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Special mention to @jmpergar

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Let’ s move on!

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tooling automatize as much as you can

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why annotation processors?

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1. From runtime to compile time 2. Avoid reflection 3. Eliminate boilerplate

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Added in JDK 5 APT and Rich public API on JDK 6 Standardized through JSR 269

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APT is a powerful tool

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doable: 1. Scan sources for annotations 2. Generate source files

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not doable: 1. Inject code into / modify sources

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Reflective APIs: 1. Standard (Java Reflection API) 2. Mirror based ones (Java Mirror API) ObjectMirror carMirror = Reflection.reflect(myCar);

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before compiling, ServiceLoader runs all the processors using source files as input

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¿how to register a processor?

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Option 1: static file declaring its path

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include qualified name of your processor class

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Option 2: AutoService library

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processing rounds

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creating a custom processor

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Extend AbstractProcessor and override some methods

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get utility classes from processingEnvironment

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4 phases per round

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1. Scan for annotations 2. Static validation 3. Parse to meta-models 4. Code generation

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1. Scan for annotations get a Set of annotated Elements

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1. Executable Element (method) 2. Type Element (class) 3. Variable Element (fields, method params)

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2. Static Validation get a Set of annotated Elements

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3. Parse to meta-models create meta-models to increase simplicity

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4. Code generation JavaPoet: Based on specs

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https://github.com/square/javapoet

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how to test to avoid compiling the whole project many times?

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Truth + compile-testing test validation code while developing it

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test code generation

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base classes to improve readability

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debug is possible at compile time

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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 {

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● 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

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questions?