詳解Spring支持的各種數據類型的注入，你都用過哪些？

作者：Springboot實戰案例錦集 2023-09-14 08:16:50

判斷是否有@Lazy注解，如果有該注解那么會創建代理對象，否則返回null，總結：如果注入的屬性有@Lazy注解，那么會返回由ProxyFactory對象創建的代理對象。

1 判斷類型

注入的屬性判斷其類型：

Optional
ObjectFactory
ObjectProvider
javax.inject.Provider

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
    private static Class<?> javaxInjectProviderClass;


    static {
        try {
            javaxInjectProviderClass =
                    ClassUtils.forName("javax.inject.Provider", DefaultListableBeanFactory.class.getClassLoader());
        } catch (ClassNotFoundException ex) {
            javaxInjectProviderClass = null;
        }
    }
    public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
            @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
        if (Optional.class == descriptor.getDependencyType()) {
            return createOptionalDependency(descriptor, requestingBeanName);
        } else if (ObjectFactory.class == descriptor.getDependencyType() ||
                ObjectProvider.class == descriptor.getDependencyType()) {
            return new DependencyObjectProvider(descriptor, requestingBeanName);
        } else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
            return new Jsr330Factory().createDependencyProvider(descriptor, requestingBeanName);
        } else {
            // 判斷是否有@Lazy注解，如果有該注解那么會創建代理對象，否則返回null
            // 總結：如果注入的屬性有@Lazy注解，那么會返回由ProxyFactory對象創建的代理對象
            Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(descriptor, requestingBeanName);
            if (result == null) {
                // 解析查找依賴注入的對象
                result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
            }
            return result;
        }
    }
}

2 查找依賴對象

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
  public 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();


      // 判斷需要注入的類型是否是一個集合（如何：List<Users> beans）
      // 2.1 
      Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
      if (multipleBeans != null) {
          return multipleBeans;
      }
      // 查找與所需類型匹配的bean實例
      // 2.2
      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;


      // 如果找到多個
      if (matchingBeans.size() > 1) {
          // 在這里會判斷多個Bean中是否有一個@Primary注解的Bean
          // 如果沒有@Primary，繼續獲取是否有@Priority（優先級）注解
          // 如果沒有則返回null，如果有則返回值越小的優先級越高（如果有多個優先級一樣，則系統報錯）
          // 如果上面都返回的null，那么最后會通過beanName進行匹配
          autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
          if (autowiredBeanName == null) {
              if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
                  // 如果是必須的 或者 不是集合類型的Bean注入；那么這里拋出異常
                  return descriptor.resolveNotUnique(descriptor.getResolvableType(), matchingBeans);
              } else {
                  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);
    }
  }
}

2.1 判斷集合類型

判斷需要注入的屬性的數據類型是否是如下幾種。

StreamDependencyDescriptor
Array
Collection
Map

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
  private Object resolveMultipleBeans(DependencyDescriptor descriptor, @Nullable String beanName,
          @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) {


    Class<?> type = descriptor.getDependencyType();


    if (descriptor instanceof StreamDependencyDescriptor) {
      Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
      if (autowiredBeanNames != null) {
        autowiredBeanNames.addAll(matchingBeans.keySet());
      }
      Stream<Object> stream = matchingBeans.keySet().stream()
              .map(name -> descriptor.resolveCandidate(name, type, this))
              .filter(bean -> !(bean instanceof NullBean));
      if (((StreamDependencyDescriptor) descriptor).isOrdered()) {
        stream = stream.sorted(adaptOrderComparator(matchingBeans));
      }
      return stream;
    } else if (type.isArray()) {
      Class<?> componentType = type.getComponentType();
      ResolvableType resolvableType = descriptor.getResolvableType();
      Class<?> resolvedArrayType = resolvableType.resolve(type);
      if (resolvedArrayType != type) {
        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(), resolvedArrayType);
      if (result instanceof Object[]) {
        Comparator<Object> comparator = adaptDependencyComparator(matchingBeans);
        if (comparator != null) {
          Arrays.sort((Object[]) result, comparator);
        }
      }
      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 (result instanceof List) {
        if (((List<?>) result).size() > 1) {
          Comparator<Object> comparator = adaptDependencyComparator(matchingBeans);
          if (comparator != null) {
              ((List<?>) result).sort(comparator);
          }
        }
      }
      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;
    }
  }
}

2.2 查找Bean

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
  protected Map<String, Object> findAutowireCandidates(
          @Nullable String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
    // 通過類型獲取指定類型的Bean
    String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
            this, requiredType, true, descriptor.isEager());
    Map<String, Object> result = CollectionUtils.newLinkedHashMap(candidateNames.length);
    // resolvableDependencies 集合中保存了，容器內置的和自定義注冊的依賴注入對象
    //（如：HttpServletRequest對象的注入為該集合內部指定的對象）
    for (Map.Entry<Class<?>, Object> classObjectEntry : this.resolvableDependencies.entrySet()) {
        Class<?> autowiringType = classObjectEntry.getKey();
      if (autowiringType.isAssignableFrom(requiredType)) {
        Object autowiringValue = classObjectEntry.getValue();
        autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
        if (requiredType.isInstance(autowiringValue)) {
          result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
          break;
        }
      }
    }
    for (String candidate : candidateNames) {
      // 判斷是否自己引用自己
      if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {
        addCandidateEntry(result, candidate, descriptor, requiredType);
      }
    }
    if (result.isEmpty()) {
      boolean multiple = indicatesMultipleBeans(requiredType);
      // Consider fallback matches if the first pass failed to find anything...
      DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
      for (String candidate : candidateNames) {
        if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor) &&
                (!multiple || getAutowireCandidateResolver().hasQualifier(descriptor))) {
          addCandidateEntry(result, candidate, descriptor, requiredType);
        }
      }
      if (result.isEmpty() && !multiple) {
        // 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;
  }
}

以上就是Spring在注入屬性的時候會判斷是什么數據類型進行相應的操作

完畢！！！

責任編輯：武曉燕來源： Spring全家桶實戰案例源碼

Lazy 注解 null