ANNOTATION PROCESSING Generate code, eliminate boilerplate @ Rygel Louv 

Rygel Louv Android dev Makeba.Money GitHub: @Rygelouv Twitter: @Rygellouv Medium: @rygel 

What do you really know About Wakanda Annotation Processing ? 

WHAT IS ANNOTATION PROCESSING ? Part of Java compiler Java 5 Improved in Java 6 Scans annotations Process annotations At compile time 

CODE GENERATION ? Boilerplate problem Generate code .java files or .kt files 

WHAT ARE THE BENEFITS OF THAT ? Code generator written once Trustable Eliminate boilerplate code Improve productivity Don’t repeat yourself 

YOU USE IT EVERYDAY! Dagger2 Butterknife Android Annotation library Room persistence library And many more…. 

BUILD AP: WHICH COMPONENTS ? Annotation Processor APT: Annotation Processing Tool android-apt App code with annotated element For Android annotationProcessor kapt 

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 

STEPS OF AP: WHAT ARE ROUNDS FOR APT ? 

STEPS OF AP: WHAT ARE ROUNDS FOR APT ? 

STEPS OF AP: WHAT ARE ROUNDS FOR APT ? 

STEPS OF AP: WHAT ARE ROUNDS FOR APT ? 

STEPS OF AP: WHAT ARE ROUNDS FOR APT ? 

BUILD OUR OWN AP: MODULES Create a new project: Android, Java, or Kotlin Create annotation module : Java/Kotlin Create processor module: Java/Kotlin 

BUILD OUR OWN AP: DEPENDENCIES Annotation module Processor module Application module 

BUILD OUR OWN AP: CUSTOM ANNOTATIONS Java Kotlin 

BUILD OUR OWN AP: THE PROCESSOR 

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 

BUILD OUR OWN AP: THE PROCESSOR In the processor you loop over Elements in order to make calculations 

BUILD OUR OWN AP: TELL JAVAC ABOUT YOUR PROCESSOR Register the processor for it to be found by ServiceLoader Use AutoService 

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 

CODE GENERATION JavaPoet Kotlin Poet Kotlin annotation processing is a bit tricky Temporary solution: Generate .java file in kotlin 

CODE GENERATION: JAVAPOET AND KOTLINPOET 

Demo 

THANK YOU! Wakanda forever!