Spring bean name 怎么来的？

sping的生命周期大概是这样的（生命周期），当然这个看也是看了个寂寞，看不出BeanName是怎么来。下面且看我细细道来。

spring刷新容器的整个过程分为下面这若干步骤：

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
				...
                // 生成bean name 在这一大步骤里面
				invokeBeanFactoryPostProcessors(beanFactory);
				...
		}
	}

下面看一下函数调用栈：可以看到就是解析的时候生成bean name的

下面看一下具体方法：

@Override
	public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
		if (definition instanceof AnnotatedBeanDefinition) {
			String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition);
			if (StringUtils.hasText(beanName)) {
				// Explicit bean name found.
				return beanName;
			}
		}
		// Fallback: generate a unique default bean name.
		return buildDefaultBeanName(definition, registry);
	}

从代码可以看出来如果自己指定了bean name 就用指定的名字，如果没有指定就用默认的策略生成bean name

下面是获取获取指定的bean name

protected String determineBeanNameFromAnnotation(AnnotatedBeanDefinition annotatedDef) {
		AnnotationMetadata amd = annotatedDef.getMetadata();
		Set<String> types = amd.getAnnotationTypes();
		String beanName = null;
		for (String type : types) {
			AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(amd, type);
			if (attributes != null) {
				Set<String> metaTypes = this.metaAnnotationTypesCache.computeIfAbsent(type, key -> {
					Set<String> result = amd.getMetaAnnotationTypes(key);
					return (result.isEmpty() ? Collections.emptySet() : result);
				});
				if (isStereotypeWithNameValue(type, metaTypes, attributes)) {
					Object value = attributes.get("value");
					if (value instanceof String) {
						String strVal = (String) value;
						if (StringUtils.hasLength(strVal)) {
							if (beanName != null && !strVal.equals(beanName)) {
								throw new IllegalStateException("Stereotype annotations suggest inconsistent " +
										"component names: '" + beanName + "' versus '" + strVal + "'");
							}
							beanName = strVal;
						}
					}
				}
			}
		}
		return beanName;
	}

下面是默认的策略生成bean name:

protected String buildDefaultBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
		return buildDefaultBeanName(definition);
	}

继续往里面看：就是获取全限定类名，再获取类名进行处理

protected String buildDefaultBeanName(BeanDefinition definition) {
		String beanClassName = definition.getBeanClassName();
		Assert.state(beanClassName != null, "No bean class name set");
		String shortClassName = ClassUtils.getShortName(beanClassName);
		return Introspector.decapitalize(shortClassName);
	}

从下面的代码可以看出有两种情况：

如果类名的长度大于1，且前两个字母都是大写，那么bean name就是 类名，否则就是bean name 将类名首字母变小写

public static String decapitalize(String name) {
        if (name == null || name.length() == 0) {
            return name;
        }
        if (name.length() > 1 && Character.isUpperCase(name.charAt(1)) &&
                        Character.isUpperCase(name.charAt(0))){
            return name;
        }
        char[] chars = name.toCharArray();
        chars[0] = Character.toLowerCase(chars[0]);
        return new String(chars);
    }