="" 0in="" 1.0pt;padding:3.0pt="" #b5c4df="" style=""border:none;border-top:solid">
To this:
<p>
I've looked into using the regEXP function listed here psoug however this appears to require a select statement that is performed each time. The data I need to manipulate is stored in a CLOB called l_html_build so is there any way of adapting the regEXP function to be used in a similar way to the replace function above or is there an alternative method that I am not aware of?
I apologise if this is a noob question. My expertise lies in front end development, PHP and MySQL but unfortunately I'm now required to bits of PL/SQL in my new role.
Any help would be greatly appreciated.

Answer 1

Knowing that:
There is no standard PL/SQL package that parses HTML.
You can't reliably parse HTML with regex. Furthermore, Oracle only support basic regular expressions, restricting its capabilities.
You want to stay in PL/SQL
You are left with few options (that I can think of):
Write a simple procedure yourself that will work in most of the cases (but there will be many exceptions that will break your parser).
Use a java parser, load class in database, call java from PL/SQL. Oracle comes with its integrated jvm, so this involves no extra setup.
I would go with option (2) if you want reliability, or option (1) if infrequent but inevitable losses are acceptable.
Since your content will be coming from email client, we can assume that only a tiny (negligible?) fraction will have very obscure HTML.
In that case you could start with simple regex expressions that may need some tweaking:
SQL> SELECT regexp_replace(
2 '<p1 3.0pt="" padding:="" #b5c4df="">
3 text
4 </p>',
5 '<([[:alpha:]]+)[^>]*>',
6 '<\1>') remove_attr_simple
7 FROM dual;
REMOVE_ATTR_SIMPLE
------------------
<p>
text
</p>
This will fail to catch tricky valid HTML (such as <P attr=">">) but since your input is somewhat standard this should be fine often enough. You may need to remove HTML comments with another procedure -- I'm not sure it can be done with regex.

Answer 2

SQL is really not the best tool for this job. Nor will regexes be able to perform this kind of task reliably. You would be better off extracting the data and processing it in another language using an XML parser.
Presumably Oracle itself is not sending these emails. What program does the sending, and can you add some programmatic processing at that point?
Since you already know PHP, here is a discussion of parsing HTML/XML in PHP. Similar tools are available in most other languages.