spring boot @Value源码解析
时间:2019-11-14
本文章向大家介绍spring boot @Value源码解析,主要包括spring boot @Value源码解析使用实例、应用技巧、基本知识点总结和需要注意事项,具有一定的参考价值,需要的朋友可以参考一下。
Spring boot 的@Value只能用于bean中,在bean的实例化时,会给@Value的属性赋值:如下面的例子:
@SpringBootApplication @Slf4j public class DemoApplication { @Value(value = "${server.port}") private String config; public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); } }
下面的类显示了bean的实例化方法:org.springframework.context.support.AbstractApplicationContext
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // 实例化方法 Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
bean的具体实例过过程,就不在这里说了,具体可以看前面的文章Spring boot IOC源码解析.
这个方法中:org.springframework.beans.factory.annotation.InjectionMetadata#inject 会遍历bean中所有的成员:
public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable { Collection<InjectedElement> checkedElements = this.checkedElements; Collection<InjectedElement> elementsToIterate = (checkedElements != null ? checkedElements : this.injectedElements); if (!elementsToIterate.isEmpty()) { for (InjectedElement element : elementsToIterate) { if (logger.isTraceEnabled()) { logger.trace("Processing injected element of bean '" + beanName + "': " + element); } element.inject(target, beanName, pvs); } } }
最终解析的代码如下:org.springframework.core.env.PropertySourcesPropertyResolver#getProperty(java.lang.String, java.lang.Class<T>, boolean)
@Nullable protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) { if (this.propertySources != null) { for (PropertySource<?> propertySource : this.propertySources) { if (logger.isTraceEnabled()) { logger.trace("Searching for key '" + key + "' in PropertySource '" + propertySource.getName() + "'"); } Object value = propertySource.getProperty(key); if (value != null) { if (resolveNestedPlaceholders && value instanceof String) { value = resolveNestedPlaceholders((String) value); } logKeyFound(key, propertySource, value); return convertValueIfNecessary(value, targetValueType); } } } if (logger.isTraceEnabled()) { logger.trace("Could not find key '" + key + "' in any property source"); } return null; }
propertySource的内容,可以看上篇博客,里面记录了spring boot是如何读取配置文件信息的。
原文地址:https://www.cnblogs.com/hankuikui/p/11858475.html
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