[spring-cloud: NamedContextFactory & ClientFactoryObjectProvider]-源码阅读

依赖

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-commons</artifactId>
    <version>4.3.0</version>
</dependency>

源码

NamedContextFactory

NamedContextFactory 类通过创建多个子上下文并为每个子上下文定义不同的配置，提供了灵活的 Spring 上下文管理方式。

/**
 * Creates a set of child contexts that allows a set of Specifications to define the beans
 * in each child context. Ported from spring-cloud-netflix FeignClientFactory and
 * SpringClientFactory
 *
 * @param <C> specification
 * @author Spencer Gibb
 * @author Dave Syer
 * @author Tommy Karlsson
 * @author Olga Maciaszek-Sharma
 */
public abstract class NamedContextFactory<C extends NamedContextFactory.Specification> implements DisposableBean, ApplicationContextAware {

	// 子容器初始化
	private final Map<String, ApplicationContextInitializer<GenericApplicationContext>> applicationContextInitializers;

	private final String propertySourceName;

	private final String propertyName;

	// 子容器集合
	private final Map<String, GenericApplicationContext> contexts = new ConcurrentHashMap<>();
	// 子容器配置
	private final Map<String, C> configurations = new ConcurrentHashMap<>();

	// 父容器
	private ApplicationContext parent;

	private final Class<?> defaultConfigType;

	public NamedContextFactory(Class<?> defaultConfigType, String propertySourceName, String propertyName) {
		this(defaultConfigType, propertySourceName, propertyName, new HashMap<>());
	}

	public NamedContextFactory(Class<?> defaultConfigType, String propertySourceName, String propertyName, Map<String, ApplicationContextInitializer<GenericApplicationContext>> applicationContextInitializers) {
		this.defaultConfigType = defaultConfigType;
		this.propertySourceName = propertySourceName;
		this.propertyName = propertyName;
		this.applicationContextInitializers = applicationContextInitializers;
	}

	@Override
	public void setApplicationContext(ApplicationContext parent) throws BeansException {
		this.parent = parent;
	}

	public ApplicationContext getParent() {
		return parent;
	}

	public void setConfigurations(List<C> configurations) {
		for (C client : configurations) {
			this.configurations.put(client.getName(), client);
		}
	}

	public Set<String> getContextNames() {
		return new HashSet<>(this.contexts.keySet());
	}

	@Override
	public void destroy() {
		Collection<GenericApplicationContext> values = this.contexts.values();
		for (GenericApplicationContext context : values) {
			// This can fail, but it never throws an exception (you see stack traces
			// logged as WARN).
			context.close();
		}
		this.contexts.clear();
	}

	protected GenericApplicationContext getContext(String name) {
		if (!this.contexts.containsKey(name)) {
			synchronized (this.contexts) {
				if (!this.contexts.containsKey(name)) {
					this.contexts.put(name, createContext(name));
				}
			}
		}
		return this.contexts.get(name);
	}

	public GenericApplicationContext createContext(String name) {
		GenericApplicationContext context = buildContext(name);
		// there's an AOT initializer for this context
		if (applicationContextInitializers.get(name) != null) {
			applicationContextInitializers.get(name).initialize(context);
			context.refresh();
			return context;
		}
		registerBeans(name, context);
		context.refresh();
		return context;
	}

	public void registerBeans(String name, GenericApplicationContext context) {
		Assert.isInstanceOf(AnnotationConfigRegistry.class, context);
		AnnotationConfigRegistry registry = (AnnotationConfigRegistry) context;
		if (this.configurations.containsKey(name)) {
			for (Class<?> configuration : this.configurations.get(name).getConfiguration()) {
				registry.register(configuration);
			}
		}
		for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
			if (entry.getKey().startsWith("default.")) {
				for (Class<?> configuration : entry.getValue().getConfiguration()) {
					registry.register(configuration);
				}
			}
		}
		registry.register(PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType);
	}

	// 根据指定名称创建并配置一个 GenericApplicationContext，并根据父上下文、AOT 支持等条件动态选择上下文实现。
	public GenericApplicationContext buildContext(String name) {
		// https://github.com/spring-cloud/spring-cloud-netflix/issues/3101
		// https://github.com/spring-cloud/spring-cloud-openfeign/issues/475
		ClassLoader classLoader = getClass().getClassLoader();
		GenericApplicationContext context;
		if (this.parent != null) {
			DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
			if (parent instanceof ConfigurableApplicationContext) {
				beanFactory.setBeanClassLoader(((ConfigurableApplicationContext) parent).getBeanFactory().getBeanClassLoader());
			}
			else {
				beanFactory.setBeanClassLoader(classLoader);
			}
			
