That's the question: Which library can help me to access data available via WebDAV in my Java-programs? OpenSource is preferred.
Apache's Jakarta Project has a WebDav Construction Kit, which should fit this need.
The now deprecated Apache Jakarta Slide project includes a Java WebDAV client library - but this project is retired due to the lack of a developer community.
Apache Jackrabbit is mentioned as alternative to Slide. You might want to check if its WebDAV library can be used instead.
If you just want to access files from a WebDAV repository, you can simply use a HTTP library as WebDAV builds upon HTTP. You only need a WebDAV client library if you want to use WebDAV features like locking, directory listings or access to properties (meta-data).
http://sourceforge.net/projects/webdavclient4j/ is based on the retired Apache Jakarta Slide project's Java webdav client, and includes the VFS WebDAV provider. It is packaged with HttpClient 3.0.1.
I created a very easy to use java webdav client: http://sardine.googlecode.com/