DefaultListableBeanFactory

DefaultListableBeanFactory，继承了 AbstractAutowireCapableBeanFactory 及实现了 ConfigurableListableBeanFactory、BeanDefinitionRegistry 接口。

类结构

略

字段

// JSR-330 支持
private static Class<?> javaxInjectProviderClass;
// DefaultListableBeanFactory 引用的缓存
private static final Map<String, Reference<DefaultListableBeanFactory>> serializableFactories = new ConcurrentHashMap<>(8);
// 序列号 id
private String serializationId;
// 是否允许用相同的名称重新注册不同的定义
private boolean allowBeanDefinitionOverriding = true;
// 是否允许懒加载
private boolean allowEagerClassLoading = true;
// 依赖排序顺序
private Comparator<Object> dependencyComparator;
// 解析器，用于检查 bean 定义是否为自动装配候选
private AutowireCandidateResolver autowireCandidateResolver = new SimpleAutowireCandidateResolver();
// 依赖类型和自动注入值的映射
private final Map<Class<?>, Object> resolvableDependencies = new ConcurrentHashMap<>(16);
// BeanDefinition 和 beanName 的映射
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
// 依赖类型和单例、非单例 bean 的映射
private final Map<Class<?>, String[]> allBeanNamesByType = new ConcurrentHashMap<>(64);
// 依赖类型和单例 bean 的映射
private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<>(64);
// bean 定义名称列表，按注册顺序排列。private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
// 手动注册的单例，按注册顺序排列
private volatile Set<String> manualSingletonNames = new LinkedHashSet<>(16);
// 固定配置的缓存的 bean 定义名数组
private volatile String[] frozenBeanDefinitionNames;
// 是否可以缓存所有 bean 的 bean 定义元数据
private volatile boolean configurationFrozen = false;

方法解析

DefaultListableBeanFactory

构造方法

public DefaultListableBeanFactory() {super();
}
public DefaultListableBeanFactory(@Nullable BeanFactory parentBeanFactory) {super(parentBeanFactory);
}

setSerializationId

getSerializationId

序列号设置，同时设置到 serializableFactories 中。

public void setSerializationId(@Nullable String serializationId) {if (serializationId != null) {serializableFactories.put(serializationId, new WeakReference<>(this));
    }
    else if (this.serializationId != null) {serializableFactories.remove(this.serializationId);
    }
    this.serializationId = serializationId;
}
public String getSerializationId() {return this.serializationId;}

setAllowBeanDefinitionOverriding

isAllowBeanDefinitionOverriding

setAllowEagerClassLoading

isAllowEagerClassLoading

setDependencyComparator

getDependencyComparator

setAutowireCandidateResolver

getAutowireCandidateResolver

allowAliasOverriding

set、get 代码略

copyConfigurationFrom

复制其他配置信息

public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {super.copyConfigurationFrom(otherFactory);
    if (otherFactory instanceof DefaultListableBeanFactory) {DefaultListableBeanFactory otherListableFactory = (DefaultListableBeanFactory) otherFactory;
        this.allowBeanDefinitionOverriding = otherListableFactory.allowBeanDefinitionOverriding;
        this.allowEagerClassLoading = otherListableFactory.allowEagerClassLoading;
        this.dependencyComparator = otherListableFactory.dependencyComparator;
        // A clone of the AutowireCandidateResolver since it is potentially BeanFactoryAware...
        setAutowireCandidateResolver(BeanUtils.instantiateClass(getAutowireCandidateResolver().getClass()));
        // Make resolvable dependencies (e.g. ResourceLoader) available here as well...
        this.resolvableDependencies.putAll(otherListableFactory.resolvableDependencies);
    }
}

getBean

获取 bean

public <T> T getBean(Class<T> requiredType) throws BeansException {
    // 根据 class 类型获取 bean
    return getBean(requiredType, (Object[]) null);
}
public <T> T getBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {Object resolved = resolveBean(ResolvableType.forRawClass(requiredType), args, false);
    if (resolved == null) {throw new NoSuchBeanDefinitionException(requiredType);
    }
    return (T) resolved;
}

getBeanProvider

获取 bean 的提供者

public <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType) throws BeansException {return getBeanProvider(ResolvableType.forRawClass(requiredType));
}
public <T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType) {return new BeanObjectProvider<T>() {
        @Override
        public T getObject() throws BeansException {T resolved = resolveBean(requiredType, null, false);
            if (resolved == null) {throw new NoSuchBeanDefinitionException(requiredType);
            }
            return resolved;
        }
        @Override
        public T getObject(Object... args) throws BeansException {T resolved = resolveBean(requiredType, args, false);
            if (resolved == null) {throw new NoSuchBeanDefinitionException(requiredType);
            }
            return resolved;
        }
        @Override
        @Nullable
        public T getIfAvailable() throws BeansException {return resolveBean(requiredType, null, false);
        }
        @Override
        @Nullable
        public T getIfUnique() throws BeansException {return resolveBean(requiredType, null, true);
        }
        @Override
        public Stream<T> stream() {return Arrays.stream(getBeanNamesForTypedStream(requiredType))
                    .map(name -> (T) getBean(name))
                    .filter(bean -> !(bean instanceof NullBean));
        }
        @Override
        public Stream<T> orderedStream() {String[] beanNames = getBeanNamesForTypedStream(requiredType);
            Map<String, T> matchingBeans = new LinkedHashMap<>(beanNames.length);
            for (String beanName : beanNames) {Object beanInstance = getBean(beanName);
                if (!(beanInstance instanceof NullBean)) {matchingBeans.put(beanName, (T) beanInstance);
                }
            }
            Stream<T> stream = matchingBeans.values().stream();
            return stream.sorted(adaptOrderComparator(matchingBeans));
        }
    };
}

