Codio
Skills you'll gain: Apache Maven, JSON, JUnit, Java Programming, Java, Restful API, Integrated Development Environments, Programming Principles, Data Structures, Object Oriented Programming (OOP), Network Protocols, Unit Testing, Style Guides
Intermediate · Course · 1 - 4 Weeks

LearnQuest
Skills you'll gain: Hibernate (Java), Object-Relational Mapping, Java Platform Enterprise Edition (J2EE), Data Access, Data Persistence, Java, Relational Databases, Data Mapping, JUnit, Query Languages, Transaction Processing
Intermediate · Course · 1 - 4 Weeks
Skills you'll gain: OS Process Management, Operating Systems, System Programming, Performance Tuning, Data Structures, Debugging
Advanced · Course · 1 - 4 Weeks

EDUCBA
Skills you'll gain: File I/O, Object Oriented Programming (OOP), Java Programming, Data Structures, Data Persistence, Programming Principles
Intermediate · Course · 1 - 4 Weeks

Duke University
Skills you'll gain: Object Oriented Programming (OOP), File I/O, Encryption, Data Structures, Java, Algorithms, Cryptography, Computer Programming, Software Design, Web Analytics and SEO, Debugging
Beginner · Course · 1 - 3 Months

Skills you'll gain: Object Oriented Design, Software Design Patterns, Functional Design, Maintainability
Intermediate · Course · 3 - 6 Months

Skills you'll gain: Spring Framework, Java, Application Frameworks, Object Oriented Design, Object Oriented Programming (OOP), Software Design Patterns, Extensible Markup Language (XML), Dependency Analysis
Mixed · Course · 1 - 4 Weeks

Skills you'll gain: Object Oriented Programming (OOP), Java, Software Development Life Cycle, Program Development, Computer Programming, Development Environment, Software Development, Integrated Development Environments, Command-Line Interface, Linux Commands
Beginner · Course · 1 - 4 Weeks

Skills you'll gain: Programming Principles
Intermediate · Course · 1 - 4 Weeks

Skills you'll gain: Data Structures, Graph Theory, Algorithms, Java, Theoretical Computer Science, Performance Tuning
Intermediate · Course · 1 - 4 Weeks

Skills you'll gain: Application Development, UI Components
Intermediate · Course · 1 - 4 Weeks

Skills you'll gain: Apache Maven, Java Platform Enterprise Edition (J2EE), Hibernate (Java), Unit Testing, Docker (Software), Software Design Patterns, Object-Relational Mapping
Intermediate · Course · 1 - 3 Months