How to integrate ReactJs into legacy JSF Web application?

I have a legacy system that uses JSF technology, and I want to migrate this system to React. JSF uses PrimeFaces UI Component Library, and I am planning to use PrimeReact to make migration easier. However, this system has a lot of pages, so I cannot migrate all the pages at once, and it will take a lot of time. As a result, I want to break the system down into parts and migrate each part one by one. Is there a way to use both JSF and react at the same time? For example, one part of the website works with React, and the other part of the system works with JSF. To be more specific, 60 pages work with React, and 100 pages work with JSF. How can I configure something like that? What will happen to the security of the system? This technology has a login system, so will there be any vulnerabilities? Will this affect the performance of the system? I could not find any detailed information on the internet, so I will be very grateful, if anyone can share their experience about this topic. Thank you in advance.

Amusing that you should refer to JSF as "legacy". It's still very much a part of the JEE standard, even if not much loved. That actually gives it a permanence that React cannot boast any more than Ruby-on-Rails could.

JSF is not greedy. You can not only mix JSF pages with React pages, you can mix them with raw servlets, JSPs, Struts, and in fact any equally non-greedy web framework. The only difference is that if your URL resolves to a non-JSF resource, it won't go through the FacesServlet and won't get any of the Faces-specific benefits.

Now personally, I can't think of anything that React can give that PrimeFaces cannot when it comes to responsive UIs, but of course if you have a bunch of JReact-heads on your team and no significant JSF talent, you might feel obliged to accommodate them. and as I said, no problem. Just remember to pass your stuff in session-scope beans or higher.

Murat Savas wrote: What will happen to the security of the system? This technology has a login system, so will there be any vulnerabilities?

It depends. If it's a privately-designed login system, I can virtually assure that there will be vulnerabilities. And always were. If you have been using a professionally-designed and-vetted login system like the one JEE builds into every webapp server, most likely not.

Incidentally, I AM assuming that React, JSF, or whatever, everything's talking to a common Java backend webapp. If your React backend isn't Java, then you'll definitely have to co-ordinate security, as well as any data passing (since JEE session objects aren't accessible from outside the JVM). In other words, you'll be running multiple webapps, even if they present to the user as a single app, and you'll have to design accordingly.