resolveBean

private <T> T resolveBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) {NamedBeanHolder<T> namedBean = resolveNamedBean(requiredType, args, nonUniqueAsNull);
    if (namedBean != null) {return namedBean.getBeanInstance();
    }
    BeanFactory parent = getParentBeanFactory();
    // 如果父类是 DefaultListableBeanFactory，调用父类的 resolveBean 方法
    if (parent instanceof DefaultListableBeanFactory) {return ((DefaultListableBeanFactory) parent).resolveBean(requiredType, args, nonUniqueAsNull);
    }
    else if (parent != null) {
        // 如果父类不是 DefaultListableBeanFactory，且不为空，获取父类的 bean 的提供者
        ObjectProvider<T> parentProvider = parent.getBeanProvider(requiredType);
        if (args != null) {
            // 有参构造
            return parentProvider.getObject(args);
        }
        else {
            // 无参构造，getIfAvailable：实际存在才返回一个实例，*   getIfUnique：有多个实例时，返回默认的实例（比如 primary）return (nonUniqueAsNull ? parentProvider.getIfUnique() : parentProvider.getIfAvailable());
        }
    }
    return null;
}

getBeanNamesForTypedStream

通过 ResolvableType 获取 bean 名称

private String[] getBeanNamesForTypedStream(ResolvableType requiredType) {return BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this, requiredType);
}

containsBeanDefinition

检查此 bean 工厂是否包含具有指定名称的 bean 定义。不考虑本工厂可能参与的任何层级

public boolean containsBeanDefinition(String beanName) {Assert.notNull(beanName, "Bean name must not be null");
    return this.beanDefinitionMap.containsKey(beanName);
}

getBeanDefinitionCount

获取 bean 定义的个数

public int getBeanDefinitionCount() {return this.beanDefinitionMap.size();
}

getBeanDefinitionNames

不考虑此工厂可能参与的任何层次结构，并且忽略通过 bean 定义以外的其他方式注册的任何单例 bean

public String[] getBeanDefinitionNames() {String[] frozenNames = this.frozenBeanDefinitionNames;
    if (frozenNames != null) {return frozenNames.clone();
    }
    else {return StringUtils.toStringArray(this.beanDefinitionNames);
    }
}

getBeanNamesForType

根据 bean 定义或 factorybean 中 getObjectType 的值判断，返回与给定类型 (包括子类) 匹配的 bean 的名称。

public String[] getBeanNamesForType(ResolvableType type) {Class<?> resolved = type.resolve();
    if (resolved != null && !type.hasGenerics()) {return getBeanNamesForType(resolved, true, true);
    }
    else {return doGetBeanNamesForType(type, true, true);
    }
}

public String[] getBeanNamesForType(@Nullable Class<?> type) {return getBeanNamesForType(type, true, true);
}

@Override
public String[] getBeanNamesForType(@Nullable Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {if (!isConfigurationFrozen() || type == null || !allowEagerInit) {return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);
    }
    Map<Class<?>, String[]> cache =
            (includeNonSingletons ? this.allBeanNamesByType : this.singletonBeanNamesByType);
    String[] resolvedBeanNames = cache.get(type);
    if (resolvedBeanNames != null) {return resolvedBeanNames;}
    resolvedBeanNames = doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, true);
    if (ClassUtils.isCacheSafe(type, getBeanClassLoader())) {cache.put(type, resolvedBeanNames);
    }
    return resolvedBeanNames;
}

doGetBeanNamesForType

根据 bean 定义或 factorybean 中 getObjectType 的值判断，返回与给定类型 (包括子类) 匹配的 bean 的名称。

private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {List<String> result = new ArrayList<>();

    // Check all bean definitions.
    // 遍历所有的 beanName
    for (String beanName : this.beanDefinitionNames) {
        // Only consider bean as eligible if the bean name
        // is not defined as alias for some other bean.
        // 没有别名
        if (!isAlias(beanName)) {
            try {
                // 合并 bean 的定义
                RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                // Only check bean definition if it is complete.
                if (!mbd.isAbstract() && (allowEagerInit ||
                        (mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading()) &&
                                !requiresEagerInitForType(mbd.getFactoryBeanName()))) {
                    // In case of FactoryBean, match object created by FactoryBean.
                    // 是否是 FactoryBean
                    boolean isFactoryBean = isFactoryBean(beanName, mbd);
                    BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
                    boolean matchFound =
                            (allowEagerInit || !isFactoryBean ||
                                    (dbd != null && !mbd.isLazyInit()) || containsSingleton(beanName)) &&
                            (includeNonSingletons ||
                                    (dbd != null ? mbd.isSingleton() : isSingleton(beanName))) &&
                            isTypeMatch(beanName, type);
                    if (!matchFound && isFactoryBean) {
                        // In case of FactoryBean, try to match FactoryBean instance itself next.
                        beanName = FACTORY_BEAN_PREFIX + beanName;
                        matchFound = (includeNonSingletons || mbd.isSingleton()) && isTypeMatch(beanName, type);
                    }
                    if (matchFound) {result.add(beanName);
                    }
                }
            }
            catch (CannotLoadBeanClassException ex) {if (allowEagerInit) {throw ex;}
                // Probably a class name with a placeholder: let's ignore it for type matching purposes.
                if (logger.isTraceEnabled()) {logger.trace("Ignoring bean class loading failure for bean'" + beanName + "'", ex);
                }
                onSuppressedException(ex);
            }
            catch (BeanDefinitionStoreException ex) {if (allowEagerInit) {throw ex;}
                // Probably some metadata with a placeholder: let's ignore it for type matching purposes.
                if (logger.isTraceEnabled()) {logger.trace("Ignoring unresolvable metadata in bean definition'" + beanName + "'", ex);
                }
                onSuppressedException(ex);
            }
        }
    }

