Solve MAVEN multi-project ' Can't find symbols ' issue

First of all, I encountered the problem, first of all, this is a multi-project MAVEN project, it would have been normal package run, but when I joined a controller, an interface and the implementation of the interface class, run again, the console print the following content

My new class all display "Can't find Symbol" error, I Baidu a bit, found a lot of people have encountered this problem, but all said clean or update the project to solve, but I do not. Later asked the great God only to know the original solution is very simple.

This is based on the structure of the multi-project MAVEN project, which is a multi-project MAVEN project app: The control layer that mainly contains the project; Core: contains a variety of interfaces and implementation classes There are also some tool classes, which are interdependent, So the controller inside the app can call the core interface and the tool class, we are packaged to run using the app as a sub-project, and I added a new interface and implementation class in the core project, the direct operation will be error, because the original packaged project does not have these classes, So nature can not find, just need to right-click on the core->run As->maven install, and then start the project again will not error.

Because I have not been in touch with Maven for a long time, so may understand the deviation, welcome correction.