/*
* Copyright 2012 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.
*/
package org.gradle.internal.service;
import org.gradle.internal.Factory;
import org.gradle.internal.reflect.DirectInstantiator;
import org.gradle.internal.reflect.Instantiator;
import org.gradle.internal.reflect.ObjectInstantiationException;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.*;
/**
* Uses the Jar service resource specification to locate service implementations.
*/
public class ServiceLocator {
private final List<ClassLoader> classLoaders;
public ServiceLocator(ClassLoader... classLoaders) {
this.classLoaders = Arrays.asList(classLoaders);
}
public <T> T get(Class<T> serviceType) throws UnknownServiceException {
return getFactory(serviceType).create();
}
public <T> List<T> getAll(Class<T> serviceType) throws UnknownServiceException {
List<ServiceFactory<T>> factories = findFactoriesForServiceType(serviceType);
ArrayList<T> services = new ArrayList<T>();
for (ServiceFactory<T> factory : factories) {
services.add(factory.create());
}
return services;
}
public <T> ServiceFactory<T> getFactory(final Class<T> serviceType) throws UnknownServiceException {
ServiceFactory<T> factory = findFactory(serviceType);
if (factory == null) {
throw new UnknownServiceException(serviceType, String.format("Could not find meta-data resource 'META-INF/services/%s' for service '%s'.", serviceType.getName(), serviceType.getName()));
}
return factory;
}
/**
* Locates a factory for a given service. Returns null when no service implementation is available.
*/
public <T> ServiceFactory<T> findFactory(Class<T> serviceType) {
List<ServiceFactory<T>> factories = findFactoriesForServiceType(serviceType);
if (factories.isEmpty()) {
return null;
}
return factories.get(0);
}
private <T> List<ServiceFactory<T>> findFactoriesForServiceType(Class<T> serviceType) {
List<Class<? extends T>> implementationClasses;
try {
implementationClasses = findServiceImplementations(serviceType);
} catch (ServiceLookupException e) {
throw e;
} catch (Exception e) {
throw new ServiceLookupException(String.format("Could not determine implementation classes for service '%s'.", serviceType.getName()), e);
}
List<ServiceFactory<T>> factories = new ArrayList<ServiceFactory<T>>();
for (Class<? extends T> implementationClass : implementationClasses) {
factories.add(new ServiceFactory<T>(serviceType, implementationClass));
}
return factories;
}
private <T> List<Class<? extends T>> findServiceImplementations(Class<T> serviceType) throws IOException {
String resourceName = "META-INF/services/" + serviceType.getName();
Set<String> implementationClassNames = new HashSet<String>();
List<Class<? extends T>> implementations = new ArrayList<Class<? extends T>>();
for (ClassLoader classLoader : classLoaders) {
Enumeration<URL> resources = classLoader.getResources(resourceName);
while (resources.hasMoreElements()) {
URL resource = resources.nextElement();
List<String> implementationClassNamesFromResource;
try {
implementationClassNamesFromResource = extractImplementationClassNames(resource);
if (implementationClassNamesFromResource.isEmpty()) {
throw new RuntimeException(String.format("No implementation class for service '%s' specified.", serviceType.getName()));
}
} catch (Exception e) {
throw new ServiceLookupException(String.format("Could not determine implementation class for service '%s' specified in resource '%s'.", serviceType.getName(), resource), e);
}
for (String implementationClassName : implementationClassNamesFromResource) {
if (implementationClassNames.add(implementationClassName)) {
try {
Class<?> implClass = classLoader.loadClass(implementationClassName);
if (!serviceType.isAssignableFrom(implClass)) {
throw new RuntimeException(String.format("Implementation class '%s' is not assignable to service class '%s'.", implementationClassName, serviceType.getName()));
}
implementations.add(implClass.asSubclass(serviceType));
} catch (Exception e) {
throw new ServiceLookupException(String.format("Could not load implementation class '%s' for service '%s' specified in resource '%s'.", implementationClassName, serviceType.getName(), resource), e);
}
}
}
}
}
return implementations;
}
private List<String> extractImplementationClassNames(URL resource) throws IOException {
InputStream inputStream = resource.openStream();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));
List<String> implemetationClassNames = new ArrayList<String>();
String line;
while ((line = reader.readLine()) != null) {
line = line.replaceAll("#.*", "").trim();
if (line.length() > 0) {
implemetationClassNames.add(line);
}
}
return implemetationClassNames;
} finally {
inputStream.close();
}
}
public static class ServiceFactory<T> implements Factory<T> {
private final Class<T> serviceType;
private final Class<? extends T> implementationClass;
public ServiceFactory(Class<T> serviceType, Class<? extends T> implementationClass) {
this.serviceType = serviceType;
this.implementationClass = implementationClass;
}
public Class<? extends T> getImplementationClass() {
return implementationClass;
}
public T create() {
return newInstance();
}
public T newInstance(Object... params) {
Instantiator instantiator = new DirectInstantiator();
try {
return instantiator.newInstance(implementationClass, params);
} catch (ObjectInstantiationException t) {
throw new RuntimeException(String.format("Could not create an implementation of service '%s'.", serviceType.getName()), t);
}
}
}
}