    // Check manually registered singletons too.
    for (String beanName : this.manualSingletonNames) {
        try {
            // In case of FactoryBean, match object created by FactoryBean.
            if (isFactoryBean(beanName)) {if ((includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type)) {result.add(beanName);
                    // Match found for this bean: do not match FactoryBean itself anymore.
                    continue;
                }
                // In case of FactoryBean, try to match FactoryBean itself next.
                beanName = FACTORY_BEAN_PREFIX + beanName;
            }
            // Match raw bean instance (might be raw FactoryBean).
            if (isTypeMatch(beanName, type)) {result.add(beanName);
            }
        }
        catch (NoSuchBeanDefinitionException ex) {
            // Shouldn't happen - probably a result of circular reference resolution...
            if (logger.isTraceEnabled()) {logger.trace("Failed to check manually registered singleton with name'" + beanName + "'", ex);
            }
        }
    }

    return StringUtils.toStringArray(result);
}

requiresEagerInitForType

是否马上返回 bean 以确定类型

private boolean requiresEagerInitForType(@Nullable String factoryBeanName) {return (factoryBeanName != null && isFactoryBean(factoryBeanName) && !containsSingleton(factoryBeanName));
}

getBeansOfType

获取 bean 名称和实例的映射

public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type) throws BeansException {return getBeansOfType(type, true, true);
}

public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
        throws BeansException {
    // 根据类型获取到 bean 名称
    String[] beanNames = getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
    Map<String, T> result = new LinkedHashMap<>(beanNames.length);
    // 遍历所有名称，通过 bean 名称获取实例，如果不是 NullBean 加入到 result
    for (String beanName : beanNames) {
        try {Object beanInstance = getBean(beanName);
            if (!(beanInstance instanceof NullBean)) {result.put(beanName, (T) beanInstance);
            }
        }
        catch (BeanCreationException ex) {Throwable rootCause = ex.getMostSpecificCause();
            if (rootCause instanceof BeanCurrentlyInCreationException) {BeanCreationException bce = (BeanCreationException) rootCause;
                String exBeanName = bce.getBeanName();
                if (exBeanName != null && isCurrentlyInCreation(exBeanName)) {if (logger.isTraceEnabled()) {
                        logger.trace("Ignoring match to currently created bean'" + exBeanName + "':" +
                                ex.getMessage());
                    }
                    onSuppressedException(ex);
                    // Ignore: indicates a circular reference when autowiring constructors.
                    // We want to find matches other than the currently created bean itself.
                    continue;
                }
            }
            throw ex;
        }
    }
    return result;
}

getBeanNamesForAnnotation

根据注解获取 bean 的名称

public String[] getBeanNamesForAnnotation(Class<? extends Annotation> annotationType) {List<String> result = new ArrayList<>();
    // 遍历所有的 bean 的，把不是抽象类的，以及有 annotationType 注解的加入到 result
    for (String beanName : this.beanDefinitionNames) {BeanDefinition beanDefinition = getBeanDefinition(beanName);
        if (!beanDefinition.isAbstract() && findAnnotationOnBean(beanName, annotationType) != null) {result.add(beanName);
        }
    }
    // 遍历所有的 manualSingletonNames，把没有加入到 result 的以及有 annotationType 注解的加入到 result
    for (String beanName : this.manualSingletonNames) {if (!result.contains(beanName) && findAnnotationOnBean(beanName, annotationType) != null) {result.add(beanName);
        }
    }
    return StringUtils.toStringArray(result);
}

getBeansWithAnnotation

根据注解获取 bean 的实例

public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) {
    // 根据注解获取 bean 的名称
    String[] beanNames = getBeanNamesForAnnotation(annotationType);
    Map<String, Object> result = new LinkedHashMap<>(beanNames.length);
    // 遍历 bean 的名称，获取 bean 的实例
    for (String beanName : beanNames) {Object beanInstance = getBean(beanName);
        if (!(beanInstance instanceof NullBean)) {result.put(beanName, beanInstance);
        }
    }
    return result;
}

findAnnotationOnBean

根据 beanName 获取注解

public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType)
        throws NoSuchBeanDefinitionException {

