Spring自动注入的应用
这篇文章主要讲解了“Spring自动注入的应用”,文中的讲解内容简单清晰,易于学习与理解,下面请大家跟着小编的思路慢慢深入,一起来研究和学习“Spring自动注入的应用”吧!
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自动装配
@Nullable public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName, @Nullable SetautowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException { InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor); try { Object shortcut = descriptor.resolveShortcut(this); if (shortcut != null) { return shortcut; } // class com.ypf.ServiceB Class> type = descriptor.getDependencyType(); Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor); if (value != null) { if (value instanceof String) { String strVal = resolveEmbeddedValue((String) value); BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null); value = evaluateBeanDefinitionString(strVal, bd); } TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter()); return (descriptor.getField() != null ? converter.convertIfNecessary(value, type, descriptor.getField()) : converter.convertIfNecessary(value, type, descriptor.getMethodParameter())); } Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter); if (multipleBeans != null) { return multipleBeans; } // 关键点 !!! 去 spring ioc 容器中找到需要注入的 type 类型的 bean Map matchingBeans = findAutowireCandidates(beanName, type, descriptor); if (matchingBeans.isEmpty()) { if (isRequired(descriptor)) { raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor); } return null; } String autowiredBeanName; Object instanceCandidate; if (matchingBeans.size() > 1) { // Determine the autowire candidate in the given set of beans. // Looks for {@code @Primary} and {@code @Priority} (in that order). autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor); if (autowiredBeanName == null) { if (isRequired(descriptor) || !indicatesMultipleBeans(type)) { return descriptor.resolveNotUnique(type, matchingBeans); } else { // In case of an optional Collection/Map, silently ignore a non-unique case: // possibly it was meant to be an empty collection of multiple regular beans // (before 4.3 in particular when we didn't even look for collection beans). return null; } } instanceCandidate = matchingBeans.get(autowiredBeanName); } else { // We have exactly one match. // 将得到的 bean 从 matchingBeans 这个 map 中取出来。 Map.Entry entry = matchingBeans.entrySet().iterator().next(); autowiredBeanName = entry.getKey(); instanceCandidate = entry.getValue(); } // 为什么要加入 成功注入 beanName 放到一个 Set 集合中 if (autowiredBeanNames != null) { autowiredBeanNames.add(autowiredBeanName); } // ??? if (instanceCandidate instanceof Class) { instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this); } Object result = instanceCandidate; if (result instanceof NullBean) { if (isRequired(descriptor)) { raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor); } result = null; } if (!ClassUtils.isAssignableValue(type, result)) { throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass()); } return result; } finally { ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint); } }
DependencyDescriptor
依赖描述器,大概描述了 XXX 里的 field 需要自动装配 xxx 类型的 bean。
descriptor.resolveCandidate 里面实际上就是调用了 getBean
findAutowireCandidates
根据一些规则找到一些 candidateNames,把这些 candidateName,beanInstance 放到 map 中返回。 beanInstance 是根据调用 getBean(candidateName) 得到的。
protected MapfindAutowireCandidates( @Nullable String beanName, Class> requiredType, DependencyDescriptor descriptor) { // 先根据自动装配的 Class 类型去找到 spring ioc 容器中的所有是这种类型的 bean 的 name。 // Ancestors 祖先 String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors( this, requiredType, true, descriptor.isEager()); Map result = new LinkedHashMap<>(candidateNames.length); // 解析过的依赖会被缓存起来,根据 requiredType 去看缓存中没有有,有的话直接取出来 for (Class> autowiringType : this.resolvableDependencies.keySet()) { if (autowiringType.isAssignableFrom(requiredType)) { Object autowiringValue = this.resolvableDependencies.get(autowiringType); autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType); if (requiredType.isInstance(autowiringValue)) { result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue); break; } } } for (String candidate : candidateNames) { // 如果自动装配的属性的类型不是这个类,且是自动装配的候选就加入到 result。按 byType if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) { addCandidateEntry(result, candidate, descriptor, requiredType); } } if (result.isEmpty() && !indicatesMultipleBeans(requiredType)) { // Consider fallback matches if the first pass failed to find anything... DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch(); for (String candidate : candidateNames) { // 如果自动装配的属性的类型不是这个类,且是自动装配的候选就加入到 result。按 byName 去找。 if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor)) { addCandidateEntry(result, candidate, descriptor, requiredType); } } if (result.isEmpty()) { // Consider self references as a final pass... // but in the case of a dependency collection, not the very same bean itself. for (String candidate : candidateNames) { if (isSelfReference(beanName, candidate) && (!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) && isAutowireCandidate(candidate, fallbackDescriptor)) { addCandidateEntry(result, candidate, descriptor, requiredType); } } } } return result; }
???
isAutowireCandidate
先按 byType 去找,然后去按 byName 去找?
protected boolean isAutowireCandidate(String beanName, DependencyDescriptor descriptor, AutowireCandidateResolver resolver) throws NoSuchBeanDefinitionException { String beanDefinitionName = BeanFactoryUtils.transformedBeanName(beanName); if (containsBeanDefinition(beanDefinitionName)) { return isAutowireCandidate(beanName, getMergedLocalBeanDefinition(beanDefinitionName), descriptor, resolver); } else if (containsSingleton(beanName)) { return isAutowireCandidate(beanName, new RootBeanDefinition(getType(beanName)), descriptor, resolver); } BeanFactory parent = getParentBeanFactory(); if (parent instanceof DefaultListableBeanFactory) { // No bean definition found in this factory -> delegate to parent. return ((DefaultListableBeanFactory) parent).isAutowireCandidate(beanName, descriptor, resolver); } else if (parent instanceof ConfigurableListableBeanFactory) { // If no DefaultListableBeanFactory, can't pass the resolver along. return ((ConfigurableListableBeanFactory) parent).isAutowireCandidate(beanName, descriptor); } else { return true; } }
感谢各位的阅读,以上就是“Spring自动注入的应用”的内容了,经过本文的学习后,相信大家对Spring自动注入的应用这一问题有了更深刻的体会,具体使用情况还需要大家实践验证。这里是创新互联,小编将为大家推送更多相关知识点的文章,欢迎关注!
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