Liferay, Inc. hosts its community edition source code at the SourceForge site (http://sourceforge.net/projects/lportal/).
It also hosts its latest version of source code at its own site at http://www.liferay.com/downloads/liferay-portal/available-releases.
Now, paste the previously-mentioned URL in your browser address box, click on the Enter key, and take a look at those packages.
Every release of Liferay Portal comes with the source code. You can compile and build the portal from the source code, if you choose to do so. You can study the source code to learn how Spring and Hibernate are used. You can modify the source code and re-build the portal if you like.
Note
Please note that Liferay Portal is also bundled in popular open source servlet containers or application servers in every release. It is easier to directly install with these bundles.
These are only some of the advantages of using an open source portal product.