    A ann = null;
    // 获取 class
    Class<?> beanType = getType(beanName);
    if (beanType != null) {
        // class 不为空，获取注解
        ann = AnnotationUtils.findAnnotation(beanType, annotationType);
    }
    // 没获取到注解，且有定义过，从定义里的 beanClass 获取
    if (ann == null && containsBeanDefinition(beanName)) {BeanDefinition bd = getMergedBeanDefinition(beanName);
        if (bd instanceof AbstractBeanDefinition) {AbstractBeanDefinition abd = (AbstractBeanDefinition) bd;
            if (abd.hasBeanClass()) {ann = AnnotationUtils.findAnnotation(abd.getBeanClass(), annotationType);
            }
        }
    }
    return ann;
}

registerResolvableDependency

注册依赖类型和自动注入值

public void registerResolvableDependency(Class<?> dependencyType, @Nullable Object autowiredValue) {Assert.notNull(dependencyType, "Dependency type must not be null");
    if (autowiredValue != null) {if (!(autowiredValue instanceof ObjectFactory || dependencyType.isInstance(autowiredValue))) {
            throw new IllegalArgumentException("Value [" + autowiredValue +
                    "] does not implement specified dependency type [" + dependencyType.getName() + "]");
        }
        this.resolvableDependencies.put(dependencyType, autowiredValue);
    }
}

isAutowireCandidate

指定的 bean 是否是自动注入的候选

public boolean isAutowireCandidate(String beanName, DependencyDescriptor descriptor)
        throws NoSuchBeanDefinitionException {return isAutowireCandidate(beanName, descriptor, getAutowireCandidateResolver());
}

protected boolean isAutowireCandidate(String beanName, DependencyDescriptor descriptor, AutowireCandidateResolver resolver)
        throws NoSuchBeanDefinitionException {String beanDefinitionName = BeanFactoryUtils.transformedBeanName(beanName);
    // 定义过的，从定义里找
    if (containsBeanDefinition(beanDefinitionName)) {return isAutowireCandidate(beanName, getMergedLocalBeanDefinition(beanDefinitionName), descriptor, resolver);
    }
    // 创建过的单例，重新创建 RootBeanDefinition
    else if (containsSingleton(beanName)) {return isAutowireCandidate(beanName, new RootBeanDefinition(getType(beanName)), descriptor, resolver);
    }
    // 都没找到，从父类找
    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;}
}

protected boolean isAutowireCandidate(String beanName, RootBeanDefinition mbd,
        DependencyDescriptor descriptor, AutowireCandidateResolver resolver) {String beanDefinitionName = BeanFactoryUtils.transformedBeanName(beanName);
    // 解析
    resolveBeanClass(mbd, beanDefinitionName);
    if (mbd.isFactoryMethodUnique && mbd.factoryMethodToIntrospect == null) {new ConstructorResolver(this).resolveFactoryMethodIfPossible(mbd);
    }
    // 从别名里找
    return resolver.isAutowireCandidate(new BeanDefinitionHolder(mbd, beanName, getAliases(beanDefinitionName)), descriptor);
}

getBeanDefinition

从 beanDefinitionMap 找 bean 的定义

public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {BeanDefinition bd = this.beanDefinitionMap.get(beanName);
    if (bd == null) {if (logger.isTraceEnabled()) {logger.trace("No bean named'" + beanName + "'found in" + this);
        }
        throw new NoSuchBeanDefinitionException(beanName);
    }
    return bd;
}

getBeanNamesIterator

获取 bean 的迭代名称，包括自定的和手动注册的

public Iterator<String> getBeanNamesIterator() {CompositeIterator<String> iterator = new CompositeIterator<>();
    iterator.add(this.beanDefinitionNames.iterator());
    iterator.add(this.manualSingletonNames.iterator());
    return iterator;
}

clearMetadataCache

public void clearMetadataCache() {super.clearMetadataCache();
    clearByTypeCache();}

freezeConfiguration

冻结当前的 bean 的信息

public void freezeConfiguration() {
    this.configurationFrozen = true;
    this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}

isConfigurationFrozen

public boolean isConfigurationFrozen() {return this.configurationFrozen;}

isBeanEligibleForMetadataCaching

是否已经冻结了或者是否已创建

protected boolean isBeanEligibleForMetadataCaching(String beanName) {return (this.configurationFrozen || super.isBeanEligibleForMetadataCaching(beanName));
}

preInstantiateSingletons

确保实例化了所有非 lazy-init 单例

public void preInstantiateSingletons() throws BeansException {if (logger.isTraceEnabled()) {logger.trace("Pre-instantiating singletons in" + this);
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    // 遍历 beanNames
    for (String beanName : beanNames) {RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // 不是抽象的，并且是单例且没有懒加载
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            //FactoryBean 的情况
            if (isFactoryBean(beanName)) {Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {final FactoryBean<?> factory = (FactoryBean<?>) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
                                        ((SmartFactoryBean<?>) factory)::isEagerInit,
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {getBean(beanName);
                    }
                }
            }
            else {
                // 直接获取
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    // 获取单例 bean 后，如果是 SmartInitializingSingleton 类型，再调用 afterSingletonsInstantiated 方法
    for (String beanName : beanNames) {Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

registerBeanDefinition

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
        throws BeanDefinitionStoreException {Assert.hasText(beanName, "Bean name must not be empty");
    Assert.notNull(beanDefinition, "BeanDefinition must not be null");
    
