Well, I've read many things on the Web and tried to collected as many information as possible. This is how I could find the solution:
here is my solrconfig.xml:
...
<!-- ****** Data import handler -->
<requestHandler name="/dataimport" class="org.apache.solr.handler.dataimport.DataImportHandler">
<lst name="defaults">
<str name="config">data-config.xml</str>
</lst>
</requestHandler>
...
<lib dir="../../../dist/" regex="solr-dataimporthandler-.*\.jar" />
Here is my data-config.xml: (important: it must be in the same folder of solrconfig.xml)
<dataConfig>
<dataSource type="FileDataSource" encoding="UTF-8" />
<document>
<entity name="page"
processor="XPathEntityProcessor"
stream="true"
forEach="/mediawiki/page/"
url="/Applications/solr-4.6.0/example/exampledocs/simplewikiSubSet.xml"
transformer="RegexTransformer,DateFormatTransformer"
>
<field column="id" xpath="/mediawiki/page/id" />
<field column="title" xpath="/mediawiki/page/title" />
<field column="revision" xpath="/mediawiki/page/revision/id" />
<field column="user" xpath="/mediawiki/page/revision/contributor/username" />
<field column="userId" xpath="/mediawiki/page/revision/contributor/id" />
<field column="text" xpath="/mediawiki/page/revision/text" />
<field column="timestamp" xpath="/mediawiki/page/revision/timestamp" dateTimeFormat="yyyy-MM-dd'T'hh:mm:ss'Z'" />
<field column="$skipDoc" regex="^#REDIRECT .*" replaceWith="true" sourceColName="text"/>
</entity>
</document>
</dataConfig>
Attention: The last line is very important!
My schema.xml:
...
<field name="id" type="string" indexed="true" stored="true" required="true"/>
<field name="title" type="string" indexed="true" stored="false"/>
<field name="revision" type="int" indexed="true" stored="true"/>
<field name="user" type="string" indexed="true" stored="true"/>
<field name="userId" type="int" indexed="true" stored="true"/>
<field name="text" type="text_en" indexed="true" stored="false"/>
<field name="timestamp" type="date" indexed="true" stored="true"/>
<field name="titleText" type="text_en" indexed="true" stored="true"/>
...
<uniqueKey>id</uniqueKey>
...
<copyField source="title" dest="titleText"/>
...
And it's done. That's all folks!