AutowireCandidateResolver：
Strategy interface for determining whether a specific bean definition qualifies as an autowire candidate for a specific dependency.
策略接口，对特定的依赖，这个接口决定一个特定的bean definition是否满足作为自动绑定的备选项
// 本接口Spring2.5就提供了 public interface AutowireCandidateResolver { default boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) { return bdHolder.getBeanDefinition().isAutowireCandidate(); } // Spring5.0后提供 default boolean isRequired(DependencyDescriptor descriptor) { return descriptor.isRequired(); } // 3.0后提供 @Nullable default Object getSuggestedValue(DependencyDescriptor descriptor) { return null; } // 4.0后提供 @Nullable default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, @Nullable String beanName) { return null; } }
继承关系如下：
SimpleAutowireCandidateResolver没有任何实现，就是一个Adapter
GenericTypeAwareAutowireCandidateResolver：基础实现，有核心逻辑方法：checkGenericTypeMatch(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor)，
作用为：根据给定的候选bean定义，将给定的依赖类型与其泛型类型信息匹配。（这就是泛型依赖注入的核心匹配逻辑，所以这列其实也是Spring4.0后才推出来的）
protected boolean checkGenericTypeMatch(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) { ResolvableType dependencyType = descriptor.getResolvableType(); if (dependencyType.getType() instanceof Class) { // No generic type -> we know it's a Class type-match, so no need to check again. return true; } ResolvableType targetType = null; boolean cacheType = false; RootBeanDefinition rbd = null; if (bdHolder.getBeanDefinition() instanceof RootBeanDefinition) { rbd = (RootBeanDefinition) bdHolder.getBeanDefinition(); } if (rbd != null) { targetType = rbd.targetType; if (targetType == null) { cacheType = true; // First, check factory method return type, if applicable targetType = getReturnTypeForFactoryMethod(rbd, descriptor); if (targetType == null) { RootBeanDefinition dbd = getResolvedDecoratedDefinition(rbd); if (dbd != null) { targetType = dbd.targetType; if (targetType == null) { targetType = getReturnTypeForFactoryMethod(dbd, descriptor); } } } } } if (targetType == null) { // Regular case: straight bean instance, with BeanFactory available. if (this.beanFactory != null) { Class<?> beanType = this.beanFactory.getType(bdHolder.getBeanName()); if (beanType != null) { targetType = ResolvableType.forClass(ClassUtils.getUserClass(beanType)); } } // Fallback: no BeanFactory set, or no type resolvable through it // -> best-effort match against the target class if applicable. if (targetType == null && rbd != null && rbd.hasBeanClass() && rbd.getFactoryMethodName() == null) { Class<?> beanClass = rbd.getBeanClass(); if (!FactoryBean.class.isAssignableFrom(beanClass)) { targetType = ResolvableType.forClass(ClassUtils.getUserClass(beanClass)); } } } if (targetType == null) { return true; } if (cacheType) { rbd.targetType = targetType; } if (descriptor.fallbackMatchAllowed() && targetType.hasUnresolvableGenerics()) { return true; } // Full check for complex generic type match... return dependencyType.isAssignableFrom(targetType); } @Nullable protected RootBeanDefinition getResolvedDecoratedDefinition(RootBeanDefinition rbd) { BeanDefinitionHolder decDef = rbd.getDecoratedDefinition(); if (decDef != null && this.beanFactory instanceof ConfigurableListableBeanFactory) { ConfigurableListableBeanFactory clbf = (ConfigurableListableBeanFactory) this.beanFactory; if (clbf.containsBeanDefinition(decDef.getBeanName())) { BeanDefinition dbd = clbf.getMergedBeanDefinition(decDef.getBeanName()); if (dbd instanceof RootBeanDefinition) { return (RootBeanDefinition) dbd; } } } return null; } @Nullable protected ResolvableType getReturnTypeForFactoryMethod(RootBeanDefinition rbd, DependencyDescriptor descriptor) { // Should typically be set for any kind of factory method, since the BeanFactory // pre-resolves them before reaching out to the AutowireCandidateResolver... ResolvableType returnType = rbd.factoryMethodReturnType; if (returnType == null) { Method factoryMethod = rbd.getResolvedFactoryMethod(); if (factoryMethod != null) { returnType = ResolvableType.forMethodReturnType(factoryMethod); } } if (returnType != null) { Class<?> resolvedClass = returnType.resolve(); if (resolvedClass != null && descriptor.getDependencyType().isAssignableFrom(resolvedClass)) { // Only use factory method metadata if the return type is actually expressive enough // for our dependency. Otherwise, the returned instance type may have matched instead // in case of a singleton instance having been registered with the container already. return returnType; } } return null; }
QualifierAnnotationAutowireCandidateResolver：对@Qualifier的解析，功能是将qualifier注解要自动绑定的field或者参数和bean definition qualifier相匹配。同时也支持通过@value注解来绑定表达式的值。另外还支持JSR-330的javax.inject.Qualifier注解
ContextAnnotationAutowireCandidateResolver：对@Lazy的解析
@Required：依赖检查；@Autowired：自动装配（可完全代替基于xml的装配）
@Value(value = “SpEL表达式”) 或者 @Value(value = “#{message}”)
@Qualifier：限定描述符，用于细粒度选择候选者
@Inject：等价于默认的@Autowired，只是没有required属性（支持@Primary）
QualifierAnnotationAutowireCandidateResolver#getSuggestedValue：处理标注了@Value注解的情况
private Class<? extends Annotation> valueAnnotationType = Value.class; // 拿到value注解的这个属性（若标注有@Value注解的话） @Override @Nullable public Object getSuggestedValue(DependencyDescriptor descriptor) { Object value = findValue(descriptor.getAnnotations()); if (value == null) { // 看看方法有没有标注 MethodParameter methodParam = descriptor.getMethodParameter(); if (methodParam != null) { value = findValue(methodParam.getMethodAnnotations()); } } return value; } /** * Determine a suggested value from any of the given candidate annotations. */ @Nullable protected Object findValue(Annotation[] annotationsToSearch) { // 寻找到@Value注解的value属性值 AnnotationAttributes attr = AnnotatedElementUtils.getMergedAnnotationAttributes( AnnotatedElementUtils.forAnnotations(annotationsToSearch), this.valueAnnotationType); if (attr != null) { return extractValue(attr); } return null; } /** * Extract the value attribute from the given annotation. * @since 4.3 */ protected Object extractValue(AnnotationAttributes attr) { Object value = attr.get(AnnotationUtils.VALUE); if (value == null) { throw new IllegalStateException("Value annotation must have a value attribute"); } return value; }
