Solr and custom update handler

I have a question about Solr and the possibility to implement a customized update handler

Basically, the scenario is this:

• FIELD-A : my main field
• FIELD-B and FIELD-C : 2 copyfield with source in A

After FIELD-A has its value stored, i need this valued to be copied in FIELD-B and C, then processed (let's say extract a substring) and stored in FIELD-B and C before indexing time. I'm not using DIH.

edit: i'm pushing my data via nutch (forgot to men开发者_Go百科tion that)

As far as i've understood, copyfields triggers after indexing (but i'm not so sure about this).

I've already read throu the wiki page and still i don't understand a lot of things:

1) customupdateprocessor is an alternative to conditionalcopyfield or do they have to exist both in my solr?

2) after creating my conditionalcopyfield jar file, how do i declare it in my schema?

3) how do i have to modify my solrconfig.xml to use my updater?

4) if i'm choosing the wrong way, any suggestion is appreciated, better if some examples or well documented links are provided

I read a lot (googling and lucene ml on nabble) but there's not so much documentation about this. I just need to create a custom updater for my two copyfields,

Thanks all in advance!

Its not really complicated.. Following is an excellent link I came across to write a custom solr update handler.

  http://knackforge.com/blog/selvam/integrating-solr-and-mahout-classifier

I tested it in my solr and it just works fine!

If you are using SOLR 4 or planning to use it, http://wiki.apache.org/solr/ScriptUpdateProcessor could be an easier solution. Have fun!