How can I use Java in React application with MySQL for the database. Any suggestion?

https://github.com/callicoder/spring-security-react-ant-design-polls-app

This example will give you a headstart.

I recommend you setup the API ( JAVA and MYSQL ) https://www.javahelps.com/2017/11/restful-crud-with-java-and-mysql-in.html

And then look for other tutorials how to connect to REST API with REACT. Ex below https://www.andreasreiterer.at/connect-react-app-rest-api/

You can use Java as a backend in which you can use spring boot for creating a microservices which act as a restful API for your frontend in react JS. Use axios to call the rest API from your react app to spring boot api. Java is very handy with number of data bases you can use their jars to add connections and you can perform crud operation in Java. It could be anything at the backend but it should be a rest API. Logic related to authentication can be implemented in Java and the routing should be done at the front end in react JS because here we are not using node JS, if you wish you can add the node JS also but it will just increase our another layer in your application that you have to manage separately.

https://www.springboottutorial.com/spring-boot-react-full-stack-crud-maven-application

https://spring.io/guides/tutorials/react-and-spring-data-rest

https://www.devglan.com/react-js/spring-boot-reactjs-crud-example