pl.tlinkowski.unij.api.UniJLoader Maven / Gradle / Ivy
/*
* SPDX-License-Identifier: Apache-2.0
*
* Copyright 2018-2019 Tomasz Linkowski.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package pl.tlinkowski.unij.api;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;
import kotlin.annotations.jvm.Mutable;
import kotlin.annotations.jvm.ReadOnly;
import lombok.experimental.UtilityClass;
import lombok.extern.slf4j.Slf4j;
import pl.tlinkowski.unij.service.api.UniJService;
/**
* Loads UniJ services (used internally by {@link UniJ}).
*
* @author Tomasz Linkowski
*/
@UtilityClass
@Slf4j
final class UniJLoader {
static S load(Class serviceClass) {
@Mutable List services = new ArrayList<>(4);
ServiceLoader.load(serviceClass).forEach(services::add);
validateLoadedServices(services, serviceClass);
return selectService(services, serviceClass);
}
private static void validateLoadedServices(@ReadOnly Collection services, Class serviceClass) {
if (services.isEmpty()) {
throw new UniJException(String.format(
"%s service implementation not found. "
+ "Ensure proper pl.tlinkowski.unij.service.* dependency is on the runtime classpath/modulepath",
serviceClass.getName()
));
}
log.debug("{} service: found {}", serviceClass.getName(), services);
}
private static S selectService(@ReadOnly Collection services, Class serviceClass) {
return selectService(buildPriorityServiceMap(services), serviceClass);
}
private static S selectService(@ReadOnly SortedMap priorityServiceMap, Class serviceClass) {
Integer highestPriority = priorityServiceMap.firstKey();
S highestPriorityService = priorityServiceMap.get(highestPriority);
log.info(
"{} service: selected {} (priority={})",
serviceClass.getName(), className(highestPriorityService), highestPriority
);
return highestPriorityService;
}
@ReadOnly
private static SortedMap buildPriorityServiceMap(@ReadOnly Collection services) {
return services.stream().collect(Collectors.toMap(
UniJLoader::detectPriority, Function.identity(), UniJLoader::throwOnDuplicatePriority, TreeMap::new
));
}
private static int detectPriority(Object service) {
UniJService uniJServiceAnn = service.getClass().getAnnotation(UniJService.class);
if (uniJServiceAnn == null) {
throw new UniJException(String.format(
"Service implementation %s not annotated with @%s", className(service), UniJService.class.getSimpleName()
));
}
return uniJServiceAnn.priority();
}
private static S throwOnDuplicatePriority(S service1, S service2) {
throw new UniJException(String.format(
"%s and %s have the same priority", className(service1), className(service2)
));
}
private static String className(Object object) {
return object.getClass().getName();
}
}