As mentioned earlier, using annotations is one of the most common ways to configure your entities and relationships with Hibernate. However however, there are some things that can get pretty tedious when doing it repetitively for many objects.

That’s where XML comes into play!

XML is much more readable than plain text or JSON as they're more like documents. You can easily see the structure of the document without having to do any additional work.

This article will go over all of the different types of hibernates mapping files available and how to use each one depending on the needs of your project.

Disclaimer: The content in this article should be viewed with caution if you are not very familiar with both Hibernate and XML. There are some concepts discussed that may feel advanced but aren't too complicated.

Session factory

A session factory is an object that contains various settings for your database, mapping information, and other internal state. Depending on what you want to do with Hibernate, there are usually no hard and fast rules on what kind of setting you need to have.

But most applications require at least one entry in a user table, so having a column for that entry will make sense. Therefore, almost every application requires a table to store users.

Hence, nearly all Java apps using Hibernate will include a User class within their app along with a SessionFactory instance variable. The two work together by the User class being mapped to the database and then the SessionFactory creating objects of the User class when needed.

The reason why this happens is because both pieces of software code can be copied and pasted into any project easily.

Entity manager

An entity management layer is needed to access data from your database. This layer will take care of interacting with your database, creating instances of mapped classes (or entities), and caching these instances for performance benefits.

The most common way to use this layer is via what’s called active fetching. Active fetching means that the entity managers looks up all the objects in the beginning and then caches them until they are used later.

This can be inefficient because it requires too much memory at once or too many round trips to the server to obtain the cached information. With large applications, this can become quite expensive.

Hibernate offers another type of mapping tool which does not require an entity manager. These tools are known as second level cache providers.

What is a second-level cache?

A second level cache is a storage area where frequently accessed data can be stored to reduce the workload on the DBMS and/or the network bandwidth. For example, if you enter a lot of items into a shopping cart programatically, you do not need to rerun those commands every time someone runs out of something!

Second level caches work by keeping a copy of the data around locally. More advanced second level caches even have settings such as how old the data must be to be deleted to make room for more recent content.

Unit of work

The unit of work is an important concept when working with any software that utilizes a database. This concept was first discussed in depth by Martin Fowler in his article Introduction to Units of Work.

A unit of work (or transaction) is a set of changes or operations done within a specific area or context. For example, let’s say you are running a restaurant and need to do some remodeling. You will probably start by taking down some walls and creating new tables.

After this, you will need to wash all the dishes and put away the leftovers. Then, you will have to clean up the kitchen! All of these tasks are considered part of one big project so they are grouped into a unit of work called “remodel the restaurant.

A/B testing

One of the most important things to do as developer is to try new ways to improve your application or even create new applications.

Running an experiment on your own website can be tricky though, which is why there are professionals that offer A/B testing services. These individuals test different versions of a page or feature and see what performs better for your business.

A common way to use A/B testing with web pages is through using either Google’s or Bing’s free tool for creating a new version of a site you already have. This allows you to add more decorations or cut down some content so you can determine which one works best for your audience.

For example, if your site contains educational information about how to bake the perfect chocolate chip cookie, you could test whether adding an extra step makes people less likely to skip over it or not.