原型Bean加载过程
之前的文章，分析了非懒加载的单例Bean整个加载过程，除了非懒加载的单例Bean之外，Spring中还有一种Bean就是原型（Prototype）的Bean，看一下定义方式：
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加载流程总得来说和单例Bean差不多，看一下不同之处，在AbstractBeanFactory的doGetBean的方法的这一步：
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是一样的，原型Bean实例化的主要区别就在于第6行，它是直接创建bean的，而单例bean我们再对比一下：
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 }
它优先会尝试getSington，即先尝试从singletonObjects中获取一下bean是否存在，如果存在直接返回singletonObjects中的bean对象。
接着，我们看到原型bean创建和单例bean创建的区别还在于第5行和第9行，先看第5行的代码：
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 }
这段主要是说bean在创建前要把当前beanName设置到ThreadLocal中去，其目的是保证多线程不会同时创建同一个bean。接着看第9行的代码实现，即bean创建之后做了什么：
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，就是把当前bean移除一下，这样其它线程就可以创建bean了。第11行的代码不看了，意思是如果bean是FactoryBean的实现类的话，调用getObject()方法获取真正的对象。
byName源码实现
Spring有为开发者提供Autowire（自动装配）的功能，自动装配最常用的就是byName和byType这两种属性。由于自动装配是为了解决对象注入导致的<property>过多的问题，因此很容易找到byName与byType的Spring源码实现应该在属性注入这一块，定位到属性注入的代码AbstractAutowireCapableBeanFactory的populateBean方法，直接截取重点：
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行判断是否byName形式，是就执行byName自动装配代码；第11行~第13行判断是否byType形式，是就执行byType自动装配代码。那么首先看一下第7行的byName代码实现：
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 }
篇幅问题，代码不一层层跟了，逻辑梳理一下：
- 第4行，找到Bean中不是简单属性的属性，这句话有点绕，意思就是找到属性是对象类型的属性，但也不是所有的对象类型都会被找到，比如CharSequence类型、Number类型、Date类型、URL类型、URI类型、Locale类型、Class类型就会忽略，具体可见BeanUtils的isSimpleProperty方法
- 第5行~第7行，遍历所有被找到的属性，如果bean定义中包含了属性名，那么先实例化该属性名对应的bean
- 第9行registerDependentBean，注册一下当前bean的依赖bean，用于在某个bean被销毁前先将其依赖的bean销毁
其余代码都是一些打日志的，没什么好说的。
byType源码实现
上面说了byName的源码实现，接下来看一下byType源码实现：
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 }
前面一样，到第10行都是找到Bean中属性是对象类型的属性。
接着就是遍历一下PropertyName，获取PropertyName对应的属性描述，注意一下16行的判断及其对应的注释：不要尝试自动装配Object类型，这没有任何意义，即使从技术角度看它是一个非简单的对象属性。
第18行~第20行跳过（没有太明白是干什么的），byType实现的源码主要在第21行的方法resolveDependency中，这个方法是AbstractAutowireCapableBeanFactory类的实现类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 }
这里判断一下要自动装配的属性是ObjectFactory.class还是javaxInjectProviderClass还是其他的，我们装配的是其他的，看一下12行的代码实现：
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 }
第四行结果是null不看了，为了简化代码Array装配、Collection装配、Map装配的代码都略去了，重点看一下普通属性的装配。首先是第25行获取一下自动装配的候选者：
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 }
代码逻辑整理一下：
- 首先获取候选者bean名称，通过DefaultListableBeanFactory的getBeanNamesForType方法，即找一下所有的Bean定义中指定Type的实现类或者子类
- 接着第7行~第16行的判断要自动装配的类型是不是要自动装配的纠正类型，这个在【Spring源码分析】非懒加载的单例Bean初始化前后的一些操作一文讲PrepareBeanFactory方法的时候有讲过，如果要自动装配的类型是纠正类型，比如是一个ResourceLoader，那么就会为该类型生成一个代理实例，具体可以看一下第10行的AutowireUtils.resolveAutowiringValue方法的实现
- 正常来说都是执行的第17行~第21行的代码，逐个判断查找一下beanName对应的BeanDefinition，判断一下是不是自动装配候选者，默认都是的，如果<bean>的autowire-candidate属性设置为false就不是
这样，拿到所有待装配对象的实现类或者子类的候选者，组成一个Map，Key为beanName，Value为具体的Bean。接着回看获取Bean之后的逻辑：
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 }
整理一下逻辑：
- 如果拿到的Map是空的且属性必须注入，抛异常
- 如果拿到的Map中有多个候选对象，判断其中是否有<bean>中属性配置为"primary=true"的，有就拿执行第13行~第15行的代码，没有就第8行的方法返回null，抛异常，这个异常的描述相信Spring用的比较多的应该比较熟悉
- 如果拿到的Map中只有一个候选对象，直接拿到那个
通过这样一整个流程，实现了byType自动装配，byType自动装配流程比较长，中间细节比较多，还需要多看看才能弄明白。
最后注意一点，即所有待注入的PropertyName-->PropertyValue映射拿到之后都只是放在MutablePropertyValues中，最后由AbstractPropertyAccessor类的setPropertyValues方法遍历并进行逐一注入。
通过FactoryBean获取Bean实例源码实现
我们知道可以通过实现FactoryBean接口，重写getObject()方法实现个性化定制Bean的过程，这部分我们就来看一下Spring源码是如何实现通过FactoryBean获取Bean实例的。代码直接定位到AbstractBeanFactory的doGetBean方法创建单例Bean这部分：
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首先是个Bean且被实例化出来成为一个对象之后才能调用getObject()方法，因此还是会执行第3行~第16行的代码，这段代码之前分析过了就不说了。之后执行第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行判断一下是否beanName以"&"开头并且不是FactoryBean的实现类，不满足则抛异常，因为beanName以"&"开头是FactoryBean的实现类bean定义的一个特征。
接着判断第12行~第14行，如果：
- bean不是FactoryBean的实现类
- beanName以"&"开头
这两种情况，都直接把生成的bean对象返回出去，不会执行余下的流程。
最后流程走到第16行~第30行，最终调用getObject()方法实现个性化定制bean，先执行第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行的代码与第12行~第13行的代码最终都是一样的，调用了如下一段：
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行的代码，都一样，最终调用getObject()方法获取对象。回过头去看之前的getObjectFromFactoryBean方法，虽然if...else...逻辑最终都是调用了以上的方法，但是区别在于：
- 如果FactoryBean接口实现类的isSington方法返回的是true，那么每次调用getObject方法的时候会优先尝试从FactoryBean对象缓存中取目标对象，有就直接拿，没有就创建并放入FactoryBean对象缓存，这样保证了每次单例的FactoryBean调用getObject()方法后最终拿到的目标对象一定是单例的，即在内存中都是同一份
- 如果FactoryBean接口实现类的isSington方法返回的是false，那么每次调用getObject方法的时候都会新创建一个目标对象
时间： 2024-08-02 05:57:20