com.vmware.photon.controller.model.util.StartServicesHelper Maven / Gradle / Ivy
/*
* Copyright (c) 2015-2016 VMware, Inc. All Rights Reserved.
*
* 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 com.vmware.photon.controller.model.util;
import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.function.Supplier;
import com.vmware.xenon.common.FactoryService;
import com.vmware.xenon.common.Service;
import com.vmware.xenon.common.ServiceHost;
import com.vmware.xenon.common.UriUtils;
/**
* The goal of this helper class is to ease the start of family of services (such as
* {@link com.vmware.photon.controller.model.PhotonModelServices}) and at the same time expose their
* public links.
*
*
* Impl notes: As of now the approach is to create {@code public static String[] LINKS} var holding
* services links and {@code public static void startServices(ServiceHost host)} method starting all
* the services. And the expectation is that the set of links and the set of started services should
* be the same. In order to enforce that we introduce {@link ServiceMetadata} that is used to
* calculate the links and start the services, thus the client of the class is focused on just
* describing its set of services.
*/
public class StartServicesHelper {
/**
* Use this method to get the set of service links.
*
* @see com.vmware.photon.controller.model.PhotonModelServices#LINKS
*/
public static String[] getServiceLinks(ServiceMetadata[] servicesMetadata) {
return Arrays.stream(servicesMetadata)
.map(ServiceMetadata::getLink)
.toArray(String[]::new);
}
/**
* Use this method to start the set of services.
*
* @see com.vmware.photon.controller.model.PhotonModelServices#startServices(ServiceHost)
*/
public static void startServices(ServiceHost host, ServiceMetadata[] servicesMetadata) {
Arrays.stream(servicesMetadata).forEach(serviceDesc -> serviceDesc.start(host));
}
/**
* A meta-data describing a service including:
*
* - service type (such as service or factory)
* - service class
* - service instantiation logic (applicable for factory services)
*
*/
public static class ServiceMetadata {
/**
* Create meta-data for a {@link Service}.
*/
public static ServiceMetadata service(Class serviceClass) {
final ServiceMetadata serviceDesc = new ServiceMetadata();
serviceDesc.isServiceOrFactory = true;
serviceDesc.serviceClass = serviceClass;
return serviceDesc;
}
/**
* Create meta-data for a {@link FactoryService}.
*/
public static ServiceMetadata factoryService(
Class serviceClass,
Supplier factoryCreator) {
final ServiceMetadata serviceDesc = new ServiceMetadata();
serviceDesc.isServiceOrFactory = false;
serviceDesc.serviceClass = serviceClass;
serviceDesc.factoryCreator = factoryCreator;
return serviceDesc;
}
/**
* Create meta-data for a {@link FactoryService}.
*/
public static ServiceMetadata factoryService(Class serviceClass) {
return factoryService(serviceClass, null);
}
// true = service; false = factory service
private boolean isServiceOrFactory;
private Class serviceClass;
private Supplier factoryCreator;
/**
* Get (through reflection by analogy with UriUtils.buildFactoryUri) the SELF_LINK of a
* service or the FACTORY_LINK of a factory service.
*/
public String getLink() {
String selfLinkOrFactoryLinkName = this.isServiceOrFactory
? UriUtils.FIELD_NAME_SELF_LINK
: UriUtils.FIELD_NAME_FACTORY_LINK;
try {
Field selfLinkOrFactoryLink = this.serviceClass
.getDeclaredField(selfLinkOrFactoryLinkName);
if (selfLinkOrFactoryLink != null) {
selfLinkOrFactoryLink.setAccessible(true);
return selfLinkOrFactoryLink.get(null).toString();
}
} catch (Exception e) {
}
throw new IllegalAccessError(String.format(
"'%s' service does not have public static '%s' field",
this.serviceClass,
selfLinkOrFactoryLinkName));
}
/**
* Start the service considering its type.
*/
public void start(ServiceHost serviceHost) {
if (this.isServiceOrFactory) {
serviceHost.startService(newServiceInstance());
} else {
if (this.factoryCreator == null) {
serviceHost.startFactory(newServiceInstance());
} else {
serviceHost.startFactory(this.serviceClass, this.factoryCreator);
}
}
}
private Service newServiceInstance() {
try {
return this.serviceClass.newInstance();
} catch (InstantiationException | IllegalAccessException e) {
throw new IllegalAccessError(
"Failed to create an instance of " + this.serviceClass);
}
}
}
}