The source of learning is learning from others. Here some official published papers

Magazines.

Recommended magazines:

• Java Magazin (german)
• Objekt Spektrum (german)
• Informatik-Spektrum (german)
• c’t (german)

Books

Highlights of books:

• Code Complete 2
• Effective Java
• Concurrency in Practice
• Pragmatic Programmer
• Refactoring
• Refactoring to Patterns
• Refactorings in Großprojekten (german)
• xUnit Test Patterns
• Continous Integration
• Design Patterns, GoF
• Head first Design Patterns
• Enterprise Integration Patterns
• Patterns of Enterprise Application Architecture
• Rest und HTTP (german)
• Domain Driven Design
• Why Programs fail
• Softwarewartung
• The Mythical Man-Month
• From Adrenaline Junkies to Template Zombies
• Pragmatic Thinking and Learning
• How Coders work
• Soft Skills für Softwareentwickler (german)