[Java] Annotation Processor

Annotation Processor

설명

• 컴파일 시점에 Annotation 기반으로 코드를 변경하거나 생성하는 방법을 말한다.
• lombok이 Annotation Processor로 만들어졌다.
• 아래 예제는 Student 클래스를 베이스로 StudentWithGetter 클래스를 만드는 예제
• 다중 모듈 방식으로 프로젝트를 구성한다.
  • https://sg-choi.tistory.com/536

annotation-processor-example 모듈

설명

• 최상위 모듈
• plugin 모듈과 application 모듈 관계 설정을 위해 필요

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>annotation-processor-example</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <modules>
        <module>plugin</module>
        <module>application</module>
    </modules>
</project>

plugin 모듈

설명

• Annotation Processor 로직을 갖는 모듈

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>plugin</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <java.version>11</java.version>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
                <executions>
                    <execution>
                        <id>default-compile</id>
                        <configuration>
                            <compilerArgument>-proc:none</compilerArgument>
                        </configuration>
                    </execution>
                    <execution>
                        <id>compile-project</id>
                        <phase>compile</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Getter

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.SOURCE)
public @interface Getter {
}

GetterProcessor

@SupportedAnnotationTypes("org.example.plugin.getter.Getter")
public class GetterProcessor extends AbstractProcessor {
    @Override
    public SourceVersion getSupportedSourceVersion() {
        return SourceVersion.latestSupported();
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnvironment) {
        for (TypeElement annotation : annotations) {
            Element type = roundEnvironment.getElementsAnnotatedWith(annotation).stream().findFirst().orElseGet(null);
            String classFullName = type.toString();
            String packageName = classFullName.substring(0, classFullName.lastIndexOf("."));
            String className = classFullName.substring(packageName.length() + 1);
            String newClassName = className + "WithGetter";

            StringBuilder code = new StringBuilder();
            code.append("package ").append(packageName).append(";\n\n");
            code.append("public class ").append(newClassName).append(" {\n");

            type.getEnclosedElements().stream()
                .filter(e -> e.getKind() == ElementKind.FIELD)
                .forEach(field -> {
                    code.append("    ");

                    Optional<Modifier> modifier = field.getModifiers().stream().findFirst();
                    if (modifier.isPresent()) {
                        code.append(modifier.get().toString().toLowerCase()).append(" ");
                    }

                    code.append(field.asType().toString()).append(" ").append(field.toString()).append(";\n\n");

                    code.append("    ").append("public ").append(field.asType().toString()).append(" ").append(field.toString()).append("() {\n");
                    code.append("        ").append("return ").append(field.toString()).append(";\n");
                    code.append("    }\n");
                });

            code.append("}\n");

            try  {
                JavaFileObject builderFile = processingEnv.getFiler().createSourceFile(packageName + "." + newClassName);

                try (PrintWriter out = new PrintWriter(builderFile.openWriter())) {
                    out.println(code);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return true;
    }
}

javax.annotation.processing.Processor

• Processor 목록을 명시하는 파일
• 패키지명을 포함한 클래스명을 작성한다.
• Processor가 여러개일 경우 개행으로 구분하여 나열할 수 있다.
• 경로 : plugin/src/main/resources/META-INF/services/javax.annotation.processing.Processor

org.example.plugin.getter.GetterProcessor

application 모듈

설명

• Annotation Processor 기능을 활용하는 모듈
• Student 클래스를 두고 컴파일시 Processor를 통해 StudentWithGetter 클래스를 만들어 사용한다.

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>application</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <java.version>11</java.version>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <!-- Annotation Processor 모듈 의존성 추가 -->
    <dependencies>
        <dependency>
            <groupId>org.example</groupId>
            <artifactId>plugin</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
</project>

Student

@Getter
public class Student {
    private String name;
    private int age;
}

StudentWithGetter

• 컴파일한 후 target/classes 디렉토리 하위에 StudentWithGetter.class 파일이 생성되었는지 확인한다.

public class StudentWithGetter {
    private String name;
    private int age;

    public StudentWithGetter() {
    }

    public String name() {
        return this.name;
    }

    public int age() {
        return this.age;
    }
}

Application

public class Application {
    public static void main(String[] args) {
        StudentWithGetter student = new StudentWithGetter();
        student.name();
    }
}

참고

• https://andole98.github.io/java/java-annotation-process
• https://free-strings.blogspot.com/2015/12/lombok.html
• https://www.javacodegeeks.com/2015/09/java-annotation-processors.html
• https://www.charlezz.com/?p=1167