org.meanbean.util.ServiceLoader Maven / Gradle / Ivy
/*-
*
* meanbean
*
* Copyright (C) 2010 - 2020 the original author or authors.
*
* 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.
*
*/
/*
* Copyright 2016 Martin Winandy
*
* 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 org.meanbean.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Constructor;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Objects;
import java.util.ServiceConfigurationError;
import java.util.stream.Stream;
import static java.lang.Thread.currentThread;
import static java.nio.charset.StandardCharsets.UTF_8;
/**
* Alternative service loader that supports constructors with arguments in opposite to {@link java.util.ServiceLoader}.
*
* @param
* Service interface
*/
public final class ServiceLoader {
private static final String SERVICE_PREFIX = "META-INF/services/";
private final Class service;
private final Class[] argumentTypes;
private final ClassLoader classLoader;
/**
* @param service
* Service interface
* @param argumentTypes
* Expected argument types for constructors
*/
public ServiceLoader(Class service, Class... argumentTypes) {
this.service = service;
this.argumentTypes = argumentTypes;
this.classLoader = Stream.of(currentThread().getContextClassLoader(), getClass().getClassLoader())
.filter(Objects::nonNull)
.findFirst()
.orElse(ClassLoader.getSystemClassLoader());
}
public List createAll(Object... arguments) {
try {
Collection classNames = findClassNames(classLoader, service);
List services = new ArrayList<>(classNames.size());
for (String className : classNames) {
services.add(createInstance(className, arguments));
}
return services;
} catch (Exception ex) {
throw new ServiceConfigurationError("Cannot create service instance for " + service.getName(), ex);
}
}
private static Collection findClassNames(ClassLoader classLoader, Class service) throws IOException {
String name = SERVICE_PREFIX + service.getName();
Enumeration urls = classLoader.getResources(name);
Collection classNames = new LinkedHashSet<>();
for (URL url : Collections.list(urls)) {
try (BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), UTF_8))) {
reader.lines()
.map(String::trim)
.filter(line -> !line.isEmpty())
.filter(line -> line.charAt(0) != '#')
.forEach(classNames::add);
}
}
return classNames;
}
private T createInstance(String className, Object... arguments) throws Exception {
Class implementation = Class.forName(className, false, classLoader);
Constructor constructor = implementation.getDeclaredConstructor(argumentTypes);
Object newInstance = constructor.newInstance(arguments);
return service.cast(newInstance);
}
}