Curso bom de Java com certificado.

Oficial - Oracle
Notícias e recursos mais recentes para desenvolvedores Java.
https://dev.java/
https://developer.oracle.com/

IBM
Develop modern applications with the open Java ecosystem.
https://developer.ibm.com/languages/java/

Microsoft
https://docs.microsoft.com/pt-br/java/
https://devblogs.microsoft.com/java/
https://cloudblogs.microsoft.com/opensource/tag/java/

Amazon (AWS)
Java na AWS
https://aws.amazon.com/pt/developer/language/java/