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【spring源码分析】IOC容器初始化(七)

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前言:在【spring源码分析】IOC容器初始化(六)中分析到从单例缓存中加载bean对象,由于篇幅原因对于其中的核心函数 FactoryBeanRegistrySupport#getObjectFromFactoryBean并会进行详细分析,本文

前言:在【spring源码分析】IOC容器初始化(六)中分析到从单例缓存中加载bean对象,由于篇幅原因对于其中的核心函数

FactoryBeanRegistrySupport#getObjectFromFactoryBean并会进行详细分析,本文将继续对bean加载过程的分析。


FactoryBeanRegistrySupport#getObjectFromFactoryBean

 1 protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
 2         // 为单例模式,其缓存中存在该bean实例
 3         if (factory.isSingleton() && containsSingleton(beanName)) {
 4             /**
 5              * 做同步,内部其实使用的就是{@link DefaultSingletonBeanRegistry#singletonObjects}
 6              */
 7             synchronized (getSingletonMutex()) {
 8                 // 从缓存中获取指定的factoryBean
 9                 Object object = this.factoryBeanObjectCache.get(beanName);
10                 if (object == null) {
11                     // 为空,则从FactoryBean中获取对象
12                     object = doGetObjectFromFactoryBean(factory, beanName);
13                     // Only post-process and store if not put there already during getObject() call above
14                     // (e.g. because of circular reference processing triggered by custom getBean calls)
15                     // 再次从缓存中获取bean对象,主要是因为循环依赖
16                     Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
17                     if (alreadyThere != null) {
18                         object = alreadyThere;
19                     } else {
20                         // 需要后续处理
21                         if (shouldPostProcess) {
22                             // 如果该Bean处于创建中,则返回处理对象,而不是存储该对象
23                             if (isSingletonCurrentlyInCreation(beanName)) {
24                                 // Temporarily return non-post-processed object, not storing it yet..
25                                 return object;
26                             }
27                             // 单例bean的前置处理 用于添加标志,当前bean正处于创建中
28                             beforeSingletonCreation(beanName);
29                             try {
30                                 // 对FactoryBean获取的对象进行后置处理,返回生成的对象
31                                 object = postProcessObjectFromFactoryBean(object, beanName);
32                             } catch (Throwable ex) {
33                                 throw new BeanCreationException(beanName,
34                                                                 "Post-processing of FactoryBean‘s singleton object failed", ex);
35                             } finally {
36                                 // 单例bean的后置处理 和前置处理相反,前置添加,后置移除 移除标志,当前bean不处于创建中
37                                 afterSingletonCreation(beanName);
38                             }
39                         }
40                         // 添加到factoryBeanObjectCache中进行缓存
41                         if (containsSingleton(beanName)) {
42                             this.factoryBeanObjectCache.put(beanName, object);
43                         }
44                     }
45                 }
46                 return object;
47             }
48         } else {
49             // 不满足第一个条件,不是单例,或者缓存中不存在,则从FactoryBean中获取对象
50             Object object = doGetObjectFromFactoryBean(factory, beanName);
51             // 需要后续处理
52             if (shouldPostProcess) {
53                 try {
54                     // 对FactoryBean获取的对象进行后处理
55                     // 返回生成的对象
56                     object = postProcessObjectFromFactoryBean(object, beanName);
57                 } catch (Throwable ex) {
58                     throw new BeanCreationException(beanName, "Post-processing of FactoryBean‘s object failed", ex);
59                 }
60             }
61             return object;
62         }
63     }

分析:

函数分两大分支:

#1.单例且singletonObjects缓存中存在(该分支为同步方法)

  • #1.1:FactoryBean为单例,并且缓存中存在该bean对象(containsSingleton方法其实就是判断singletonObjects集合中是否存在bean对象),首先从缓存中获取factoryBean对象object,如果object=null,则从doGetObjectFromFactoryBean方法中获取对象。注意:这里再次从factoryBeanObjectCache缓存中尝试获取对象(主要是循环依赖问题,有可能这时该bean对象已经加载了,就不用再次加载了),如果缓存中已存在bean对象,则使用缓存中对象,并直接返回。
  • #1.2:如果factoryBeanObjectCache缓存中不存在对象且需要后置处理,则首先判断该bean对象是否正在被创建,如果是,则直接返回,注意这里未进行缓存;然后对单例bean进行前置添加处理(beforeSingletonCreation)、后置处理(postProcessObjectFromFactoryBean)、后置移除标志处理(afterSingletonCreation)。
  • #1.3:最后将缓存生成的bean对象

