Getting started on exploring a complex java project

Question

In the project allocated to me I have to understand a big Java project which uses Spring framework and angularjs for the frontend and I don't know where to start with. There is a lot of code running on the server (Jetty) and lots of logs generated. The back-end code is more of an interest for me than the UI side.

My question is where do I start? The Java code that we use for practice in college/academics very simple and had a 'main' method to start with.

In the big project I don't see a main method. How do I find out the 'starting point' of the project and then explore it further?

This question is somewhat similar but not exactly to Understanding a big company project in Java

Answer 1

One possible way to start exploring is find an important entry point to the application and then analysis layer to layer from code to code.

My following explanation is based on the information you have give in the comments of your questions. (application is based on angularjs and spring). It would be a good idea to adjust your question, so that these important informations are a part of the question (comments are temporary and could be removed without notice)

Start the application and find one of it's main functionality (or the functionality you want to extend on the next task).

Open the developer tools of your favourite browser and record all requests and responses. Trigger the action you want to discover. Analysis the records and find the corresponding REST call. Look at the request and response param and think about what this API should do.

Then you search for the corresponding REST-Controller inside the backend code. In most situation you can find it, if you search for some of the latter values of the REST-Call-URL path (which is bind to the controller or a controller method).

Now you have your entry point for that action and you can discover further on more or less similar as you would do it on a main method.

You can repeat this steps to get a understanding of the implementation of some features (one by one). Nevertheless there could be some important part of the application you will not find with this approach. But it would give you a starting point to explore the functions which are exposed by the web-interface to the user.

Depending on the architecture it might be that you find a place with some central core functionality. Then it would be a good idea to explore these core functions independently of the api to the frontend. If the application f.e. would take advance of a domain driven design approach you would find a layer where a functional (not technical) domain is designed. Then you will find the bigger picture here.

If you have anyone who know how the application is designed you should of course start you discovery by interviewing this person. If every one who has knowledge is not reachable, you have to look at some documentation or you have to discover the application on your own like I try to describe.