参考源

https://www.bilibili.com/video/BV1tR4y1F75R?spm_id_from=333.337.search-card.all.click

https://www.bilibili.com/video/BV12Z4y197MU?spm_id_from=333.999.0.0

《Spring源码深度解析（第2版）》

版本

本文章基于 Spring 5.3.15

前面实现了 ClassPathXmlApplicationContext 的构造，接下来分析其调用的 getBean 方法。

以 getBean(UserDao.class) 为例。

1 AbstractApplicationContext

public <T> T getBean(Class<T> requiredType) throws BeansException {

    // 断言 Bean 工厂活动

    assertBeanFactoryActive();

    // 获取 Bean 工厂

    // 获取 Bean

    return getBeanFactory().getBean(requiredType);

}

1-1 断言 Bean 工厂活动

assertBeanFactoryActive()

protected void assertBeanFactoryActive() {

   if (!this.active.get()) {

      if (this.closed.get()) {

         // 获取显示名称

         throw new IllegalStateException(getDisplayName() + " has been closed already");

      }

      else {

         // 获取显示名称

         throw new IllegalStateException(getDisplayName() + " has not been refreshed yet");

      }

   }

}

获取显示名称前面已经分析过了，这里不再分析。

1-1 获取 Bean 工厂

getBeanFactory()

2 AbstractRefreshableApplicationContext

public final ConfigurableListableBeanFactory getBeanFactory() {

   DefaultListableBeanFactory beanFactory = this.beanFactory;

   if (beanFactory == null) {

      throw new IllegalStateException("BeanFactory not initialized or already closed - " + "call 'refresh' before accessing beans via the ApplicationContext");

   }

   return beanFactory;

}

if (beanFactory == null) 由于前面定义了 beanFactory，这里直接返回。

1 AbstractApplicationContext

1-1 获取 Bean

getBean(requiredType)

3 DefaultListableBeanFactory

public <T> T getBean(Class<T> requiredType) throws BeansException {

   // 获取 Bean

   return getBean(requiredType, (Object[]) null);

}

public <T> T getBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {

   Assert.notNull(requiredType, "Required type must not be null");

   // 解析 Bean

   Object resolved = resolveBean(ResolvableType.forRawClass(requiredType), args, false);

   if (resolved == null) {

      throw new NoSuchBeanDefinitionException(requiredType);

   }

   return (T) resolved;

}

3-1 解析 Bean

resolveBean(ResolvableType.forRawClass(requiredType), args, false)

private <T> T resolveBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) {

    // 解析 Bean 命名

    NamedBeanHolder<T> namedBean = resolveNamedBean(requiredType, args, nonUniqueAsNull);

    if (namedBean != null) {

        return namedBean.getBeanInstance();

    }

    // 获取父级 Bean 工厂

    BeanFactory parent = getParentBeanFactory();

    if (parent instanceof DefaultListableBeanFactory) {

        // 解析 Bean，递归调用

        return ((DefaultListableBeanFactory) parent).resolveBean(requiredType, args, nonUniqueAsNull);

    }

    else if (parent != null) {

        ObjectProvider<T> parentProvider = parent.getBeanProvider(requiredType);

        if (args != null) {

            return parentProvider.getObject(args);

        }

        else {

            return (nonUniqueAsNull ? parentProvider.getIfUnique() : parentProvider.getIfAvailable());

        }

    }

    return null;

}

3-2 解析 Bean 命名

resolveNamedBean(requiredType, args, nonUniqueAsNull)

private <T> NamedBeanHolder<T> resolveNamedBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) throws BeansException {

   Assert.notNull(requiredType, "Required type must not be null");

   // 获取类型的 Bean 名称

   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);

      }

   }

   if (candidateNames.length == 1) {

      // 解析 Bean 命名

      return resolveNamedBean(candidateNames[0], requiredType, args);

   } else if (candidateNames.length > 1) {

      Map<String, Object> candidates = CollectionUtils.newLinkedHashMap(candidateNames.length);

      for (String beanName : candidateNames) {

         if (containsSingleton(beanName) && args == null) {

            Object beanInstance = getBean(beanName);

            candidates.put(beanName, (beanInstance instanceof NullBean ? null : beanInstance));

         } else {

            candidates.put(beanName, getType(beanName));

         }

      }

      // 确定主要候选

      String candidateName = determinePrimaryCandidate(candidates, requiredType.toClass());

      if (candidateName == null) {

         // 确定最高优先级候选

         candidateName = determineHighestPriorityCandidate(candidates, requiredType.toClass());

      }

      if (candidateName != null) {

         Object beanInstance = candidates.get(candidateName);

         if (beanInstance == null) {

            return null;

         }

         if (beanInstance instanceof Class) {

            // 解析 Bean 命名

            return resolveNamedBean(candidateName, requiredType, args);

         }

         return new NamedBeanHolder<>(candidateName, (T) beanInstance);

      }

      if (!nonUniqueAsNull) {

         throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet());

      }

   }

   return null;

}

3-3 确定主要候选

determinePrimaryCandidate(candidates, requiredType.toClass())

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;

}

3-3 确定最高优先级候选

determineHighestPriorityCandidate(candidates, requiredType.toClass())

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;

}

巴特西

Spring源码 19 IOC getBean

1 AbstractApplicationContext

1-1 断言 Bean 工厂活动

1-1 获取 Bean 工厂

2 AbstractRefreshableApplicationContext

1 AbstractApplicationContext

1-1 获取 Bean

3 DefaultListableBeanFactory

3-1 解析 Bean

3-2 解析 Bean 命名

3-3 确定主要候选

3-3 确定最高优先级候选

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