compile.sh

mvn clean package

Dummy.java

public class Dummy {

	private String name;

	@HelloWorld
	public String getName() {
		return this.name;
	}

	public static void main(String... args) {
		new Dummy().getName();
	}
}

HelloProcessor.java

import java.util.Set;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;

import com.sun.tools.javac.model.JavacElements;
import com.sun.tools.javac.processing.JavacProcessingEnvironment;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCExpression;
import com.sun.tools.javac.tree.JCTree.JCLiteral;
import com.sun.tools.javac.tree.TreeMaker;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.util.Name;

@SupportedAnnotationTypes({ "HelloWorld" })
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class HelloProcessor extends AbstractProcessor {

	@Override
	public boolean process(
			Set<? extends TypeElement> annotations, 
			RoundEnvironment roundEnv) {
		
		if (roundEnv.processingOver()) {
			return false;
		}
		
		JavacProcessingEnvironment environment 
			= (JavacProcessingEnvironment) processingEnv;
		
		Context context 
			= environment.getContext();
		TreeMaker maker 
			= TreeMaker.instance(context);
		JavacElements elemUtils 
			= (JavacElements) processingEnv.getElementUtils();
		
		Class<HelloWorld> clazz = HelloWorld.class;
		Set<? extends Element> elements 
			= roundEnv.getElementsAnnotatedWith(clazz);
		
		for (Element element : elements) {
			JCTree tree = elemUtils.getTree(element);
			JCTree.JCMethodDecl mDecl 
				= (JCTree.JCMethodDecl) tree;
			
			injectHelloWorld(maker, elemUtils, mDecl);
		}
		
		return false;
	}

	private void injectHelloWorld(
			TreeMaker maker, 
			JavacElements elemUtils, 
			JCTree.JCMethodDecl mDecl) {
		
		maker.pos = mDecl.pos;
		
		List<JCExpression> nil = List.<JCTree.JCExpression> nil();
		Name system = elemUtils.getName("System");
		Name out = elemUtils.getName("out");
		Name _println = elemUtils.getName("println");
		JCLiteral helloworld = maker.Literal("Hello world");
		
		mDecl.body = maker.Block(0,List.of(
			maker.Exec(maker.Apply(nil,
				maker.Select(maker.Select(
					maker.Ident(
					system),
					out),
					_println),
				List.<JCTree.JCExpression> of(helloworld))),
			mDecl.body)
		);
	}
}

HelloWorld.java

public @interface  {
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>freestrings.apt</groupId>
	<artifactId>apt-playground</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>jar</packaging>

	<build>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>2.3.2</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
					<!-- Disable annotation processing for ourselves. -->
					<compilerArgument>-proc:none</compilerArgument>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<dependency>
			<groupId>com.sun</groupId>
			<artifactId>tools</artifactId>
			<version>1.8.0</version>
			<scope>system</scope>
			<systemPath>/usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar</systemPath>
		</dependency>
	</dependencies>
</project>

run.sh

javac -cp target/apt-playground-1.0-SNAPSHOT.jar -processor HelloProcessor Dummy.java