Spring 注入集合类型

定义了一个类： 

@Service
public class StringTest implements CachedRowSet,SortedSet<String>,Cloneable

@Controller
public class HomeController {
@Autowired
CachedRowSet message;

@Autowired
CachedRowSet message1;
}

 这里CachedRowSet ， 等其他接口都是可以注入的，包括StringTest  也行。 
但是使用： 

@Autowired
SortedSet<String> message

 就不行了。启动报错。 

源码分析：

org.springframework.beans.factory.support.DefaultListableBeanFactory

protected Object doResolveDependency(DependencyDescriptor descriptor, Class<?> type, String beanName,
        Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {

    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()));
    }

    if (type.isArray()) {
        Class<?> componentType = type.getComponentType();
        Map<String, Object> matchingBeans = findAutowireCandidates(beanName, componentType, descriptor);
        if (matchingBeans.isEmpty()) {
            if (descriptor.isRequired()) {
                raiseNoSuchBeanDefinitionException(componentType, "array of " + componentType.getName(), descriptor);
            }
            return null;
        }
        if (autowiredBeanNames != null) {
            autowiredBeanNames.addAll(matchingBeans.keySet());
        }
        TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
        return converter.convertIfNecessary(matchingBeans.values(), type);
    }
    else if (Collection.class.isAssignableFrom(type) && type.isInterface()) {
        Class<?> elementType = descriptor.getCollectionType();
        if (elementType == null) {
            if (descriptor.isRequired()) {
                throw new FatalBeanException("No element type declared for collection [" + type.getName() + "]");
            }
            return null;
        }
        Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType, descriptor);
        if (matchingBeans.isEmpty()) {
            if (descriptor.isRequired()) {
                raiseNoSuchBeanDefinitionException(elementType, "collection of " + elementType.getName(), descriptor);
            }
            return null;
        }
        if (autowiredBeanNames != null) {
            autowiredBeanNames.addAll(matchingBeans.keySet());
        }
        TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
        return converter.convertIfNecessary(matchingBeans.values(), type);
    }
    else if (Map.class.isAssignableFrom(type) && type.isInterface()) {
        Class<?> keyType = descriptor.getMapKeyType();
        if (keyType == null || !String.class.isAssignableFrom(keyType)) {
            if (descriptor.isRequired()) {
                throw new FatalBeanException("Key type [" + keyType + "] of map [" + type.getName() +
                        "] must be assignable to [java.lang.String]");
            }
            return null;
        }
        Class<?> valueType = descriptor.getMapValueType();
        if (valueType == null) {
            if (descriptor.isRequired()) {
                throw new FatalBeanException("No value type declared for map [" + type.getName() + "]");
            }
            return null;
        }
        Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType, descriptor);
        if (matchingBeans.isEmpty()) {
            if (descriptor.isRequired()) {
                raiseNoSuchBeanDefinitionException(valueType, "map with value type " + valueType.getName(), descriptor);
            }
            return null;
        }
        if (autowiredBeanNames != null) {
            autowiredBeanNames.addAll(matchingBeans.keySet());
        }
        return matchingBeans;
    }
    else {
        Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
        if (matchingBeans.isEmpty()) {
            if (descriptor.isRequired()) {
                raiseNoSuchBeanDefinitionException(type, "", descriptor);
            }
            return null;
        }
        if (matchingBeans.size() > 1) {
            String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor);
            if (primaryBeanName == null) {
                throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
            }
            if (autowiredBeanNames != null) {
                autowiredBeanNames.add(primaryBeanName);
            }
            return matchingBeans.get(primaryBeanName);
        }
        // We have exactly one match.
        Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
        if (autowiredBeanNames != null) {
            autowiredBeanNames.add(entry.getKey());
        }
        return entry.getValue();
    }
}

从上边的源码大家可以看出：

1、首先判断注入的类型，如果是数组、Collection、Map，则注入的是元素数据，即查找与元素类型相同的Bean的注入到集合，而不是找跟集合类型相同的

2、对于Map，key只能是String类型，而且默认是Bean的名字

结论：

1、对于数组、集合、Map，注入的元素类型，如SortedSet<String> 其实是找所有String类型的Bean注入到集合

2、Map，key只能是String类型，而且默认是Bean的名字