			context = AotDetector.useGeneratedArtifacts() ? new GenericApplicationContext(beanFactory) : new AnnotationConfigApplicationContext(beanFactory);
		}
		else {
			context = AotDetector.useGeneratedArtifacts() ? new GenericApplicationContext() : new AnnotationConfigApplicationContext();
		}
		context.setClassLoader(classLoader);
		context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(this.propertySourceName, Collections.singletonMap(this.propertyName, name)));
		if (this.parent != null) {
			// Uses Environment from parent as well as beans
			context.setParent(this.parent);
		}
		context.setDisplayName(generateDisplayName(name));
		return context;
	}

	protected String generateDisplayName(String name) {
		return this.getClass().getSimpleName() + "-" + name;
	}

	public <T> T getInstance(String name, Class<T> type) {
		GenericApplicationContext context = getContext(name);
		try {
			return context.getBean(type);
		}
		catch (NoSuchBeanDefinitionException e) {
			// ignore
		}
		return null;
	}

	public <T> ObjectProvider<T> getLazyProvider(String name, Class<T> type) {
		return new ClientFactoryObjectProvider<>(this, name, type);
	}

	public <T> ObjectProvider<T> getProvider(String name, Class<T> type) {
		GenericApplicationContext context = getContext(name);
		return context.getBeanProvider(type);
	}

	public <T> T getInstance(String name, Class<?> clazz, Class<?>... generics) {
		ResolvableType type = ResolvableType.forClassWithGenerics(clazz, generics);
		return getInstance(name, type);
	}

	@SuppressWarnings("unchecked")
	public <T> T getInstance(String name, ResolvableType type) {
		GenericApplicationContext context = getContext(name);
		String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context, type);
		for (String beanName : beanNames) {
			if (context.isTypeMatch(beanName, type)) {
				return (T) context.getBean(beanName);
			}
		}
		return null;
	}

	@SuppressWarnings("unchecked")
	public <T> T getAnnotatedInstance(String name, ResolvableType type, Class<? extends Annotation> annotationType) {
		GenericApplicationContext context = getContext(name);
		String[] beanNames = BeanFactoryUtils.beanNamesForAnnotationIncludingAncestors(context, annotationType);

		List<T> beans = new ArrayList<>();
		for (String beanName : beanNames) {
			if (context.isTypeMatch(beanName, type)) {
				beans.add((T) context.getBean(beanName));
			}
		}
		if (beans.size() > 1) {
			throw new IllegalStateException("Only one annotated bean for type expected.");
		}
		return beans.isEmpty() ? null : beans.get(0);
	}

	public <T> Map<String, T> getInstances(String name, Class<T> type) {
		GenericApplicationContext context = getContext(name);

		return BeanFactoryUtils.beansOfTypeIncludingAncestors(context, type);
	}

	public Map<String, C> getConfigurations() {
		return configurations;
	}

	/**
	 * Specification with name and configuration.
	 */
	public interface Specification {

		String getName();

		Class<?>[] getConfiguration();

	}

}

ClientFactoryObjectProvider

ClientFactoryObjectProvider 是一个特殊的 ObjectProvider，它通过延迟解析实际的 ObjectProvider，以便在创建命名的子上下文后再解析对象。

class ClientFactoryObjectProvider<T> implements ObjectProvider<T> {

	private final NamedContextFactory<?> clientFactory;

	private final String name;

	private final Class<T> type;

	private ObjectProvider<T> provider;

	ClientFactoryObjectProvider(NamedContextFactory<?> clientFactory, String name, Class<T> type) {
		this.clientFactory = clientFactory;
		this.name = name;
		this.type = type;
	}

	@Override
	public T getObject(Object... args) throws BeansException {
		return delegate().getObject(args);
	}

	@Override
	@Nullable
	public T getIfAvailable() throws BeansException {
		return delegate().getIfAvailable();
	}

	@Override
	public T getIfAvailable(Supplier<T> defaultSupplier) throws BeansException {
		return delegate().getIfAvailable(defaultSupplier);
	}

	@Override
	public void ifAvailable(Consumer<T> dependencyConsumer) throws BeansException {
		delegate().ifAvailable(dependencyConsumer);
	}

	@Override
	@Nullable
	public T getIfUnique() throws BeansException {
		return delegate().getIfUnique();
	}

	@Override
	public T getIfUnique(Supplier<T> defaultSupplier) throws BeansException {
		return delegate().getIfUnique(defaultSupplier);
	}

	@Override
	public void ifUnique(Consumer<T> dependencyConsumer) throws BeansException {
		delegate().ifUnique(dependencyConsumer);
	}

	@Override
	public Iterator<T> iterator() {
		return delegate().iterator();
	}

	@Override
	public Stream<T> stream() {
		return delegate().stream();
	}

	@Override
	public T getObject() throws BeansException {
		return delegate().getObject();
	}

	@Override
	public void forEach(Consumer<? super T> action) {
		delegate().forEach(action);
	}

	@Override
	public Spliterator<T> spliterator() {
		return delegate().spliterator();
	}

	private ObjectProvider<T> delegate() {
		if (this.provider == null) {
			this.provider = this.clientFactory.getProvider(this.name, this.type);
		}
		return this.provider;
	}

}

实现

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