#2.不满足(#1)中的任何一条件

  • 首先从doGetObjectFromFactoryBean方法中获取获取bean对象,如果需要后置处理,则调用postProcessObjectFromFactoryBean方法进行处理,最后返回生成过的bean对象。

在上述分析中涉及到几个函数,下面一一进行分析。

FactoryBeanRegistrySupport#doGetObjectFromFactoryBean

 1 private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
 2             throws BeanCreationException {
 3 
 4         Object object;
 5         try {
 6             // 如果权限不为空
 7             if (System.getSecurityManager() != null) {
 8                 AccessControlContext acc = getAccessControlContext();
 9                 try {
10                     // 从FactoryBean中获取Bean对象[factory::getObject] 其实与else分支一样的
11                     object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc);
12                 } catch (PrivilegedActionException pae) {
13                     throw pae.getException();
14                 }
15             } else {
16                 // 如果权限为空,则从Factory中获取Bean对象
17                 object = factory.getObject();
18             }
19         } catch (FactoryBeanNotInitializedException ex) {
20             throw new BeanCurrentlyInCreationException(beanName, ex.toString());
21         } catch (Throwable ex) {
22             throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
23         }
24 
25         // 进行一波校验
26         // Do not accept a null value for a FactoryBean that‘s not fully
27         // initialized yet: Many FactoryBeans just return null then.
28         if (object == null) {
29             // 如果bean正在被创建,则抛出异常
30             if (isSingletonCurrentlyInCreation(beanName)) {
31                 throw new BeanCurrentlyInCreationException(
32                         beanName, "FactoryBean which is currently in creation returned null from getObject");
33             }
34             object = new NullBean();
35         }
36         return object;
37     }

分析:

根据是否具有权限,通过FactoryBean#getObject获取bean对象,如果bean对象为null且正在被创建,则抛出异常,否则实例化一个NullBean对象进行返回。

DefaultSingletonBeanRegistry#isSingletonCurrentlyInCreation

 1     /**
 2      * 正在创建中的单例 Bean 的名字的集合
 3      * Names of beans that are currently in creation.
 4      */
 5     private final Set<String> singletonsCurrentlyInCreation =
 6             Collections.newSetFromMap(new ConcurrentHashMap<>(16));
 7 
 8 public boolean isSingletonCurrentlyInCreation(String beanName) {
 9         return this.singletonsCurrentlyInCreation.contains(beanName);
10     }

分析:

该函数判断bean是否正处于创建之中,该方法要与beforeSingletonCreation和afterSingletonCreation配合起来分析才能明白其重要性,他们记录了bean的加载状态,是检查当前bean是否处于创建中的关键处,对解决bean的循环依赖起着重要作用。

DefaultSingletonBeanRegistry#beforeSingletonCreation

1     protected void beforeSingletonCreation(String beanName) {
2         // 这里会添加到正在创建bean的集合中
3         // 注意第一个条件,如果存在,则为false,直接短路
4         // 只有当第一个条件不存在[false]时,才会去进行添加操作
5         if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
6             throw new BeanCurrentlyInCreationException(beanName);
7         }
8     }

分析:

注意这里就会将正在创建的beanName添加到singletonsCurrentlyInCreation集合中,第一个条件是判断该bean是否不会被检测。

DefaultSingletonBeanRegistry#afterSingletonCreation

1 protected void afterSingletonCreation(String beanName) {
2         if (!this.inCreationCheckExclusions.contains(beanName)
3                 && !this.singletonsCurrentlyInCreation.remove(beanName)) { // 移除
4             // 如果移除失败,则抛出IllegalStateException异常
5             throw new IllegalStateException("Singleton ‘" + beanName + "‘ isn‘t currently in creation");
6         }
7     }

分析:

afterSingletonCreation方法与beforeSingletonCreation方法的功能相反,用于将beanName移除正在创建的集合singletonsCurrentlyInCreation,表明bean创建完成。

postProcessObjectFromFactoryBean

该方法的默认实现,就是返回当前bean对象。

1 // FactoryBeanRegistrySupport
2 protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
3         return object;
4     }

当然,子类可以对该方法进行重写。

 1 // AbstractAutowireCapableBeanFactory
 2 
 3     protected Object postProcessObjectFromFactoryBean(Object object, String beanName) {
 4         return applyBeanPostProcessorsAfterInitialization(object, beanName);
 5     }
 6 
 7 public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 8             throws BeansException {
 9 
10         Object result = existingBean;
11         // 遍历BeanPostProcessor
12         for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
13             // 进行处理
14             // TODO: 2019/4/2 具体处理过程需详细查看,这里先走大流程
15             Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
16             // 返回为空,则返回传入的Object对象
17             if (current == null) {
18                 return result;
19             }
20             // 修改result
21             result = current;
22         }
23         return result;
24     }

