原型Bean加載過程
之前的文章,分析了非懶加載的單例Bean整個加載過程,除了非懶加載的單例Bean之外,Spring中還有一種Bean就是原型(Prototype)的Bean,看一下定義方式:
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://www.springframework.org/schema/beans 5 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 6 7 <bean id="prototypeBean" class="org.xrq.action.PrototypeBean" scope="prototype" /> 8 9 </beans>
原型Bean加載流程總得來說和單例Bean差不多,看一下不同之處,在AbstractBeanFactory的doGetBean的方法的這一步:
1 else if (mbd.isPrototype()) { 2 // It's a prototype -> create a new instance. 3 Object prototypeInstance = null; 4 try { 5 beforePrototypeCreation(beanName); 6 prototypeInstance = createBean(beanName, mbd, args); 7 } 8 finally { 9 afterPrototypeCreation(beanName); 10 } 11 bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); 12 }
第6行createBean是一樣的,原型Bean實例化的主要區別就在於第6行,它是直接創建bean的,而單例bean我們再對比一下:
1 if (mbd.isSingleton()) { 2 sharedInstance = getSingleton(beanName, new ObjectFactory() { 3 public Object getObject() throws BeansException { 4 try { 5 return createBean(beanName, mbd, args); 6 } 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 destroySingleton(beanName); 12 throw ex; 13 } 14 } 15 }); 16 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 17 }
它優先會嘗試getSington,即先嘗試從singletonObjects中獲取一下bean是否存在,如果存在直接返回singletonObjects中的bean對象。
接著,我們看到原型bean創建和單例bean創建的區別還在於第5行和第9行,先看第5行的代碼:
1 protected void beforePrototypeCreation(String beanName) { 2 Object curVal = this.prototypesCurrentlyInCreation.get(); 3 if (curVal == null) { 4 this.prototypesCurrentlyInCreation.set(beanName); 5 } 6 else if (curVal instanceof String) { 7 Set<String> beanNameSet = new HashSet<String>(2); 8 beanNameSet.add((String) curVal); 9 beanNameSet.add(beanName); 10 this.prototypesCurrentlyInCreation.set(beanNameSet); 11 } 12 else { 13 Set<String> beanNameSet = (Set<String>) curVal; 14 beanNameSet.add(beanName); 15 } 16 }
這段主要是說bean在創建前要把當前beanName設置到ThreadLocal中去,其目的是保證多線程不會同時創建同一個bean。接著看第9行的代碼實現,即bean創建之後做了什麼:
1 protected void afterPrototypeCreation(String beanName) { 2 Object curVal = this.prototypesCurrentlyInCreation.get(); 3 if (curVal instanceof String) { 4 this.prototypesCurrentlyInCreation.remove(); 5 } 6 else if (curVal instanceof Set) { 7 Set<String> beanNameSet = (Set<String>) curVal; 8 beanNameSet.remove(beanName); 9 if (beanNameSet.isEmpty()) { 10 this.prototypesCurrentlyInCreation.remove(); 11 } 12 } 13 }
很好理解,就是把當前bean移除一下,這樣其它線程就可以創建bean了。第11行的代碼不看了,意思是如果bean是FactoryBean的實現類的話,調用getObject()方法獲取真正的對象。
byName源碼實現
Spring有為開發者提供Autowire(自動裝配)的功能,自動裝配最常用的就是byName和byType這兩種屬性。由於自動裝配是為了解決對象注入導致的<property>過多的問題,因此很容易找到byName與byType的Spring源碼實現應該在屬性注入這一塊,定位到屬性注入的代碼AbstractAutowireCapableBeanFactory的populateBean方法,直接截取重點:
1 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME || 2 mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { 3 MutablePropertyValues newPvs = new MutablePropertyValues(pvs); 4 5 // Add property values based on autowire by name if applicable. 6 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { 7 autowireByName(beanName, mbd, bw, newPvs); 8 } 9 10 // Add property values based on autowire by type if applicable. 11 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { 12 autowireByType(beanName, mbd, bw, newPvs); 13 } 14 15 pvs = newPvs; 16 }
看到第6行~第8行判斷是否byName形式,是就執行byName自動裝配代碼;第11行~第13行判斷是否byType形式,是就執行byType自動裝配代碼。那麼首先看一下第7行的byName代碼實現:
1 protected void autowireByName( 2 String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) { 3 4 String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw); 5 for (String propertyName : propertyNames) { 6 if (containsBean(propertyName)) { 7 Object bean = getBean(propertyName); 8 pvs.add(propertyName, bean); 9 registerDependentBean(propertyName, beanName); 10 if (logger.isDebugEnabled()) { 11 logger.debug("Added autowiring by name from bean name '" + beanName + 12 "' via property '" + propertyName + "' to bean named '" + propertyName + "'"); 13 } 14 } 15 else { 16 if (logger.isTraceEnabled()) { 17 logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName + 18 "' by name: no matching bean found"); 19 } 20 } 21 } 22 }