    if (beanDefinition instanceof AbstractBeanDefinition) {
        try {((AbstractBeanDefinition) beanDefinition).validate();}
        catch (BeanDefinitionValidationException ex) {throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                    "Validation of bean definition failed", ex);
        }
    }
    // 获取 bean 的定义
    BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
    if (existingDefinition != null) {
        // 存在的情况
        if (!isAllowBeanDefinitionOverriding()) {throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
        }
        else if (existingDefinition.getRole() < beanDefinition.getRole()) {
            // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
            if (logger.isInfoEnabled()) {
                logger.info("Overriding user-defined bean definition for bean'" + beanName +
                        "'with a framework-generated bean definition: replacing [" +
                        existingDefinition + "] with [" + beanDefinition + "]");
            }
        }
        else if (!beanDefinition.equals(existingDefinition)) {if (logger.isDebugEnabled()) {
                logger.debug("Overriding bean definition for bean'" + beanName +
                        "'with a different definition: replacing [" + existingDefinition +
                        "] with [" + beanDefinition + "]");
            }
        }
        else {if (logger.isTraceEnabled()) {
                logger.trace("Overriding bean definition for bean'" + beanName +
                        "'with an equivalent definition: replacing [" + existingDefinition +
                        "] with [" + beanDefinition + "]");
            }
        }
        this.beanDefinitionMap.put(beanName, beanDefinition);
    }
    else {
        // 不存在的情况，有 bean 创建了
        if (hasBeanCreationStarted()) {// Cannot modify startup-time collection elements anymore (for stable iteration)
            // 加锁
            synchronized (this.beanDefinitionMap) {
                // 设置以下三个信息
                this.beanDefinitionMap.put(beanName, beanDefinition);
                List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                updatedDefinitions.addAll(this.beanDefinitionNames);
                updatedDefinitions.add(beanName);
                this.beanDefinitionNames = updatedDefinitions;
                if (this.manualSingletonNames.contains(beanName)) {Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
                    updatedSingletons.remove(beanName);
                    this.manualSingletonNames = updatedSingletons;
                }
            }
        }
        else {
            // bean 还没创建，赶紧设置以下三个信息
            // Still in startup registration phase
            this.beanDefinitionMap.put(beanName, beanDefinition);
            this.beanDefinitionNames.add(beanName);
            this.manualSingletonNames.remove(beanName);
        }
        this.frozenBeanDefinitionNames = null;
    }

    if (existingDefinition != null || containsSingleton(beanName)) {resetBeanDefinition(beanName);
    }
}

removeBeanDefinition

public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {Assert.hasText(beanName, "'beanName' must not be empty");
    // 移除
    BeanDefinition bd = this.beanDefinitionMap.remove(beanName);
    // 为空说明之前不存在
    if (bd == null) {if (logger.isTraceEnabled()) {logger.trace("No bean named'" + beanName + "'found in" + this);
        }
        throw new NoSuchBeanDefinitionException(beanName);
    }
    // 已经创建 bean 了，要加锁
    if (hasBeanCreationStarted()) {// Cannot modify startup-time collection elements anymore (for stable iteration)
        synchronized (this.beanDefinitionMap) {List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames);
            updatedDefinitions.remove(beanName);
            this.beanDefinitionNames = updatedDefinitions;
        }
    }
    else {
        // Still in startup registration phase
        // 还没创建，直接移除
        this.beanDefinitionNames.remove(beanName);
    }
    this.frozenBeanDefinitionNames = null;

    resetBeanDefinition(beanName);
}

resetBeanDefinition

重置 bean 的定义

protected void resetBeanDefinition(String beanName) {
    // Remove the merged bean definition for the given bean, if already created.
    // bean 定义删除
    clearMergedBeanDefinition(beanName);

    // Remove corresponding bean from singleton cache, if any. Shouldn't usually
    // be necessary, rather just meant for overriding a context's default beans
    // (e.g. the default StaticMessageSource in a StaticApplicationContext).
    // bean 销毁
    destroySingleton(beanName);

    // Notify all post-processors that the specified bean definition has been reset.
    for (BeanPostProcessor processor : getBeanPostProcessors()) {if (processor instanceof MergedBeanDefinitionPostProcessor) {((MergedBeanDefinitionPostProcessor) processor).resetBeanDefinition(beanName);
        }
    }

    // Reset all bean definitions that have the given bean as parent (recursively).
    // 子类重置
    for (String bdName : this.beanDefinitionNames) {if (!beanName.equals(bdName)) {BeanDefinition bd = this.beanDefinitionMap.get(bdName);
            if (beanName.equals(bd.getParentName())) {resetBeanDefinition(bdName);
            }
        }
    }
}

registerSingleton

注册单例，手动注册的单例，保存在 manualSingletonNames

public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {super.registerSingleton(beanName, singletonObject);

    if (hasBeanCreationStarted()) {// Cannot modify startup-time collection elements anymore (for stable iteration)
        synchronized (this.beanDefinitionMap) {if (!this.beanDefinitionMap.containsKey(beanName)) {Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames.size() + 1);
                updatedSingletons.addAll(this.manualSingletonNames);
                updatedSingletons.add(beanName);
                this.manualSingletonNames = updatedSingletons;
            }
        }
    }
    else {
        // Still in startup registration phase
        if (!this.beanDefinitionMap.containsKey(beanName)) {this.manualSingletonNames.add(beanName);
        }
    }