分析:

这里主要是遍历BeanPostProcessor,然后对bean对象进行处理,关于后置处理器的分析后面再做分析。

到这里从单例缓存中获取bean对象的相应源码已分析完成,接下来看单例缓存中无bean对象时,Spring的处理流程,再次将getBean的切入点代码贴出来。

  1 protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
  2                               @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
  3 
  4         // .........省略从单例缓存中获取bean对象的代码
  5         } else {
  6             // Fail if we‘re already creating this bean instance:
  7             // We‘re assumably within a circular reference.
  8             // Spring只能解决单例模式下的循环依赖,在原型模式下如果存在循环依赖则抛出异常
  9             // 这里检测原型模式下,该bean是否在加载,如果在加载则抛出异常
 10             if (isPrototypeCurrentlyInCreation(beanName)) {
 11                 throw new BeanCurrentlyInCreationException(beanName);
 12             }
 13 
 14             // 如果当前容器中没有找到,则从父类容器中加载
 15             // Check if bean definition exists in this factory.
 16             BeanFactory parentBeanFactory = getParentBeanFactory();
 17             /**
 18              * 调用{@link DefaultListableBeanFactory#containsBeanDefinition(String)}方法
 19              * 其实就是在beanDefinitionMap中判断是否存在beanName对应的BeanDefinition
 20              */
 21             if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
 22                 // Not found -> check parent.
 23                 // 确定原始的beanName
 24                 String nameToLookup = originalBeanName(name);
 25                 // 如果父类容器为AbstractBeanFactory,则委托父类处理
 26                 if (parentBeanFactory instanceof AbstractBeanFactory) {
 27                     return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
 28                             nameToLookup, requiredType, args, typeCheckOnly);
 29                 } else if (args != null) { // 用明确的args从parentBeanFactory中,获取Bean对象
 30                     // Delegation to parent with explicit args.
 31                     // 委托给父类构造函数getBean()处理
 32                     return (T) parentBeanFactory.getBean(nameToLookup, args);
 33                 } else if (requiredType != null) { // 用明确的requiredType从parentBeanFactory中,获取Bean对象
 34                     // No args -> delegate to standard getBean method.
 35                     // 没有args,委托给标准的getBean()处理
 36                     return parentBeanFactory.getBean(nameToLookup, requiredType);
 37                 } else {
 38                     // 直接使用nameToLookup从parentBeanFactory中获取Bean对象
 39                     return (T) parentBeanFactory.getBean(nameToLookup);
 40                 }
 41             }
 42 
 43             // 如果不仅仅是做类型检查,而是创建bean,这里需要记录
 44             if (!typeCheckOnly) {
 45                 markBeanAsCreated(beanName);
 46             }
 47 
 48             try {
 49                 /**
 50                  * 从容器中获取beanName对应的GenericBeanDefinition对象,并转换成RootBeanDefinition对象
 51                  * GenericBeanDefinition的创建{@link BeanDefinitionReaderUtils#createBeanDefinition}方法
 52                  */
 53                 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
 54                 // 检查合并的BeanDefinition
 55                 checkMergedBeanDefinition(mbd, beanName, args);
 56 
 57                 // Guarantee initialization of beans that the current bean depends on.
 58                 // 处理所依赖的bean
 59                 String[] dependsOn = mbd.getDependsOn();
 60                 if (dependsOn != null) {
 61                     for (String dep : dependsOn) {
 62                         // 若给定的依赖bean已经注册为依赖给定的bean
 63                         // 即循环依赖情况,抛出BeanCreationException异常
 64                         if (isDependent(beanName, dep)) {
 65                             throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 66                                                             "Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dep + "‘");
 67                         }
 68                         // 缓存依赖调用
 69                         registerDependentBean(dep, beanName);
 70                         try {
 71                             // 递归处理依赖 Bean
 72                             getBean(dep);
 73                         } catch (NoSuchBeanDefinitionException ex) {
 74                             throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 75                                                             "‘" + beanName + "‘ depends on missing bean ‘" + dep + "‘", ex);
 76                         }
 77                     }
 78                 }
 79                 // bean实例化
 80                 // Create bean instance.
 81                 // 单例模式
 82                 /**
 83                  * 这里有个已创建bean的重要方法createBean
 84                  * {@link AbstractAutowireCapableBeanFactory#createBean(String, RootBeanDefinition, Object[])}
 85                  */
 86                 if (mbd.isSingleton()) {
 87                     sharedInstance = getSingleton(beanName, () -> {
 88                         try {
 89                             return createBean(beanName, mbd, args);
 90                         } catch (BeansException ex) {
 91                             // Explicitly remove instance from singleton cache: It might have been put there
 92                             // eagerly by the creation process, to allow for circular reference resolution.
 93                             // Also remove any beans that received a temporary reference to the bean.
 94                             // 显式从单例缓存中删除Bean实例
 95                             // 因为单例模式下为了解决循环依赖,可能它已经存在,所以销毁它
 96                             destroySingleton(beanName);
 97                             throw ex;
 98                         }
 99                     });
100                     bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
101                 } else if (mbd.isPrototype()) { // 原型模式
102                     // It‘s a prototype -> create a new instance.
103                     Object prototypeInstance = null;
104                     try {
105                         // 前置处理
106                         beforePrototypeCreation(beanName);
107                         /**
108                          * 创建bean {@link AbstractAutowireCapableBeanFactory#createBean}
109                          */
110                         prototypeInstance = createBean(beanName, mbd, args);
111                     } finally {
112                         /**
113                          * 后置处理 与前置处理相反从{@link prototypesCurrentlyInCreation}中移除
114                          */
115                         afterPrototypeCreation(beanName);
116                     }
117                     bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
118                 } else { //其他作用域
119                     // 获得scopeName对应的Scope对象
120                     String scopeName = mbd.getScope();
121                     final Scope scope = this.scopes.get(scopeName);
122                     if (scope == null) {
123                         throw new IllegalStateException("No Scope registered for scope name ‘" + scopeName + "‘");
124                     }
125                     try {
126                         /**
127                          * 从指定的scope下创建bean
128                          * {@link SimpleThreadScope#get方法}
129                          */
130                         Object scopedInstance = scope.get(beanName, () -> {
131                             beforePrototypeCreation(beanName);
132                             try {
133                                 return createBean(beanName, mbd, args);
134                             } finally {
135                                 afterPrototypeCreation(beanName);
136                             }
137                         });
138                         bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
139                     } catch (IllegalStateException ex) {
140                         throw new BeanCreationException(beanName,
141                                                         "Scope ‘" + scopeName + "‘ is not active for the current thread; consider " +
142                                                                 "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
143                                                         ex);
144                     }
145                 }
146             } catch (BeansException ex) {
147                 cleanupAfterBeanCreationFailure(beanName);
148                 throw ex;
149             }
150         }
151 
152         // 检查需要的类型是否符合bean的实际类型
153         // Check if required type matches the type of the actual bean instance.
154         if (requiredType != null && !requiredType.isInstance(bean)) {
155             try {
156                 T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
157                 if (convertedBean == null) {
158                     throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
159                 }
160                 return convertedBean;
161             } catch (TypeMismatchException ex) {
162                 if (logger.isTraceEnabled()) {
163                     logger.trace("Failed to convert bean ‘" + name + "‘ to required type ‘" +
164                                          ClassUtils.getQualifiedName(requiredType) + "‘", ex);
165                 }
166                 throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
167             }
168         }
169         return (T) bean;
170     }

