Annotation processing: generate code, eliminate boilerplate

Annotation processing is a tool built in javac for scanning and processing annotations at compile time. In this talk, we go through the steps of if how it works and how to create one for Android using Kotlin and java.

Transcript

1. ANNOTATION PROCESSING Generate code, eliminate boilerplate @ Rygel Louv
2. Rygel Louv Android dev Makeba.Money GitHub: @Rygelouv Twitter: @Rygellouv Medium: @rygel
3. What do you really know About Wakanda Annotation Processing ?
4. WHAT IS ANNOTATION PROCESSING ? Part of Java compiler Java 5 Improved in Java 6 Scans annotations Process annotations At compile time
5. CODE GENERATION ? Boilerplate problem Generate code .java files or .kt files
6. WHAT ARE THE BENEFITS OF THAT ? Code generator written once Trustable Eliminate boilerplate code Improve productivity Don’t repeat yourself
7. YOU USE IT EVERYDAY! Dagger2 Butterknife Android Annotation library Room persistence library And many more….
8. BUILD AP: WHICH COMPONENTS ? Annotation Processor APT: Annotation Processing Tool android-apt App code with annotated element For Android annotationProcessor kapt
9. STEPS OF AP: HOW DOES IT WORK ? Build starts in javac Starts all annotation processors which are not executed Loop over annotated elements inside the processor Find annotated classes, methods, fields etc. Generated new classes with metadata of founded classes Create new files and write the generated string as class Compiler checks if all annotation processors are executed. If not start next ROUND
10. STEPS OF AP: WHAT ARE ROUNDS FOR APT ?
11. STEPS OF AP: WHAT ARE ROUNDS FOR APT ?
12. STEPS OF AP: WHAT ARE ROUNDS FOR APT ?
13. STEPS OF AP: WHAT ARE ROUNDS FOR APT ?
14. STEPS OF AP: WHAT ARE ROUNDS FOR APT ?
15. BUILD OUR OWN AP: MODULES Create a new project: Android, Java, or Kotlin Create annotation module : Java/Kotlin Create processor module: Java/Kotlin
16. BUILD OUR OWN AP: DEPENDENCIES Annotation module Processor module Application module
17. BUILD OUR OWN AP: CUSTOM ANNOTATIONS Java Kotlin
18. BUILD OUR OWN AP: THE PROCESSOR
19. BUILD OUR OWN AP: THE PROCESSOR Init(): gives tools (Messager and Filer) getSupportedAnnotationType(): returns only our custom annotations getSupportedSourceVersion(): Always return latest java version process(): This were the magic happen. Starts rounding and gives all annotated elements
20. BUILD OUR OWN AP: THE PROCESSOR In the processor you loop over Elements in order to make calculations
21. BUILD OUR OWN AP: TELL JAVAC ABOUT YOUR PROCESSOR Register the processor for it to be found by ServiceLoader Use AutoService
22. BUILD OUR OWN AP: THE RULES Cannot modify existing files Runs in the compile time in its own jvm instance Dependencies are its own and do not impact the main project
23. CODE GENERATION JavaPoet Kotlin Poet Kotlin annotation processing is a bit tricky Temporary solution: Generate .java file in kotlin
24. CODE GENERATION: JAVAPOET AND KOTLINPOET
25. Demo
26. THANK YOU! Wakanda forever!