    clearByTypeCache();}

destroySingleton

销毁 bean，还要移除 manualSingletonNames 的 bean

public void destroySingleton(String beanName) {super.destroySingleton(beanName);
    this.manualSingletonNames.remove(beanName);
    clearByTypeCache();}

destroySingletons

销毁所有 bean，还要移除 manualSingletonNames 的所有 bean

public void destroySingletons() {super.destroySingletons();
    this.manualSingletonNames.clear();
    clearByTypeCache();}

clearByTypeCache

清除依赖类型的映射

private void clearByTypeCache() {this.allBeanNamesByType.clear();
    this.singletonBeanNamesByType.clear();}

resolveNamedBean

通过类型解析 bean

public <T> NamedBeanHolder<T> resolveNamedBean(Class<T> requiredType) throws BeansException {NamedBeanHolder<T> namedBean = resolveNamedBean(ResolvableType.forRawClass(requiredType), null, false);
    if (namedBean != null) {return namedBean;}
    // 为空去父类查找
    BeanFactory parent = getParentBeanFactory();
    if (parent instanceof AutowireCapableBeanFactory) {return ((AutowireCapableBeanFactory) parent).resolveNamedBean(requiredType);
    }
    throw new NoSuchBeanDefinitionException(requiredType);
}

private <T> NamedBeanHolder<T> resolveNamedBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) throws BeansException {Assert.notNull(requiredType, "Required type must not be null");
    // 获取候选 bean
    String[] candidateNames = getBeanNamesForType(requiredType);

    if (candidateNames.length > 1) {List<String> autowireCandidates = new ArrayList<>(candidateNames.length);
        for (String beanName : candidateNames) {if (!containsBeanDefinition(beanName) || getBeanDefinition(beanName).isAutowireCandidate()) {autowireCandidates.add(beanName);
            }
        }
        if (!autowireCandidates.isEmpty()) {candidateNames = StringUtils.toStringArray(autowireCandidates);
        }
    }
    // 只有一个候选，就确定是这个了
    if (candidateNames.length == 1) {String beanName = candidateNames[0];
        return new NamedBeanHolder<>(beanName, (T) getBean(beanName, requiredType.toClass(), args));
    }
    else if (candidateNames.length > 1) {Map<String, Object> candidates = new LinkedHashMap<>(candidateNames.length);
        for (String beanName : candidateNames) {
            // 无参，直接获取 bean 的类型
            if (containsSingleton(beanName) && args == null) {Object beanInstance = getBean(beanName);
                candidates.put(beanName, (beanInstance instanceof NullBean ? null : beanInstance));
            }
            else {
                // 有参，通过 beanName 获取类型
                candidates.put(beanName, getType(beanName));
            }
        }
        // 获取主要的一个
        String candidateName = determinePrimaryCandidate(candidates, requiredType.toClass());
        if (candidateName == null) {
            // 没获取到，从最高级的获取
            candidateName = determineHighestPriorityCandidate(candidates, requiredType.toClass());
        }
        if (candidateName != null) {
            // 获取到了，创建一个 NamedBeanHolder 返回
            Object beanInstance = candidates.get(candidateName);
            if (beanInstance == null || beanInstance instanceof Class) {beanInstance = getBean(candidateName, requiredType.toClass(), args);
            }
            return new NamedBeanHolder<>(candidateName, (T) beanInstance);
        }
        if (!nonUniqueAsNull) {throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet());
        }
    }

    return null;
}

resolveDependency

根据工厂中定义的 bean 解析指定的依赖项

public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
        @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
    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 {Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(descriptor, requestingBeanName);
        if (result == null) {result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
        }
        return result;
    }
}

doResolveDependency

根据工厂中定义的 bean 解析指定的依赖项

public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
        @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
    try {
        // spring 第一次创建依赖的时候，会存放在 shortcut，后面就不用再解析了
        Object shortcut = descriptor.resolveShortcut(this);
        if (shortcut != null) {return shortcut;}
        // 获取注入属性的类型
        Class<?> type = descriptor.getDependencyType();
        // 处理 @Value 的值
        Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
        if (value != null) {
            // 解析 value
            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());
            try {return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
            }
            catch (UnsupportedOperationException ex) {
                // A custom TypeConverter which does not support TypeDescriptor resolution...
                return (descriptor.getField() != null ?
                        converter.convertIfNecessary(value, type, descriptor.getField()) :
                        converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
            }
        }
        // 对数组容器的处理，Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
        if (multipleBeans != null) {return multipleBeans;}
        // 对非数组、容器对象的处理，键值对
        Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
        if (matchingBeans.isEmpty()) {
            // 为空，且 required 为 true，抛异常
            if (isRequired(descriptor)) {raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
            }
            return null;
        }