分析:

#1.首先通过AbstractBeanFactory#isPrototypeCurrentlyInCreation检查bean对象是否处于原型模式下的循环依赖,因为Spring只能解决单例模式下的循环依赖,如果在原型模式下也存在该bean对象,则会抛出异常。

 1 // AbstractBeanFactory
 2     /**
 3      * 原型模式下存储beanName的ThreadLocal<br/>
 4      * Names of beans that are currently in creation.
 5      */
 6     private final ThreadLocal<Object> prototypesCurrentlyInCreation =
 7             new NamedThreadLocal<>("Prototype beans currently in creation");
 8     protected boolean isPrototypeCurrentlyInCreation(String beanName) {
 9         Object curVal = this.prototypesCurrentlyInCreation.get();
10         return (curVal != null &&
11                 (curVal.equals(beanName) //相等
12                         || (curVal instanceof Set && ((Set<?>) curVal).contains(beanName)))); // 包含
13     }
  • 这里就是检查原型模式的ThreadLocal中是否已经存在对应的beanName。

#2.AbstractBeanFactory#getParentBeanFactory检查其父类BeanFactory是否存在,如果存在且beanDefinitionMap中不存在该BeanDefinition,则委托其父类通过getBean方法获取bean对象。注意这里首先会通过originalBeanName方法获取原始beanName。

