SolrJ's httpclient and httpcore dependency versions should not be synchronized - instead, the httpcore version to use should be drawn from the httpclient POM

The httpcomponents project, which hosts both the httpclient and the httpcore modules, uses Maven as its build system, so when the httpclient POM declares a dependency, it's authoritative (since that's how httpclient is built and tested).

httpclient's httpcore dependency version doesn't always match the httpclient version. Recent examples (look for <httpcore.version> under <properties>) (these are POMs for httpcomponents-client, which is the parent module for httpclient, and declares its submodules' dependencies' versions):

https://svn.apache.org/repos/asf/httpcomponents/httpclient/tags/4.2.3/pom.xml
http://svn.apache.org/repos/asf/httpcomponents/httpclient/tags/4.1.3/pom.xml
http://svn.apache.org/repos/asf/httpcomponents/httpclient/tags/4.1.1/pom.xml

I'm fairly certain that these versions-out-of-sync incidents are not mistakes - I read this email exchange as describing intentionally versioning httpclient separately from httpcore: http://markmail.org/thread/ippp4gbxwwnt6aws.

SolrJ should separately version its httpclient and httpcore dependencies, and should draw the httpcore version from the httpcomponents-client POM.