        String autowiredBeanName;
        Object instanceCandidate;
        // 有多个的情况，筛选一个
        if (matchingBeans.size() > 1) {autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
            if (autowiredBeanName == null) {if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {return descriptor.resolveNotUnique(descriptor.getResolvableType(), 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.
            // 只有一个，直接返回
            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);
    }
}

resolveMultipleBeans

数组容器的情况

private Object resolveMultipleBeans(DependencyDescriptor descriptor, @Nullable String beanName,
        @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) {final 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()) {
        // 数组的情况
        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()) {
        // 容器的情况
        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) {Comparator<Object> comparator = adaptDependencyComparator(matchingBeans);
            if (comparator != null) {((List<?>) result).sort(comparator);
            }
        }
        return result;
    }
    else if (Map.class == type) {
        // map 的情况
        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;}
}

isRequired

Required 是否为 true

private boolean isRequired(DependencyDescriptor descriptor) {return getAutowireCandidateResolver().isRequired(descriptor);
}

indicatesMultipleBeans

注入属性是数组或者容器

private boolean indicatesMultipleBeans(Class<?> type) {return (type.isArray() || (type.isInterface() &&
            (Collection.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type))));
}

adaptDependencyComparator

private Comparator<Object> adaptDependencyComparator(Map<String, ?> matchingBeans) {Comparator<Object> comparator = getDependencyComparator();
    if (comparator instanceof OrderComparator) {return ((OrderComparator) comparator).withSourceProvider(createFactoryAwareOrderSourceProvider(matchingBeans));
    }
    else {return comparator;}
}

adaptOrderComparator

private Comparator<Object> adaptOrderComparator(Map<String, ?> matchingBeans) {Comparator<Object> dependencyComparator = getDependencyComparator();
    OrderComparator comparator = (dependencyComparator instanceof OrderComparator ?
            (OrderComparator) dependencyComparator : OrderComparator.INSTANCE);
    return comparator.withSourceProvider(createFactoryAwareOrderSourceProvider(matchingBeans));
}

createFactoryAwareOrderSourceProvider

private OrderComparator.OrderSourceProvider createFactoryAwareOrderSourceProvider(Map<String, ?> beans) {IdentityHashMap<Object, String> instancesToBeanNames = new IdentityHashMap<>();
    beans.forEach((beanName, instance) -> instancesToBeanNames.put(instance, beanName));
    return new FactoryAwareOrderSourceProvider(instancesToBeanNames);
}

findAutowireCandidates

protected Map<String, Object> findAutowireCandidates(@Nullable String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
    // 获取批评类型的 beanName
    String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this, requiredType, true, descriptor.isEager());
    // 存放结果
    Map<String, Object> result = new LinkedHashMap<>(candidateNames.length);
    // 如果遍历的类型是指定的类型或者子类的话，报错在 result
    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) {
        // 如果不是自引用，且符合注入的条件
        if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {addCandidateEntry(result, candidate, descriptor, requiredType);
        }
    }
    // result 为空
    if (result.isEmpty()) {
        // 注入属性是数组和容器类型，对泛型检查
        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);
            }
        }
        // 为空，且不是数组和容器类型，添加自引用
        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;
}

addCandidateEntry

加入到 candidate，在主候选项选择之前防止早期的 bean 初始化。

private void addCandidateEntry(Map<String, Object> candidates, String candidateName,
        DependencyDescriptor descriptor, Class<?> requiredType) {if (descriptor instanceof MultiElementDescriptor) {Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
        if (!(beanInstance instanceof NullBean)) {candidates.put(candidateName, beanInstance);
        }
    }
    else if (containsSingleton(candidateName) || (descriptor instanceof StreamDependencyDescriptor &&
            ((StreamDependencyDescriptor) descriptor).isOrdered())) {Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
        candidates.put(candidateName, (beanInstance instanceof NullBean ? null : beanInstance));
    }
    else {candidates.put(candidateName, getType(candidateName));
    }
}

determineAutowireCandidate

protected String determineAutowireCandidate(Map<String, Object> candidates, DependencyDescriptor descriptor) {Class<?> requiredType = descriptor.getDependencyType();
    // 如果是主要的，直接返回
    String primaryCandidate = determinePrimaryCandidate(candidates, requiredType);
    if (primaryCandidate != null) {return primaryCandidate;}
    // 如果是最高级的，直接返回
    String priorityCandidate = determineHighestPriorityCandidate(candidates, requiredType);
    if (priorityCandidate != null) {return priorityCandidate;}
    // Fallback
    // 如果不是主要和最高级的
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {String candidateName = entry.getKey();
        Object beanInstance = entry.getValue();
        if ((beanInstance != null && this.resolvableDependencies.containsValue(beanInstance)) ||
                matchesBeanName(candidateName, descriptor.getDependencyName())) {return candidateName;}
    }
    return null;
}

determinePrimaryCandidate

如果是主要的情况

protected String determinePrimaryCandidate(Map<String, Object> candidates, Class<?> requiredType) {
    String primaryBeanName = null;
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {String candidateBeanName = entry.getKey();
        Object beanInstance = entry.getValue();
        if (isPrimary(candidateBeanName, beanInstance)) {if (primaryBeanName != null) {boolean candidateLocal = containsBeanDefinition(candidateBeanName);
                boolean primaryLocal = containsBeanDefinition(primaryBeanName);
                if (candidateLocal && primaryLocal) {throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
                            "more than one'primary'bean found among candidates:" + candidates.keySet());
                }
                else if (candidateLocal) {primaryBeanName = candidateBeanName;}
            }
            else {primaryBeanName = candidateBeanName;}
        }
    }
    return primaryBeanName;
}

