spring runtime 更新 bean

前一篇博客我们提到， 如果bean是prototype或者刷新重新create后， 读取还是旧的properties， 所以从根本来说, 我们需要更新BeanDefinition，如此才能保证在重新初始化Bean的时候使用最新的配置。

运行时动态注册 bean 到 spring 容器

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使用主要通过BeanDefinitionBuilder构建BeanDefinition, 然后通过DefaultListableBeanFactory.registerBeanDefinition注册到容器中:

BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(SomeClass.class);
builder.addPropertyReference("propertyName", "someBean");  // add dependency to other bean
builder.addPropertyValue("propertyName", someValue);      // set property value
DefaultListableBeanFactory factory = (DefaultListableBeanFactory) context.getBeanFactory();
factory.registerBeanDefinition("beanName", builder.getBeanDefinition());

registerBeanDefinition(String beanName, BeanDefinition beanDefinition) 的内部逻辑如下, 主要是验证BeanDefinition和清除缓存：

   @Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
		throws BeanDefinitionStoreException {

	Assert.hasText(beanName, "Bean name must not be empty");
	Assert.notNull(beanDefinition, "BeanDefinition must not be null");

	...

	BeanDefinition oldBeanDefinition;

       // beanDefinitionMap
	oldBeanDefinition = this.beanDefinitionMap.get(beanName);
	if (oldBeanDefinition != null) {
           // 是否允许 BeanDefinition 的 Overriding
		if (!isAllowBeanDefinitionOverriding()) {
			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
					"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
					"': There is already [" + oldBeanDefinition + "] bound.");
		}
		...
	}
	else {
		this.beanDefinitionNames.add(beanName);
		this.manualSingletonNames.remove(beanName);
		this.frozenBeanDefinitionNames = null;
	}
	this.beanDefinitionMap.put(beanName, beanDefinition);

	if (oldBeanDefinition != null || containsSingleton(beanName)) {
           // 这里重置该 bean 的所有 definition caches, 包括派生于此bean的
		resetBeanDefinition(beanName);
	}
}

更新依赖这个动态 Bean 的 Bean

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注册之后, 如果使用singleton模式的话, 由于singleton实例和缓存并没有改变, 所以要进行更新DynamicBean.

方法1: destroySingleton

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这个方法简单粗暴, 使用 destroyXXX 可以销毁旧的Bean :

factory.destroySingleton("calculation");
factory.destroyBean();
factory.destroyXXX();

例如 org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#destroySingleton :

   public void destroySingleton(String beanName) {
	// Remove a registered singleton of the given name, if any.
	removeSingleton(beanName);

	// Destroy the corresponding DisposableBean instance.
	DisposableBean disposableBean;
	synchronized (this.disposableBeans) {
		disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
	}
	destroyBean(beanName, disposableBean);
}


   protected void destroyBean(String beanName, DisposableBean bean) {
	// Trigger destruction of dependent beans first...
	Set<String> dependencies = this.dependentBeanMap.remove(beanName);
	if (dependencies != null) {
		if (logger.isDebugEnabled()) {
			logger.debug("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
		}
		for (String dependentBeanName : dependencies) {
			destroySingleton(dependentBeanName);
		}
	}

	// Actually destroy the bean now...
	if (bean != null) {
		try {
			bean.destroy();
		}
		catch (Throwable ex) {
			logger.error("Destroy method on bean with name '" + beanName + "' threw an exception", ex);
		}
	}

	// Trigger destruction of contained beans...
	Set<String> containedBeans = this.containedBeanMap.remove(beanName);
	if (containedBeans != null) {
		for (String containedBeanName : containedBeans) {
			destroySingleton(containedBeanName);
		}
	}

	// Remove destroyed bean from other beans' dependencies.
	synchronized (this.dependentBeanMap) {
		for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
			Map.Entry<String, Set<String>> entry = it.next();
			Set<String> dependenciesToClean = entry.getValue();
			dependenciesToClean.remove(beanName);
			if (dependenciesToClean.isEmpty()) {
				it.remove();
			}
		}
	}

	// Remove destroyed bean's prepared dependency information.
	this.dependenciesForBeanMap.remove(beanName);
}

如上, 内部的singletonObjects singletonFactories earlySingletonObjects registeredSingletons containedBeans containedBeanMap等记录会清除掉这个Bean.

