For IntelliJ IDEA 12+ releases we can build automatically the edited sources if we are using the external compiler option. The only thing needed is to check the option "Build project automatically ", located under "Compiler" settings:
Also, if you would like to hot deploy, while the application is running or if you are using spring boot devtools you should enable the compiler.automake.allow.when.app.running from registry too. This will automatically compile your changes.
For versions greater than 2021.2, we need check 'Allow auto-make to start even id the development application is currently running' option:
For versions older than 2021.2:
Using Ctrl+Shift+A (or ⌘+Shift+A on Mac) type Registry once the registry windows is open, locate and enable compiler.automake.allow.when.app.running, see here:
参考：jakarta ee - Intellij IDEA Java classes not auto compiling on save - Stack Overflow