It was perhaps not clear in my first mail, but in Jetty, HTTP-Post perfectly works, it does not work with Tomcat however. So the question is: Has Jetty a bug (that it works but it shouldn't) or has Tomcat a bug (that it conforms to some standard so that it is not allowed to work)? And has anyone a workaround I can use now so that Solrj & HTTP-Post works with Tomcat?
I would first try setting the charset in the POST explicitly to UTF-8. This shouldn't matter, but it appears that Resin & Tomcat both have had issues with not properly handling form data without this.
It shouldn't matter, but there's also the issue of configuring Tomcat to handle UTF-8 encoded URLs - http://wiki.apache.org/solr/SolrTomcat
Also see https://issues.apache.org/jira/browse/SOLR-214, where there was a patch applied on May 7th of this year to work around what appears to be a bug with Tomcat. I assume you have a version of Solr with this patch.
-- Ken -- Ken Krugler Krugle, Inc. +1 530-210-6378 "If you can't find it, you can't fix it"