According to the internal strength of the process: relational database, domain-driven design, design pattern, algorithm, object-oriented programming OOP(SOLID), thread safety, event-driven, test-driven development, dependency injection framework and so on.
For students who are new to Java and interested in back-end development, they need to focus on the following parts:
Fundamentals: such as computer systems, algorithms, compilation principles, etc.
Web development: mainly related to Web development, including HTML/CSS/js (home page), Servlet/JSP(J2EE) and MySQL (database). Their learning order should be from front to back, so the first thing to learn should be HTML/CSS/JS (home page).
J2EE: What you need to learn is the Servlet/JSP(J2EE) part, which is a part that Java back-end development must be very proficient in, so this part is the most demanding part of these three parts. Regarding the selection of some videos of Servlet/Jsp, Ma Shibing's videos are recognized by the industry.
Finally, you need to learn to use the database. Mysql is a good entry choice, and the mainstream relational database in Java field is mysql. This part is usually encountered when learning Servlet/Jsp, and JDBC is a database-related part. You should not only learn to use JDBC to operate the database, but also learn to use database client tools, such as navicat and sqlyog. You can choose between them.
Development framework: SSM framework is the mainstream at present, namely spring, springmvc and mybatis. You need to learn how to build these three frameworks and use them to make a simple Web project. You don't have to understand what those configurations mean and why you do it. This is for you to understand later. But you must be able to build a Web framework quickly by using these three. You can record the process of your first construction. Trust me, you will use it. Also, in the process of building SSM, you may often come into contact with a tool called maven. This tool is almost indispensable for your future work, so you can also learn something about maven during the process of building SSM. At this stage, you only need to know the basic usage of maven on the internet, and some high-end usage will gradually come into contact with you as your work experience increases.
Therefore, you need to look at the source code of some classes of JDK, including the source code of the framework you use. The premise that these source codes can be understood is that you must have a good understanding of design patterns. Otherwise, when you look at the source code, there will always be such questions. Why is this code written like this? Why define this interface? It seems redundant. It can also be seen that these learning processes are interlocking. If you fail any stage, then you really can't keep up, or it is slow step by step. And I am very responsible to tell you that at this stage, I have learned far more than what is listed here.
To sum up, at this stage, what you need to do is to have a deep understanding of the underlying Java and Java class libraries (for example, the book concurrent is Java, and the contents of java.concurrent are contracted out), that is, the related contents of JVM and JDK. Moreover, you should have a deeper understanding of the framework you are using. It is recommended to read the source code or official documents.