1 // AbstractBeanFactory
2     protected String originalBeanName(String name) {
3         String beanName = transformedBeanName(name);
4         if (name.startsWith(FACTORY_BEAN_PREFIX)) {
5             // 如果beanName以&开头,则在加上&进行返回 因为transformedBeanName中会去掉&
6             beanName = FACTORY_BEAN_PREFIX + beanName;
7         }
8         return beanName;
9     }
  • 首先通过transformedBeanName(该方法前面已经分析)获取真正的beanName,如果name以"&"开头,则将beanName加上"&"符号,因为transformedBeanName方法会去掉"&"符号。

#3.判断bean是否需要做类型检查,如果不仅仅做类型检查,则需要调用markBeanAsCreated函数进行记录。

 1 // AbstractBeanFactory
 2     /**
 3      * 已创建Bean的名字集合<br/>
 4      * Names of beans that have already been created at least once.
 5      */
 6     private final Set<String> alreadyCreated = Collections.newSetFromMap(new ConcurrentHashMap<>(256));
 7 
 8 
 9 protected void markBeanAsCreated(String beanName) {
10         // 没有创建
11         if (!this.alreadyCreated.contains(beanName)) {
12             // 做同步
13             synchronized (this.mergedBeanDefinitions) {
14                 // 再次进行检查,DoubleCheck模式
15                 if (!this.alreadyCreated.contains(beanName)) {
16                     // Let the bean definition get re-merged now that we‘re actually creating
17                     // the bean... just in case some of its metadata changed in the meantime.
18                     // 从mergedBeanDefinitions中删除beanName,并在下次访问时重新创建它
19                     clearMergedBeanDefinition(beanName);
20                     // 添加到已创建bean集合中
21                     this.alreadyCreated.add(beanName);
22                 }
23             }
24         }
25     }

#4. 接下来将对BeanDefinition进行转换,因为最开始创建的BeanDefinition类型为GenericBeanDefinition,getMergedLocalBeanDefinition方法在前面已经进行了分析,这里不在赘述。

#5.调用checkMergedBeanDefinition对转换后的RootBeanDefinition,如果RootBeanDefinition仍为抽象的,则抛出异常,这里抽象的对象还不能进行实例化。代码如下:

1 // AbstractBeanFactory
2 protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName, @Nullable Object[] args)
3             throws BeanDefinitionStoreException {
4 
5         if (mbd.isAbstract()) {
6             throw new BeanIsAbstractException(beanName);
7         }
8     }

#6.处理依赖,如果在加载bean对象时,发现它有依赖bean的话,那么在初始化该bean的时候需要先初始化依赖的bean对象

 1 // 处理所依赖的bean
 2                 String[] dependsOn = mbd.getDependsOn();
 3                 if (dependsOn != null) {
 4                     for (String dep : dependsOn) {
 5                         // 若给定的依赖bean已经注册为依赖给定的bean
 6                         // 即循环依赖情况,抛出BeanCreationException异常
 7                         if (isDependent(beanName, dep)) {
 8                             throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 9                                                             "Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dep + "‘");
10                         }
11                         // 缓存依赖调用
12                         registerDependentBean(dep, beanName);
13                         try {
14                             // 递归处理依赖 Bean
15                             getBean(dep);
16                         } catch (NoSuchBeanDefinitionException ex) {
17                             throw new BeanCreationException(mbd.getResourceDescription(), beanName,
18                                                             "‘" + beanName + "‘ depends on missing bean ‘" + dep + "‘", ex);
19                         }
20                     }
21                 }

分析:

DefaultSingletonBeanRegistry#isDependent

 1 protected boolean isDependent(String beanName, String dependentBeanName) {
 2         synchronized (this.dependentBeanMap) {
 3             return isDependent(beanName, dependentBeanName, null);
 4         }
 5     }
 6 private boolean isDependent(String beanName, String dependentBeanName, @Nullable Set<String> alreadySeen) {
 7         // alreadySeen 已经检测的依赖bean
 8         if (alreadySeen != null && alreadySeen.contains(beanName)) {
 9             return false;
10         }
11         // 获取原始的beanName
12         String canonicalName = canonicalName(beanName);
13         // 获取当前beanName的依赖集合
14         Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
15         // 不存在,则说明不存在注册依赖
16         if (dependentBeans == null) {
17             return false;
18         }
19         // 存在,则证明已经存在注册依赖
20         if (dependentBeans.contains(dependentBeanName)) {
21             return true;
22         }
23         // 递归检测依赖
24         for (String transitiveDependency : dependentBeans) {
25             if (alreadySeen == null) {
26                 alreadySeen = new HashSet<>();
27             }
28             // 添加到alreadySeen
29             alreadySeen.add(beanName);
30             // 递推
31             if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) {
32                 return true;
33             }
34         }
35         return false;
36     }

