Annotation processor and compiler plugin as code generators.

Hello!I am Oleksandr Radchykov

committed.chinchilla@gmail.combelict

Agenda

1.Motivation2.How to generate code?3.How to annotation processor4.How to create plugin5.Demo

Motivation for code generation

Getting rid of boilerplateclass MyService { private final String name; private final Integer version;

public MyService(String name, Integer version) { this.name = name; This.version = version; }

public String getName() { return name; } public Integer getVersion() { return version; }}

@Getter@RequiredArgsConstructorclass MyService { private final String name; private final Integer version;}

6

Getting rid from annoying code duplicationpublic String validate(Object input) { if (income instanceof String

&& !((String) income).isEmpty()) { return (String) income; } …}

public String validate(Object input) { if (income instanceof String && !income.isEmpty()) { return income; } …}

8

Two ways to generate code

Annotation Processing

▷Java 5+▷Takes java code and generates source files

▷You can not manipulate an existing java code

▷Use the model of processing rounds

Javac Plugin

▷Since Java 8▷Can give us access to AST trees parsed from source code

▷Can be used to add compile-time checks

▷Can run on different phases of compilation process

Annotation processor

1. Implement AbstractProcessor interface

import javax.annotation.processing.AbstractProcessor;

class MyProcessor implements AbstractProcessor {

@Override public boolean process(

Set<? Extends TypeElement> annotations, RoundEnvironment roundEnv) {

/*...*/ }

}

2. Create provider-configuration file

MyProcessor.jar- com/example

- MyProcessor.class- META-INF/services

- javax.annotation.processing.Processor

Provider-configuration file should declare all annotation processors you want to expose.

3. Compilation

$ javac –cp processor.jar \ *sources*.java

Javac plugin

1. Implement Plugin interfaceimport com.sun.source.util.Plugin;

class MyPlugin implements Plugin { @Override public String getName() { return “pluginName”; }

@Override public void init(JavacTask javacTask,

String… strings) { /*...*/ }}

2. Create provider-configuration file

MyPlugin.jar- com/example

- MyPlugin.class- META-INF/services

- com.sun.source.util.Plugin

Provider-configuration file should declare all plugins you want to expose.

3. Compilation

$ javac -Xplugin:PluginName \ –cp /path/to/plugin \

Source.java

Demo

Questions?

Thanks

committed.chinchilla@gmail.combelict