ServiceProviderAnnotationProcessor.java

/*
 * Copyright 2011 Blazebit
 */
package com.blazebit.apt.service;

import com.blazebit.apt.AnnotationProcessingUtils;
import java.io.BufferedWriter;
import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
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.AnnotationMirror;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
import javax.tools.Diagnostic;
import javax.tools.FileObject;
import javax.tools.StandardLocation;

/**
 * Constraint Validator classes must be available in compiled form!
 * 
 * @author Christian Beikov
 * @since 0.1.2
 */
@SupportedAnnotationTypes("com.blazebit.apt.service.ServiceProvider")
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class ServiceProviderAnnotationProcessor extends AbstractProcessor {

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

		Map<String, List<String>> serviceProviders = new HashMap<String, List<String>>();

		for (Element e : roundEnv
				.getElementsAnnotatedWith(ServiceProvider.class)) {
			TypeElement typeElement = (TypeElement) e;
			AnnotationMirror annotation = AnnotationProcessingUtils
					.findAnnotationMirror(processingEnv, typeElement,
							ServiceProvider.class);

			if (annotation == null) {
				// Workaround a strange bug...
				continue;
			}

			String service = AnnotationProcessingUtils
					.getAnnotationElementValue(processingEnv, annotation,
							"value").getValue().toString();

			List<String> providers = serviceProviders.get(service);

			if (providers == null) {
				providers = new ArrayList<String>();
				serviceProviders.put(service, providers);
			}

			providers.add(typeElement.getQualifiedName().toString());
		}

		String serviceFile = null;

		try {
			for (Map.Entry<String, List<String>> entry : serviceProviders
					.entrySet()) {
				serviceFile = entry.getKey();
				FileObject providerFileObject = processingEnv.getFiler()
						.createResource(StandardLocation.SOURCE_OUTPUT, "",
								"META-INF/services/" + serviceFile);

				List<String> services = entry.getValue();
				BufferedWriter writer = null;

				try {
					writer = new BufferedWriter(providerFileObject.openWriter());

					for (int i = 0; i < services.size(); i++) {
						writer.append(services.get(i)).append('\n');
					}
				} finally {
					if (writer != null) {
						writer.close();
					}
				}
			}
		} catch (Exception ex) {
			ByteArrayOutputStream baos = new ByteArrayOutputStream();
			ex.printStackTrace(new PrintStream(baos));
			processingEnv.getMessager().printMessage(
					Diagnostic.Kind.ERROR,
					"Could not create service file '" + serviceFile + "'\n"
							+ baos.toString());
			return false;
		}

		return true;
	}
}