More info in this thread:
In DSpace 4.0, we upgraded to Apache Solr 4.4.0 (see
DS-1623) which also has this issue.
As of now, Restlet is still not available in Maven Central. However, they seem to have plans to release to Maven Central in the near future:
Currently, this is not a major issues, but this transitive dependency on http://maven.restlet.org can cause "random" dspace-solr build errors to occur if that third-party maven repository is not available or non-responsive at the time of building DSpace. This 'dspace-solr' build error looks like:
[ERROR] Failed to execute goal on project dspace-solr: Could not resolve dependencies for project org.dspace:dspace-solr:war:5.0-SNAPSHOT: Failed to collect dependencies at org.apache.solr:solr-core:jar:4.4.0 -> org.restlet.jee:org.restlet:jar:2.1.1: Failed to read artifact descriptor for org.restlet.jee:org.restlet:jar:2.1.1: Could not transfer artifact org.restlet.jee:org.restlet:pom:2.1.1 from/to maven-restlet (http://maven.restlet.org): Connection to http://maven.restlet.org refused: Connection refused -> [Help 1]
This ticket is just noting that we have a known issue with a transitive dependency in Solr 4.4.0. Hopefully it gets resolved by Restlet and Solr very soon, and we can upgrade our Solr dependencies as well. For the time being, if you encounter the above error, try to build DSpace again.