CUSTOM ANNOTATION PROCESSORS FOR YOUR PRODUCTION CODE

The annotation processing tool (APT) was released into the JDK 5, but we did not put enough attention to it in order to exploit its potential. Today, annotation processors are part of many well known libraries that we use everyday in our professional code. On this talk we will learn how to code our custom annotation processor and to start looking at it as a very useful tool to reduce overhead in our production code. Because many recurrent problems could get solved using annotation processors!

Transcript

4. Special mention to @jmpergar
5. Let’ s move on!
6. tooling automatize as much as you can
7. why annotation processors?
8. 1. From runtime to compile time 2. Avoid reflection 3. Eliminate boilerplate
9. Added in JDK 5 APT and Rich public API on JDK 6 Standardized through JSR 269
10. APT is a powerful tool
11. doable: 1. Scan sources for annotations 2. Generate source files
12. not doable: 1. Inject code into / modify sources
13. Reflective APIs: 1. Standard (Java Reflection API) 2. Mirror based ones (Java Mirror API) ObjectMirror carMirror = Reflection.reflect(myCar);
14. before compiling, ServiceLoader runs all the processors using source files as input
15. ¿how to register a processor?
16. Option 1: static file declaring its path
17. include qualified name of your processor class
18. Option 2: AutoService library
19. processing rounds
20. creating a custom processor
21. Extend AbstractProcessor and override some methods
23. get utility classes from processingEnvironment
24. 4 phases per round
25. 1. Scan for annotations 2. Static validation 3. Parse to meta-models 4. Code generation
26. 1. Scan for annotations get a Set of annotated Elements
27. 1. Executable Element (method) 2. Type Element (class) 3. Variable Element (fields, method params)
28. 2. Static Validation get a Set of annotated Elements
31. 3. Parse to meta-models create meta-models to increase simplicity
33. 4. Code generation JavaPoet: Based on specs
35. https://github.com/square/javapoet
36. how to test to avoid compiling the whole project many times?
37. Truth + compile-testing test validation code while developing it
38. test code generation
40. base classes to improve readability
42. debug is possible at compile time
43. 1. divide your library in separate modules (compiler, public api) 2. include other libraries just for compile time (provided) 3. war plugin for pure java modules public final recommendations {
44. • AutoService https://github.com/google/auto/tree/master/service • Truth https://github.com/google/truth • Compile-Testing https://github.com/google/compile-testing • JavaPoet https://github.com/square/javapoet • Great threads about creating your custom processor http://hannesdorfmann.com/annotation-processing/annotationprocessing101 • https://deors.wordpress.com/2011/09/26/annotation-types/ https://deors.wordpress.com/2011/10/08/annotation-processors/ https://deors.wordpress.com/2011/10/31/annotation-generators/ • Some official (SUN) info about both types of reflective APIs http://bracha.org/mirrors.pdf Resources and recommended reads
45. questions?