分析:

这里通过一些列判断,是否依赖的bean是否已经注入,如果注入则返回true,否则返回false。

#7.如果依赖检测通过,则调用registerDependentBean对依赖bean进行注入。

 1 // DefaultSingletonBeanRegistry
 2 
 3     /**
 4      * 保存的是依赖beanName  映射关系:beanName --> 依赖beanName的集合<br/>
 5      * Map between dependent bean names: bean name to Set of dependent bean names.
 6      */
 7     private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<>(64);
 8 
 9     /**
10      * 保存的是依赖 beanName 之间的映射关系:依赖 beanName - > beanName 的集合
11      * Map between depending bean names: bean name to Set of bean names for the bean‘s dependencies.
12      */
13     private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<>(64);
14 
15 public void registerDependentBean(String beanName, String dependentBeanName) {
16         // 获取beanName
17         String canonicalName = canonicalName(beanName);
18 
19         // 做同步 添加<canonicalName,<dependentBeanName>>到dependentBeanMap中
20         synchronized (this.dependentBeanMap) {
21             Set<String> dependentBeans =
22                     this.dependentBeanMap.computeIfAbsent(canonicalName, k -> new LinkedHashSet<>(8));
23             if (!dependentBeans.add(dependentBeanName)) {
24                 return;
25             }
26         }
27         // 做同步 添加<canonicalName,<dependentBeanName>>到dependenciesForBeanMap中
28         synchronized (this.dependenciesForBeanMap) {
29             Set<String> dependenciesForBean =
30                     this.dependenciesForBeanMap.computeIfAbsent(dependentBeanName, k -> new LinkedHashSet<>(8));
31             dependenciesForBean.add(canonicalName);
32         }
33     }

分析:

这里就是就是将依赖的beanName关系添加到dependentBeanMap、dependenciesForBeanMap集合中。

#8.最后通过getBean方法实例化依赖bean对象,该方法会在后面进行分析。

各种scope的Bean创建

在经过单例缓存中获取bean对象、从父类工厂中获取bean对象、处理依赖bean这三步后,接下来来到对各种scope的bean的创建。首先是单例模式bean对象的创建,我们知道singleton为Spring的bean的默认作用域,当然除了singleton之外,还有prototype、request等其他的scope。

#1.singleton的初始化代码如下

 1 // AbstractBeanFactory
 2 
 3 if (mbd.isSingleton()) {
 4                     sharedInstance = getSingleton(beanName, () -> {
 5                         try {
 6                             return createBean(beanName, mbd, args);
 7                         } catch (BeansException ex) {
 8                             // Explicitly remove instance from singleton cache: It might have been put there
 9                             // eagerly by the creation process, to allow for circular reference resolution.
10                             // Also remove any beans that received a temporary reference to the bean.
11                             // 显式从单例缓存中删除Bean实例
12                             // 因为单例模式下为了解决循环依赖,可能它已经存在,所以销毁它
13                             destroySingleton(beanName);
14                             throw ex;
15                         }
16                     });
17                     bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
18 }

分析:

单例模式bean的初始化是从getSingleton方法开始,当然这里还有一个重要的createBean方法,该方法我们留在后面进行分析,首先来看getSingleton方法。

 1 // DefaultSingletonBeanRegistry
 2 
 3 public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
 4         Assert.notNull(beanName, "Bean name must not be null");
 5         // 做同步
 6         synchronized (this.singletonObjects) {
 7             // 从缓存中检查一遍
 8             // 因为singlton模式其实已经复用了创建的bean,所以该步骤必须检查
 9             Object singletonObject = this.singletonObjects.get(beanName);
10             // 为空,开始进行加载
11             if (singletonObject == null) {
12                 if (this.singletonsCurrentlyInDestruction) {
13                     throw new BeanCreationNotAllowedException(beanName,
14                                                               "Singleton bean creation not allowed while singletons of this factory are in destruction " +
15                                                                       "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
16                 }
17                 if (logger.isDebugEnabled()) {
18                     logger.debug("Creating shared instance of singleton bean ‘" + beanName + "‘");
19                 }
20                 // 加载前置处理 其实就是打一个标记
21                 beforeSingletonCreation(beanName);
22                 // 首先将新的newSingleton设置为false
23                 boolean newSingleton = false;
24                 boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
25                 if (recordSuppressedExceptions) {
26                     this.suppressedExceptions = new LinkedHashSet<>();
27                 }
28                 try {
29                     // 初始化bean
30                     // 该过程其实是调用createBean()方法 这里是一个回调方法
31                     singletonObject = singletonFactory.getObject();
32                     newSingleton = true;
33                 } catch (IllegalStateException ex) {
34                     // Has the singleton object implicitly appeared in the meantime ->
35                     // if yes, proceed with it since the exception indicates that state.
36                     singletonObject = this.singletonObjects.get(beanName);
37                     if (singletonObject == null) {
38                         throw ex;
39                     }
40                 } catch (BeanCreationException ex) {
41                     if (recordSuppressedExceptions) {
42                         for (Exception suppressedException : this.suppressedExceptions) {
43                             ex.addRelatedCause(suppressedException);
44                         }
45                     }
46                     throw ex;
47                 } finally {
48                     if (recordSuppressedExceptions) {
49                         this.suppressedExceptions = null;
50                     }
51                     // 一堆异常处理后,进行后置处理 移除标志
52                     afterSingletonCreation(beanName);
53                 }
54                 // 新的bean 加入缓存中
55                 if (newSingleton) {
56                     addSingleton(beanName, singletonObject);
57                 }
58             }
59             return singletonObject;
60         }
61     }

