Javaアノテーション処理とビルダーの作成

@SupportedAnnotationTypes(
  "com.baeldung.annotation.processor.BuilderProperty")
@SupportedSourceVersion(SourceVersion.RELEASE__8)
@AutoService(Processor.class)
public class BuilderProcessor extends AbstractProcessor {

    @Override
    public boolean process(Set<? extends TypeElement> annotations,
      RoundEnvironment roundEnv) {
        return false;
    }
}

@Override
public boolean process(Set<? extends TypeElement> annotations,
  RoundEnvironment roundEnv) {

    for (TypeElement annotation : annotations) {
        Set<? extends Element> annotatedElements
          = roundEnv.getElementsAnnotatedWith(annotation);

       //...
    }

    return true;
}

Map<Boolean, List<Element>> annotatedMethods = annotatedElements.stream().collect(
  Collectors.partitioningBy(element ->
    ((ExecutableType) element.asType()).getParameterTypes().size() == 1
    && element.getSimpleName().toString().startsWith("set")));

List<Element> setters = annotatedMethods.get(true);
List<Element> otherMethods = annotatedMethods.get(false);

otherMethods.forEach(element ->
  processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR,
    "@BuilderProperty must be applied to a setXxx method "
      + "with a single argument", element));

if (setters.isEmpty()) {
    continue;
}

String className = ((TypeElement) setters.get(0)
  .getEnclosingElement()).getQualifiedName().toString();

Map<String, String> setterMap = setters.stream().collect(Collectors.toMap(
    setter -> setter.getSimpleName().toString(),
    setter -> ((ExecutableType) setter.asType())
      .getParameterTypes().get(0).toString()
));

JavaFileObject builderFile = processingEnv.getFiler()
  .createSourceFile(builderClassName);
try (PrintWriter out = new PrintWriter(builderFile.openWriter())) {
   //writing generated file to out ...
}

private void writeBuilderFile(
  String className, Map<String, String> setterMap)
  throws IOException {

    String packageName = null;
    int lastDot = className.lastIndexOf('.');
    if (lastDot > 0) {
        packageName = className.substring(0, lastDot);
    }

    String simpleClassName = className.substring(lastDot + 1);
    String builderClassName = className + "Builder";
    String builderSimpleClassName = builderClassName
      .substring(lastDot + 1);

    JavaFileObject builderFile = processingEnv.getFiler()
      .createSourceFile(builderClassName);

    try (PrintWriter out = new PrintWriter(builderFile.openWriter())) {

        if (packageName != null) {
            out.print("package ");
            out.print(packageName);
            out.println(";");
            out.println();
        }

        out.print("public class ");
        out.print(builderSimpleClassName);
        out.println(" {");
        out.println();

        out.print("    private ");
        out.print(simpleClassName);
        out.print(" object = new ");
        out.print(simpleClassName);
        out.println("();");
        out.println();

        out.print("    public ");
        out.print(simpleClassName);
        out.println(" build() {");
        out.println("        return object;");
        out.println("    }");
        out.println();

        setterMap.entrySet().forEach(setter -> {
            String methodName = setter.getKey();
            String argumentType = setter.getValue();

            out.print("    public ");
            out.print(builderSimpleClassName);
            out.print(" ");
            out.print(methodName);

            out.print("(");

            out.print(argumentType);
            out.println(" value) {");
            out.print("        object.");
            out.print(methodName);
            out.println("(value);");
            out.println("        return this;");
            out.println("    }");
            out.println();
        });

        out.println("}");
    }
}

javac com/baeldung/annotation/processor/BuilderProcessor
javac com/baeldung/annotation/processor/BuilderProperty

javac -processor com.baeldung.annotation.processor.MyProcessor Person.java

javac -processor package1.Processor1,package2.Processor2 SourceFile.java

<build>
    <plugins>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <encoding>UTF-8</encoding>
                <generatedSourcesDirectory>${project.build.directory}
                 /generated-sources/</generatedSourcesDirectory>
                <annotationProcessors>
                    <annotationProcessor>
                        com.baeldung.annotation.processor.BuilderProcessor
                    </annotationProcessor>
                </annotationProcessors>
            </configuration>
        </plugin>

    </plugins>
</build>

com.baeldung.annotation.processor.BuilderProcessor

package1.Processor1
package2.Processor2
package3.Processor3

----[ERROR]Bad service configuration file, or exception thrown while
constructing Processor object: javax.annotation.processing.Processor:
Provider com.baeldung.annotation.processor.BuilderProcessor not found
----

@AutoService(Processor.class)
public BuilderProcessor extends AbstractProcessor {
   //...
}