determineHighestPriorityCandidate

如果是最高级的情况

protected String determineHighestPriorityCandidate(Map<String, Object> candidates, Class<?> requiredType) {
    String highestPriorityBeanName = null;
    Integer highestPriority = null;
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {String candidateBeanName = entry.getKey();
        Object beanInstance = entry.getValue();
        if (beanInstance != null) {Integer candidatePriority = getPriority(beanInstance);
            if (candidatePriority != null) {if (highestPriorityBeanName != null) {if (candidatePriority.equals(highestPriority)) {throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
                                "Multiple beans found with the same priority ('" + highestPriority +
                                "') among candidates:" + candidates.keySet());
                    }
                    else if (candidatePriority < highestPriority) {
                        highestPriorityBeanName = candidateBeanName;
                        highestPriority = candidatePriority;
                    }
                }
                else {
                    highestPriorityBeanName = candidateBeanName;
                    highestPriority = candidatePriority;
                }
            }
        }
    }
    return highestPriorityBeanName;
}

isPrimary

是否为主要的，即有 primary

protected boolean isPrimary(String beanName, Object beanInstance) {if (containsBeanDefinition(beanName)) {return getMergedLocalBeanDefinition(beanName).isPrimary();}
    BeanFactory parent = getParentBeanFactory();
    return (parent instanceof DefaultListableBeanFactory &&
            ((DefaultListableBeanFactory) parent).isPrimary(beanName, beanInstance));
}

getPriority

获取优先级

protected Integer getPriority(Object beanInstance) {Comparator<Object> comparator = getDependencyComparator();
    if (comparator instanceof OrderComparator) {return ((OrderComparator) comparator).getPriority(beanInstance);
    }
    return null;
}

matchesBeanName

确定给定的候选名称是否与 bean 名或别名匹配存储在这个 bean 定义中

protected boolean matchesBeanName(String beanName, @Nullable String candidateName) {
    return (candidateName != null &&
            (candidateName.equals(beanName) || ObjectUtils.containsElement(getAliases(beanName), candidateName)));
}

isSelfReference

是否自引用

private boolean isSelfReference(@Nullable String beanName, @Nullable String candidateName) {
    return (beanName != null && candidateName != null &&
            (beanName.equals(candidateName) || (containsBeanDefinition(candidateName) &&
                    beanName.equals(getMergedLocalBeanDefinition(candidateName).getFactoryBeanName()))));
}

raiseNoMatchingBeanFound

没有匹配，抛异常

private void raiseNoMatchingBeanFound(Class<?> type, ResolvableType resolvableType, DependencyDescriptor descriptor) throws BeansException {checkBeanNotOfRequiredType(type, descriptor);

    throw new NoSuchBeanDefinitionException(resolvableType,
            "expected at least 1 bean which qualifies as autowire candidate." +
            "Dependency annotations:" + ObjectUtils.nullSafeToString(descriptor.getAnnotations()));
}

checkBeanNotOfRequiredType

private void checkBeanNotOfRequiredType(Class<?> type, DependencyDescriptor descriptor) {for (String beanName : this.beanDefinitionNames) {RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
        Class<?> targetType = mbd.getTargetType();
        // 指定的的类型是 mbd 的 targetType 子类且符合自动注入条件
        if (targetType != null && type.isAssignableFrom(targetType) &&
                isAutowireCandidate(beanName, mbd, descriptor, getAutowireCandidateResolver())) {
            // Probably a proxy interfering with target type match -> throw meaningful exception.
            Object beanInstance = getSingleton(beanName, false);
            // 获取 bean 的类型
            Class<?> beanType = (beanInstance != null && beanInstance.getClass() != NullBean.class ?
                    beanInstance.getClass() : predictBeanType(beanName, mbd));
            // 实际类型不是指定类型的子类
            if (beanType != null && !type.isAssignableFrom(beanType)) {throw new BeanNotOfRequiredTypeException(beanName, type, beanType);
            }
        }
    }
    // 从父类检查
    BeanFactory parent = getParentBeanFactory();
    if (parent instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory) parent).checkBeanNotOfRequiredType(type, descriptor);
    }
}

createOptionalDependency

创建一个 Optional 的依赖

private Optional<?> createOptionalDependency(DependencyDescriptor descriptor, @Nullable String beanName, final Object... args) {DependencyDescriptor descriptorToUse = new NestedDependencyDescriptor(descriptor) {
        @Override
        public boolean isRequired() {return false;}
        @Override
        public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory) {return (!ObjectUtils.isEmpty(args) ? beanFactory.getBean(beanName, args) :
                    super.resolveCandidate(beanName, requiredType, beanFactory));
        }
    };
    Object result = doResolveDependency(descriptorToUse, beanName, null, null);
    return (result instanceof Optional ? (Optional<?>) result : Optional.ofNullable(result));
}

toString

重写 toString 方法

public String toString() {StringBuilder sb = new StringBuilder(ObjectUtils.identityToString(this));
    sb.append(": defining beans [");
    sb.append(StringUtils.collectionToCommaDelimitedString(this.beanDefinitionNames));
    sb.append("];");
    BeanFactory parent = getParentBeanFactory();
    if (parent == null) {sb.append("root of factory hierarchy");
    }
    else {sb.append("parent:").append(ObjectUtils.identityToString(parent));
    }
    return sb.toString();}