It is good practice to verify the integrity of the distribution files.
You are currently using http://psg.mtu.edu/pub/apache/. If you encounter a problem with this mirror, then please select another. If all mirrors are failing, there are backup mirrors at the end of the list. See status of mirrors.
The api project contains source to build jdo-api.jar, which defines the JDO API. The jar file is the only artifact needed for users who wish to compile their programs using the JDO API. It can be downloaded automatically by maven and placed into the local maven repository if you include the proper dependency in your maven project definition. Use groupId javax.jdo, artifactId jdo-api, version 3.1-rc1 and define your remote repository as http://www.ibiblio.org/maven. Alternatively, it can be downloaded manually and put into a location of your choice.
This is a download for all implementors of JDO, and for those who want to check how well an implementation is compliant with the JDO specification. The tck2 project contains the JDO 2 Technology Compatibility Kit. The source distribution is the only artifact needed to be downloaded by the user. The dependencies are automatically downloaded by maven as needed to run the TCK.
It is essential that you verify the integrity of the downloaded files using the PGP signature.
The PGP signatures can be verified using PGP or GPG. First download the KEYS as well as the asc signature file for the particular distribution. Make sure you get these files from the main distribution directory, rather than from a mirror. Then verify the signatures using
% pgpk -a KEYS
% pgpv release_name.tar.gz.asc
% pgp -ka KEYS
% pgp release_name.tar.gz.asc
% gpg --import KEYS
% gpg --verify release_name.tar.gz.asc