篇幅問題,代碼不一層層跟了,邏輯梳理一下:
其余代碼都是一些打日志的,沒什麼好說的。
byType源碼實現
上面說了byName的源碼實現,接下來看一下byType源碼實現:
1 protected void autowireByType( 2 String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) { 3 4 TypeConverter converter = getCustomTypeConverter(); 5 if (converter == null) { 6 converter = bw; 7 } 8 9 Set<String> autowiredBeanNames = new LinkedHashSet<String>(4); 10 String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw); 11 for (String propertyName : propertyNames) { 12 try { 13 PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName); 14 // Don't try autowiring by type for type Object: never makes sense, 15 // even if it technically is a unsatisfied, non-simple property. 16 if (!Object.class.equals(pd.getPropertyType())) { 17 MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd); 18 // Do not allow eager init for type matching in case of a prioritized post-processor. 19 boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass()); 20 DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager); 21 Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter); 22 if (autowiredArgument != null) { 23 pvs.add(propertyName, autowiredArgument); 24 } 25 for (String autowiredBeanName : autowiredBeanNames) { 26 registerDependentBean(autowiredBeanName, beanName); 27 if (logger.isDebugEnabled()) { 28 logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" + 29 propertyName + "' to bean named '" + autowiredBeanName + "'"); 30 } 31 } 32 autowiredBeanNames.clear(); 33 } 34 } 35 catch (BeansException ex) { 36 throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex); 37 } 38 } 39 }
前面一樣,到第10行都是找到Bean中屬性是對象類型的屬性。
接著就是遍歷一下PropertyName,獲取PropertyName對應的屬性描述,注意一下16行的判斷及其對應的注釋:不要嘗試自動裝配Object類型,這沒有任何意義,即使從技術角度看它是一個非簡單的對象屬性。
第18行~第20行跳過(沒有太明白是干什麼的),byType實現的源碼主要在第21行的方法resolveDependency中,這個方法是AbstractAutowireCapableBeanFactory類的實現類DefaultListableBeanFactory中的方法:
1 public Object resolveDependency(DependencyDescriptor descriptor, String beanName, 2 Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException { 3 4 descriptor.initParameterNameDiscovery(getParameterNameDiscoverer()); 5 if (descriptor.getDependencyType().equals(ObjectFactory.class)) { 6 return new DependencyObjectFactory(descriptor, beanName); 7 } 8 else if (descriptor.getDependencyType().equals(javaxInjectProviderClass)) { 9 return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName); 10 } 11 else { 12 return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter); 13 } 14 }
這裡判斷一下要自動裝配的屬性是ObjectFactory.class還是javaxInjectProviderClass還是其他的,我們裝配的是其他的,看一下12行的代碼實現:
1 protected Object doResolveDependency(DependencyDescriptor descriptor, Class<?> type, String beanName, 2 Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException { 3 4 Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor); 5 if (value != null) { 6 if (value instanceof String) { 7 String strVal = resolveEmbeddedValue((String) value); 8 BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null); 9 value = evaluateBeanDefinitionString(strVal, bd); 10 } 11 TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter()); 12 return converter.convertIfNecessary(value, type); 13 } 14 15 if (type.isArray()) { 16 ... 17 } 18 else if (Collection.class.isAssignableFrom(type) && type.isInterface()) { 19 ... 20 } 21 else if (Map.class.isAssignableFrom(type) && type.isInterface()) { 22 ... 