当初在配置类外面创立一个bean date
@Configurationpublic class DateConfig { @Bean("date") public Date date(){ return new Date(); }}工夫并不是变化无穷的，我想要获取以后工夫呢，应该怎么笼罩曾经在容器内bean。我一开始想到应用org..cloud.context.scope.refresh.RefreshScope,然而Spring boot我的项目并没有应用到Spring Cloud包，这个走不通，就试着registerBean动静注册雷同名字bean，想着能不能笼罩容器内bean，毕竟所谓容器只不过是Map而已，只有通过机制笼罩掉Map 上value 就能够实现动静刷新了。
private ApplicationContext applicationContext; @GetMapping("setting/now") public void dkd(){ GenericApplicationContext gac = (GenericApplicationContext)applicationContext; gac.registerBean("date",Date.class); }执行这个申请，间接报错了，抛出了一个BeanDefinitionOverrideException异样，bean不能被笼罩。在DefaultListableBeanFactory.registerBeanDefinition能够看到其中起因
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { // 省略多余代码 BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName); if (existingDefinition != null) { //对于曾经存在bean if (!isAllowBeanDefinitionOverriding()) { //如果allowBeanDefinitionOverriding 这个值为false 这里就会抛出异样 throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition); } else if (existingDefinition.getRole() < beanDefinition.getRole()) { //这里是BeanDefinition // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE if (logger.isInfoEnabled()) { logger.info("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } else if (!beanDefinition.equals(existingDefinition)) { if (logger.isDebugEnabled()) { logger.debug("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } else { if (logger.isTraceEnabled()) { logger.trace("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } this.beanDefinitionMap.put(beanName, beanDefinition); } //省略。。而后发现这个allowBeanDefinitionOverriding 在SpringBoot 刚初始化时，在SpringApplication 会初始化这个值，在SpringApplication.prepareContext
private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { context.setEnvironment(environment); postProcessApplicationContext(context); applyInitializers(context); listeners.contextPrepared(context); bootstrapContext.close(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // Add boot specific singleton beans ConfigurableListableBeanFactory beanFactory = context.getBeanFactory(); beanFactory.registerSingleton("springApplicationArguments", applicationArguments); if (printedBanner != null) { beanFactory.registerSingleton("springBootBanner", printedBanner); } if (beanFactory instanceof AbstractAutowireCapableBeanFactory) { ((AbstractAutowireCapableBeanFactory) beanFactory).setAllowCircularReferences(this.allowCircularReferences); if (beanFactory instanceof DefaultListableBeanFactory) { ((DefaultListableBeanFactory) beanFactory) .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding); //设置到DefaultListableBeanFactory中 } } if (this.lazyInitialization) { //开启懒加载配置 context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor()); } context.addBeanFactoryPostProcessor(new PropertySourceOrderingBeanFactoryPostProcessor(context)); // Load the sources Set<Object> sources = getAllSources(); Assert.notEmpty(sources, "Sources must not be empty"); load(context, sources.toArray(new Object[0])); listeners.contextLoaded(context); }接着看下配置文件值如何设置到SpringApplication.allowBeanDefinitionOverriding
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) { // Create and configure the environment ConfigurableEnvironment environment = getOrCreateEnvironment(); configureEnvironment(environment, applicationArguments.getSourceArgs()); ConfigurationPropertySources.attach(environment); listeners.environmentPrepared(bootstrapContext, environment); DefaultPropertiesPropertySource.moveToEnd(environment); Assert.state(!environment.containsProperty("spring.main.environment-prefix"), "Environment prefix cannot be set via properties."); bindToSpringApplication(environment); //将配置环境bind到属性中 if (!this.isCustomEnvironment) { environment = convertEnvironment(environment); } ConfigurationPropertySources.attach(environment); return environment; } protected void bindToSpringApplication(ConfigurableEnvironment environment) { try { //将配置文件绑定到以后属性上 //看起来就有ConfigurationProperties 那味了 Binder.get(environment).bind("spring.main", Bindable.ofInstance(this)); } catch (Exception ex) {//略} }在application.properties 增加上面配置
spring.main.allow-bean-definition-overriding=true
重启后从新执行HTTP 申请，没有报错了，从新获取date 这个bean，工夫也变成最新值了。
心得
增加多这一个配置预计为了兼容不同组件间可能存在一些bean 抵触状况，前面初始化bean组件能够笼罩Spring 外部曾经创立组件。如果当初Spring 外部曾经初始化bean A，并且胜利退出到容器中了，这时加载再加载Spring 组件也有一个Class 继承bean A，这是须要增加到容器中。如果没有beanName 雷同笼罩的机制，组件在初始化就会失败。
还有一点值得注意的，registerBean 这个办法只有在容器中删除这个bean 缓存，如何曾经将bean注入到对象属性中，这时这个值不会变动的，须要手动调用beanFactory.getBean("beanName")，因为只有这个bean不存在时候才会执行初始化。如果有这种bean刷新场景能够应用@Lookup来生成一个代理办法。
@Lookup public Date initDate() { //这里会将容器内Date类型注入，每次调用办法，从新从容器获取一次 return null; }