java集合框架中包含哪些接口和类，Spring按类型自动装配注入数组、集合、Map

Spring按类型自动装配注入数组、集合、Map时，是把应用上下文中对应类型的bean装配进集合，而不是直接查找一个对应类型的集合然后注入。以下面这段代码为例：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import java.util.*;@Component("cdPlayers")
public class CDPlayers {@Autowiredprivate MediaPlayer[] mediaPlayerArr;@Autowiredprivate List<MediaPlayer> mediaPlayerList;@Autowiredprivate Map<String, MediaPlayer> mediaPlayerMap;@Autowiredpublic void printInfo() {System.out.println(Arrays.toString(mediaPlayerArr));System.out.println(mediaPlayerList);System.out.println(mediaPlayerMap);}
}

Spring会查找应用上下文里可赋给MediaPlayer类型的bean放进mediaPlayerArr数组，查找可赋给MediaPlayer类型的bean放进mediaPlayerList，查找可赋给MediaPlayer类型的bean put进mediaPlayerMap，key为bean的name。

这个过程的源码在DefaultListableBeanFactory的doResolveDependency方法中，具体如下(Spring版本是5.0.2)：

	@Nullablepublic Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);try {Object shortcut = descriptor.resolveShortcut(this);if (shortcut != null) {return shortcut;}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;}Map<String, Object> 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) {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.Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();autowiredBeanName = entry.getKey();instanceCandidate = entry.getValue();}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);}}@Nullableprivate Object resolveMultipleBeans(DependencyDescriptor descriptor, @Nullable String beanName,@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) {Class<?> type = descriptor.getDependencyType();if (type.isArray()) {Class<?> componentType = type.getComponentType();ResolvableType resolvableType = descriptor.getResolvableType();Class<?> resolvedArrayType = resolvableType.resolve();if (resolvedArrayType != null && resolvedArrayType != type) {type = resolvedArrayType;componentType = resolvableType.getComponentType().resolve();}if (componentType == null) {return null;}Map<String, Object> matchingBeans = findAutowireCandidates(beanName, componentType,new MultiElementDescriptor(descriptor));if (matchingBeans.isEmpty()) {return null;}if (autowiredBeanNames != null) {autowiredBeanNames.addAll(matchingBeans.keySet());}TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());Object result = converter.convertIfNecessary(matchingBeans.values(), type);if (getDependencyComparator() != null && result instanceof Object[]) {Arrays.sort((Object[]) result, adaptDependencyComparator(matchingBeans));}return result;}else if (Collection.class.isAssignableFrom(type) && type.isInterface()) {Class<?> elementType = descriptor.getResolvableType().asCollection().resolveGeneric();if (elementType == null) {return null;}Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType,new MultiElementDescriptor(descriptor));if (matchingBeans.isEmpty()) {return null;}if (autowiredBeanNames != null) {autowiredBeanNames.addAll(matchingBeans.keySet());}TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());Object result = converter.convertIfNecessary(matchingBeans.values(), type);if (getDependencyComparator() != null && result instanceof List) {Collections.sort((List<?>) result, adaptDependencyComparator(matchingBeans));}return result;}else if (Map.class == type) {ResolvableType mapType = descriptor.getResolvableType().asMap();Class<?> keyType = mapType.resolveGeneric(0);if (String.class != keyType) {return null;}Class<?> valueType = mapType.resolveGeneric(1);if (valueType == null) {return null;}Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType,new MultiElementDescriptor(descriptor));if (matchingBeans.isEmpty()) {return null;}if (autowiredBeanNames != null) {autowiredBeanNames.addAll(matchingBeans.keySet());}return matchingBeans;}else {return null;}}

我们可以看到在resolveMultipleBeans方法中：

1. 如果是数组，则获取数组元素类型，查找匹配该类型的所有bean，返回一个这些bean的数组；
2. 如果该类可赋给Collection，并且是一个接口，则获取集合元素类型，查找匹配该类型的所有bean，返回一个这些bean的集合；
3. 如果该类型是Map(注意是type == Map.class)，且key是String类型，则获取Map的value的类型，查找匹配该类型的所有bean，这是一个key为bean name、value为bean实例的一个Map，返回这个Map。
4. 其他情况则是我们所熟知的按类型自动装配过程。