23 } 24 else { 25 Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor); 26 if (matchingBeans.isEmpty()) { 27 if (descriptor.isRequired()) { 28 raiseNoSuchBeanDefinitionException(type, "", descriptor); 29 } 30 return null; 31 } 32 if (matchingBeans.size() > 1) { 33 String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor); 34 if (primaryBeanName == null) { 35 throw new NoSuchBeanDefinitionException(type, "expected single matching bean but found " + 36 matchingBeans.size() + ": " + matchingBeans.keySet()); 37 } 38 if (autowiredBeanNames != null) { 39 autowiredBeanNames.add(primaryBeanName); 40 } 41 return matchingBeans.get(primaryBeanName); 42 } 43 // We have exactly one match. 44 Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next(); 45 if (autowiredBeanNames != null) { 46 autowiredBeanNames.add(entry.getKey()); 47 } 48 return entry.getValue(); 49 } 50 }
第四行結果是null不看了,為了簡化代碼Array裝配、Collection裝配、Map裝配的代碼都略去了,重點看一下普通屬性的裝配。首先是第25行獲取一下自動裝配的候選者:
1 protected Map<String, Object> findAutowireCandidates( 2 String beanName, Class requiredType, DependencyDescriptor descriptor) { 3 4 String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors( 5 this, requiredType, true, descriptor.isEager()); 6 Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length); 7 for (Class autowiringType : this.resolvableDependencies.keySet()) { 8 if (autowiringType.isAssignableFrom(requiredType)) { 9 Object autowiringValue = this.resolvableDependencies.get(autowiringType); 10 autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType); 11 if (requiredType.isInstance(autowiringValue)) { 12 result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue); 13 break; 14 } 15 } 16 } 17 for (String candidateName : candidateNames) { 18 if (!candidateName.equals(beanName) && isAutowireCandidate(candidateName, descriptor)) { 19 result.put(candidateName, getBean(candidateName)); 20 } 21 } 22 return result; 23 }
代碼邏輯整理一下:
這樣,拿到所有待裝配對象的實現類或者子類的候選者,組成一個Map,Key為beanName,Value為具體的Bean。接著回看獲取Bean之後的邏輯:
1 Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor); 2 if (matchingBeans.isEmpty()) { 3 if (descriptor.isRequired()) { 4 raiseNoSuchBeanDefinitionException(type, "", descriptor); 5 } 6 return null; 7 } 8 if (matchingBeans.size() > 1) { 9 String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor); 10 if (primaryBeanName == null) { 11 throw new NoSuchBeanDefinitionException(type, "expected single matching bean but found " + 12 matchingBeans.size() + ": " + matchingBeans.keySet()); 13 } 14 if (autowiredBeanNames != null) { 15 autowiredBeanNames.add(primaryBeanName); 16 } 17 return matchingBeans.get(primaryBeanName); 18 } 19 // We have exactly one match. 20 Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next(); 21 if (autowiredBeanNames != null) { 22 autowiredBeanNames.add(entry.getKey()); 23 } 24 ... 25 }
整理一下邏輯:
通過這樣一整個流程,實現了byType自動裝配,byType自動裝配流程比較長,中間細節比較多,還需要多看看才能弄明白。
最後注意一點,即所有待注入的PropertyName-->PropertyValue映射拿到之後都只是放在MutablePropertyValues中,最後由AbstractPropertyAccessor類的setPropertyValues方法遍歷並進行逐一注入。
通過FactoryBean獲取Bean實例源碼實現
我們知道可以通過實現FactoryBean接口,重寫getObject()方法實現個性化定制Bean的過程,這部分我們就來看一下Spring源碼是如何實現通過FactoryBean獲取Bean實例的。代碼直接定位到AbstractBeanFactory的doGetBean方法創建單例Bean這部分:
1 // Create bean instance. 2 if (mbd.isSingleton()) { 3 sharedInstance = getSingleton(beanName, new ObjectFactory() { 4 public Object getObject() throws BeansException { 5 try { 6 return createBean(beanName, mbd, args); 7 } 8 catch (BeansException ex) { 9 // Explicitly remove instance from singleton cache: It might have been put there 10 // eagerly by the creation process, to allow for circular reference resolution. 11 // Also remove any beans that received a temporary reference to the bean. 12 destroySingleton(beanName); 13 throw ex; 14 } 15 } 16 }); 17 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 18 }