分析(该方法同样为同步方法):

该方法其实并未真正创建bean对象,获取bean对象的核心点在于singletonObject = singletonFactory.getObject(),但该方法是由createBean回调产生的。这里仅仅是做了一部分准备和预处理步骤:

  • 再次从缓存中检查bean是否已经加载过,如果缓存中存在则直接返回。
  • beforeSingletonCreation前面已经分析过,记录加载单例bean的状态,表示正在被加载。
  • 然后调用singletonFactory.getObject方法实例化bean对象
  • afterSingletonCreation前面也分析过了,移除bean正在被加载的标志。
  • 将生成的bean对象加入缓存。

DefaultSingletonBeanRegistry#addSingleton

 1     /**
 2      * Cache of singleton objects: bean name to bean instance.
 3      * 存放的是单例 bean 的映射。
 4      * <p>
 5      * 对应关系为 bean name --> bean instance
 6      */
 7     private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
 8 
 9     /**
10      * Cache of singleton factories: bean name to ObjectFactory.<br/>
11      * 存放的是 ObjectFactory,可以理解为创建单例 bean 的 factory 。
12      * <p>
13      * 对应关系是 bean name --> ObjectFactory
14      */
15     private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
16 
17     /**
18      * Cache of early singleton objects: bean name to bean instance.<br/>
19      * 存放的是早期的 bean,对应关系也是 bean name --> bean instance。
20      * <p>
21      * 它与 {@link #singletonFactories} 区别在于 earlySingletonObjects 中存放的 bean 不一定是完整。
22      * <p>
23      * 从 {@link #getSingleton(String)} 方法中,我们可以了解,bean 在创建过程中就已经加入到 earlySingletonObjects 中了。
24      * 所以当在 bean 的创建过程中,就可以通过 getBean() 方法获取。
25      * <p>
26      * 这个 Map 也是【循环依赖】的关键所在。
27      */
28     private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
29 
30     /**
31      * 存储已经注册的单例 进行缓存<br/>
32      * Set of registered singletons, containing the bean names in registration order.
33      */
34     private final Set<String> registeredSingletons = new LinkedHashSet<>(256);    
35 
36     protected void addSingleton(String beanName, Object singletonObject) {
37         synchronized (this.singletonObjects) {
38             this.singletonObjects.put(beanName, singletonObject);
39             this.singletonFactories.remove(beanName);
40             this.earlySingletonObjects.remove(beanName);
41             this.registeredSingletons.add(beanName);
42         }
43     }

分析:

一个put、两个remove、一个add。

  • 由于已经实例化了bean,因此需要将单例bean进行缓存,singletonObjects.put。
  • 同理单例BeanFactory和提前曝光的bean也需要移除,singletonFactories.remove和earlySingletonObjects.remove。
  • registeredSingletons.add,已实例化的bean需要进行注册。

#2.原型模式

 1 if (mbd.isPrototype()) { // 原型模式
 2                     // It‘s a prototype -> create a new instance.
 3                     Object prototypeInstance = null;
 4                     try {
 5                         // 前置处理
 6                         beforePrototypeCreation(beanName);
 7                         /**
 8                          * 创建bean {@link AbstractAutowireCapableBeanFactory#createBean}
 9                          */
10                         prototypeInstance = createBean(beanName, mbd, args);
11                     } finally {
12                         /**
13                          * 后置处理 与前置处理相反从{@link prototypesCurrentlyInCreation}中移除
14                          */
15                         afterPrototypeCreation(beanName);
16                     }
17                     bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
18                 }

分析:

原型模式下bean的初始化很简单,直接创建一个新Bean实例就可以了。

  • beforePrototypeCreation:记录加载原型模式bean的加载状态,前置处理。
  • createBean创建实例对象,该方法非常重要,后续会详细进行分析。
  • afterPrototypeCreation:移除创建时添加的标志,后置处理与beforePrototypeCreation方法功能相反。
  • 最后调用getObjectForBeanInstance获取实例,该方法在【spring源码分析】IOC容器初始化(六)中已经分析,这里不再赘述。

AbstractBeanFactory#beforePrototypeCreation

 1    /**
 2      * 原型模式下存储beanName的ThreadLocal<br/>
 3      * Names of beans that are currently in creation.
 4      */
 5 private final ThreadLocal<Object> prototypesCurrentlyInCreation =
 6             new NamedThreadLocal<>("Prototype beans currently in creation");
 7 
 8 protected void beforePrototypeCreation(String beanName) {
 9         // 从ThreadLocal中取出对象
10         Object curVal = this.prototypesCurrentlyInCreation.get();
11         if (curVal == null) {
12             // 如果为空,则设置值
13             this.prototypesCurrentlyInCreation.set(beanName);
14         } else if (curVal instanceof String) {
15             // 如果curVal为String类型,则进行添加
16             Set<String> beanNameSet = new HashSet<>(2);
17             beanNameSet.add((String) curVal);
18             beanNameSet.add(beanName);
19             this.prototypesCurrentlyInCreation.set(beanNameSet);
20         } else {
21             // 否则将curVal转换成set集合,添加beanName
22             Set<String> beanNameSet = (Set<String>) curVal;
23             beanNameSet.add(beanName);
24         }
25     }

分析:

这里的前置处理就是将beanName加入ThreadLocal中,逻辑简单。

AbstractBeanFactory#afterPrototypeCreation

 1     protected void afterPrototypeCreation(String beanName) {
 2         Object curVal = this.prototypesCurrentlyInCreation.get();
 3         if (curVal instanceof String) {
 4             this.prototypesCurrentlyInCreation.remove();
 5         } else if (curVal instanceof Set) {
 6             Set<String> beanNameSet = (Set<String>) curVal;
 7             beanNameSet.remove(beanName);
 8             if (beanNameSet.isEmpty()) {
 9                 this.prototypesCurrentlyInCreation.remove();
10             }
11         }
12     }

分析:

后置处理与前置处理beforePrototypeCreation正好相反,将标记从ThreadLocal中移除。

#3.其他作用域

 1 // 获得scopeName对应的Scope对象
 2                     String scopeName = mbd.getScope();
 3                     final Scope scope = this.scopes.get(scopeName);
 4                     if (scope == null) {
 5                         throw new IllegalStateException("No Scope registered for scope name ‘" + scopeName + "‘");
 6                     }
 7                     try {
 8                         /**
 9                          * 从指定的scope下创建bean
10                          * {@link SimpleThreadScope#get方法}
11                          */
12                         Object scopedInstance = scope.get(beanName, () -> {
13                             beforePrototypeCreation(beanName);
14                             try {
15                                 return createBean(beanName, mbd, args);
16                             } finally {
17                                 afterPrototypeCreation(beanName);
18                             }
19                         });
20                         bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
21                     } catch (IllegalStateException ex) {
22                         throw new BeanCreationException(beanName,
23                                                         "Scope ‘" + scopeName + "‘ is not active for the current thread; consider " +
24                                                                 "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
25                                                         ex);
26                     }
27                 }
28             } catch (BeansException ex) {
29                 cleanupAfterBeanCreationFailure(beanName);
30                 throw ex;
31             }

分析:

其他作用域bean的创建过程与原型模式的流程一样,只是获取bean的方式变成了Scope#get(String name,ObjectFactory<?> objectFactory)。

 1 //  SimpleThreadScope
 2 public Object get(String name, ObjectFactory<?> objectFactory) {
 3         // 获取scope缓存
 4         Map<String, Object> scope = this.threadScope.get();
 5         Object scopedObject = scope.get(name);
 6         if (scopedObject == null) {
 7             // 这里getObject也是进行方法回调
 8             scopedObject = objectFactory.getObject();
 9             // 加入缓存
10             scope.put(name, scopedObject);
11         }
12         return scopedObject;
13     }

这里仅仅是Scope接口的一种实现,该接口还有其他多种实现,其具体源码可查看相应实现类:

分享图片

至此,Bean加载的大致流程已分析完毕,当然本篇文章并未分析一个很重要的函数createBean,该函数留在后续的文章继续分析。


by Shawn Chen,2019.04.22,下午。

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