当下次需要这个Bean的时候, 如下面 org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean 代码所示, 如果没有缓存, 就会重新创建这个Bean.

protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {

		final String beanName = transformedBeanName(name);
		Object bean;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			if (logger.isDebugEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
			}

			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			try {
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dependsOnBean : dependsOn) {
						if (isDependent(beanName, dependsOnBean)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
						}
						registerDependentBean(dependsOnBean, beanName);
						getBean(dependsOnBean);
					}
				}

				// Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
						@Override
						public Object getObject() throws BeansException {
							try {
								return createBean(beanName, mbd, args);
							}
							catch (BeansException ex) {
								// Explicitly remove instance from singleton cache: It might have been put there
								// eagerly by the creation process, to allow for circular reference resolution.
								// Also remove any beans that received a temporary reference to the bean.
								destroySingleton(beanName);
								throw ex;
							}
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					final Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
							@Override
							public Object getObject() throws BeansException {
								beforePrototypeCreation(beanName);
								try {
									return createBean(beanName, mbd, args);
								}
								finally {
									afterPrototypeCreation(beanName);
								}
							}
						});
						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new BeanCreationException(beanName,
								"Scope '" + scopeName + "' is not active for the current thread; " +
								"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
								ex);
					}
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
			try {
				return getTypeConverter().convertIfNecessary(bean, requiredType);
			}
			catch (TypeMismatchException ex) {
				if (logger.isDebugEnabled()) {
					logger.debug("Failed to convert bean '" + name + "' to required type [" +
							ClassUtils.getQualifiedName(requiredType) + "]", ex);
				}
				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
			}
		}
		return (T) bean;
	}

从上可知, 因为已经destroy了DynamicBean, 所以Object sharedInstance = getSingleton(beanName) 是null的, 所以需要重新缓存DynamicBean, org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean 被调用, 这样我们的修改就被刷新了.

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
		Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isDebugEnabled()) {
				logger.debug("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			addSingletonFactory(beanName, new ObjectFactory<Object>() {
				@Override
				public Object getObject() throws BeansException {
					return getEarlyBeanReference(beanName, mbd, bean);
				}
			});
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				throw (BeanCreationException) ex;
			}
			else {
				throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
			}
		}

		if (earlySingletonExposure) {
			Object earlySingletonReference = getSingleton(beanName, false);
			if (earlySingletonReference != null) {
				if (exposedObject == bean) {
					exposedObject = earlySingletonReference;
				}
				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
					String[] dependentBeans = getDependentBeans(beanName);
					Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
					for (String dependentBean : dependentBeans) {
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
							actualDependentBeans.add(dependentBean);
						}
					}
					if (!actualDependentBeans.isEmpty()) {
						throw new BeanCurrentlyInCreationException(beanName,
								"Bean with name '" + beanName + "' has been injected into other beans [" +
								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
								"] in its raw version as part of a circular reference, but has eventually been " +
								"wrapped. This means that said other beans do not use the final version of the " +
								"bean. This is often the result of over-eager type matching - consider using " +
								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
					}
				}
			}
		}

		// Register bean as disposable.
		try {
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	}

方法2: WrapBean

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• 一个比较好的策略是定义一个 WrapBean 包一下这个可能在runtime被动态更新的 DynamicBean, 大概如下:

public class WrapBean {

    @Resource
    DynamicBean dynamicBean;

    // get set...
}

这样的话, 动态修改后只需要更新这个WrapBean的dynamicBean, 而且对系统的影响相对较小.

参考

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http://stackoverflow.com/questions/15328904/dynamically-declare-beans-at-runtime-in-spring
http://stackoverflow.com/questions/12800769/replace-spring-bean-in-one-context-with-mock-version-from-another-context
http://stackoverflow.com/questions/11606504/registering-beansprototype-at-runtime-in-spring
http://stackoverflow.com/questions/8711560/dynamic-creation-of-beans-in-spring
http://shayanth.blogspot.com/2009/10/dynamic-bean-creation-in-spring.html
http://stackoverflow.com/questions/4540713/add-bean-programatically-to-spring-web-app-context
http://stackoverflow.com/questions/27998502/java-spring-recreate-specific-bean