FactoryBean首先是個Bean且被實例化出來成為一個對象之後才能調用getObject()方法,因此還是會執行第3行~第16行的代碼,這段代碼之前分析過了就不說了。之後執行第17行的方法:
1 protected Object getObjectForBeanInstance( 2 Object beanInstance, String name, String beanName, RootBeanDefinition mbd) { 3 4 // Don't let calling code try to dereference the factory if the bean isn't a factory. 5 if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) { 6 throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass()); 7 } 8 9 // Now we have the bean instance, which may be a normal bean or a FactoryBean. 10 // If it's a FactoryBean, we use it to create a bean instance, unless the 11 // caller actually wants a reference to the factory. 12 if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) { 13 return beanInstance; 14 } 15 16 Object object = null; 17 if (mbd == null) { 18 object = getCachedObjectForFactoryBean(beanName); 19 } 20 if (object == null) { 21 // Return bean instance from factory. 22 FactoryBean factory = (FactoryBean) beanInstance; 23 // Caches object obtained from FactoryBean if it is a singleton. 24 if (mbd == null && containsBeanDefinition(beanName)) { 25 mbd = getMergedLocalBeanDefinition(beanName); 26 } 27 boolean synthetic = (mbd != null && mbd.isSynthetic()); 28 object = getObjectFromFactoryBean(factory, beanName, !synthetic); 29 } 30 return object; 31 }
首先第5行~第7行判斷一下是否beanName以"&"開頭並且不是FactoryBean的實現類,不滿足則拋異常,因為beanName以"&"開頭是FactoryBean的實現類bean定義的一個特征。
接著判斷第12行~第14行,如果:
這兩種情況,都直接把生成的bean對象返回出去,不會執行余下的流程。
最後流程走到第16行~第30行,最終調用getObject()方法實現個性化定制bean,先執行第28行的方法:
1 protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) { 2 if (factory.isSingleton() && containsSingleton(beanName)) { 3 synchronized (getSingletonMutex()) { 4 Object object = this.factoryBeanObjectCache.get(beanName); 5 if (object == null) { 6 object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess); 7 this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT)); 8 } 9 return (object != NULL_OBJECT ? object : null); 10 } 11 } 12 else { 13 return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess); 14 } 15 }
第1行~第11行的代碼與第12行~第13行的代碼最終都是一樣的,調用了如下一段:
1 private Object doGetObjectFromFactoryBean( 2 final FactoryBean factory, final String beanName, final boolean shouldPostProcess) 3 throws BeanCreationException { 4 5 Object object; 6 try { 7 if (System.getSecurityManager() != null) { 8 AccessControlContext acc = getAccessControlContext(); 9 try { 10 object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { 11 public Object run() throws Exception { 12 return factory.getObject(); 13 } 14 }, acc); 15 } 16 catch (PrivilegedActionException pae) { 17 throw pae.getException(); 18 } 19 } 20 else { 21 object = factory.getObject(); 22 } 23 } 24 catch (FactoryBeanNotInitializedException ex) { 25 throw new BeanCurrentlyInCreationException(beanName, ex.toString()); 26 } 27 catch (Throwable ex) { 28 throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex); 29 } 30 31 // Do not accept a null value for a FactoryBean that's not fully 32 // initialized yet: Many FactoryBeans just return null then. 33 if (object == null && isSingletonCurrentlyInCreation(beanName)) { 34 throw new BeanCurrentlyInCreationException( 35 beanName, "FactoryBean which is currently in creation returned null from getObject"); 36 } 37 38 if (object != null && shouldPostProcess) { 39 try { 40 object = postProcessObjectFromFactoryBean(object, beanName); 41 } 42 catch (Throwable ex) { 43 throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex); 44 } 45 } 46 47 return object; 48 }
第12行和第21行的代碼,都一樣,最終調用getObject()方法獲取對象。回過頭去看之前的getObjectFromFactoryBean方法,雖然if...else...邏輯最終都是調用了以上的方法,但是區別在於: