作者:shihuaping0918@163.com转载请注明作者
scope是用来定义spring如何创建bean的。bean默认是singleton，在容器中只有一个实例，名字就提示了，是设计模式里的单件，或者叫单例。还有一种是prototype，可以创建多个实例。对于singleton，无所谓生命周期，反正容器在它就在，顶多是关注一下它是在哪里实例化的。只有prototype类型的才有真正意义上的生命周期。这篇文章就带大家来看一下prototype类型的bean的生命周期。
prototype类型的bean可以通过应用上下文获取时创建，也可以在注入时创建。先看一下应用上下文获取时，它是怎么创建的。因为它有方法作为入口，看起来比较直观。在之前的文章中，其实已经分析过应用上下文相关的代码了，也就是applicationContext相关的代码，其中有一个类对register factory的方法做了一层封装，用意就是在调register factory方法时，先做一下判断。下面直接去AbstractApplicationContext里看方法。
@Override
public Object getBean(String name) throws BeansException { //看它就好了
assertBeanFactoryActive(); //同下
return getBeanFactory().getBean(name);
}
@Override
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
assertBeanFactoryActive(); //同上
return getBeanFactory().getBean(name, requiredType);
}
@Override
public Object getBean(String name, Object... args) throws BeansException {
assertBeanFactoryActive(); //同上
return getBeanFactory().getBean(name, args);
}
@Override
public <T> T getBean(Class<T> requiredType) throws BeansException {
assertBeanFactoryActive(); //同上
return getBeanFactory().getBean(requiredType);
}
@Override
public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException {
assertBeanFactoryActive(); //同上
return getBeanFactory().getBean(requiredType, args);
}
前面的文章里介绍过getBeanFactory获取的是DefaultListableBeanFactory，到这个类里去找getBean方法，getBean位于AbstractBeanFactory里面。
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
注意参数，要关注参数值，后续的代码看起来才有重点。
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//requiredType=null,args=null,typeCheckOnly=false，注意参数
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) { //我们要看的是prototype,single这一段跳过
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else { //代码进了这里，非singleton的类型
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
//如果有父类厂，且当前类厂中没有这个bean，就到父类厂中查找，不进这个条件里面
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) { //args==null，不进
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) { //requiredType==null，不进
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) { //注意进来的参数typeCheckOnly==false
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) { //创建父类，属性成员类，等等
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) { //循环依赖，抛异常
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) { //singleton类型跳过
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) { //我们想要的prototype代码流程，直接创建一个新的bean
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName); //tls中添加当前创建的bean信息
prototypeInstance = createBean(beanName, mbd, args); //在这里创建了bean
}
finally {
afterPrototypeCreation(beanName); //tls中清除当前创建的bean信息
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else { // session/request类型
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
在createBrean中，会实例化bean，并且初始化，填充好bean的成员属性，详细分析见《spring源码分析6----bean字段or成员变量填充》，这篇已经对bean的实例化做了详细的分析。prototype的bean使用完以后，会由垃圾回收对它进行处理。
上面讲的是getBean显式获取bean，下面讲注入的时候，prototyp类型的bean是怎么处理的。要接着上面的createBean继续分析，实例化以后就是成员的填充，这里就会用到注入了。
在前面分析bean实例化的时候已经涉及到类初始化，成员的填充，这里只是前面文章内容的延伸。createBean调用doCreateBean。而doCreateBean会调用populateBean，填充bean。
/**
* Populate the bean instance in the given BeanWrapper with the property values
* from the bean definition.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param bw the BeanWrapper with bean instance
*/
@SuppressWarnings("deprecation") // for postProcessPropertyValues
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) { //实例为null
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { //做一些预处理
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null); //获取属性
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs); //按名称注入
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs); //按类型注入，看类型吧，比较快
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
applyPropertyValues(beanName, mbd, bw, pvs); //填充在这里完成
}
}
去看autowireByType
/**
* Abstract method defining "autowire by type" (bean properties by type) behavior.
* <p>This is like PicoContainer default, in which there must be exactly one bean
* of the property type in the bean factory. This makes bean factories simple to
* configure for small namespaces, but doesn't work as well as standard Spring
* behavior for bigger applications.
* @param beanName the name of the bean to autowire by type
* @param mbd the merged bean definition to update through autowiring
* @param bw the BeanWrapper from which we can obtain information about the bean
* @param pvs the PropertyValues to register wired objects with
*/
protected void autowireByType(
String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (String propertyName : propertyNames) {
try {
PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
// Don't try autowiring by type for type Object: never makes sense,
// even if it technically is a unsatisfied, non-simple property.
if (Object.class != pd.getPropertyType()) {
MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
// Do not allow eager init for type matching in case of a prioritized post-processor.
boolean eager = !(bw.getWrappedInstance() instanceof PriorityOrdered);
DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter); //查找属性对应的依赖
if (autowiredArgument != null) {
pvs.add(propertyName, autowiredArgument);
}
for (String autowiredBeanName : autowiredBeanNames) {
registerDependentBean(autowiredBeanName, beanName);
if (logger.isTraceEnabled()) {
logger.trace("Autowiring by type from bean name '" + beanName + "' via property '" +
propertyName + "' to bean named '" + autowiredBeanName + "'");
}
}
autowiredBeanNames.clear();
}
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
}
}
}
这个方法当中，resolveDependency会调用doResolveDependency。
@Nullable
public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
try {
Object shortcut = descriptor.resolveShortcut(this);
if (shortcut != null) {
return shortcut;
}
Class<?> type = descriptor.getDependencyType();
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) { //我们要看创建过程，这里跳过
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()));
}
}
Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
if (multipleBeans != null) {
return multipleBeans;
}
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (isRequired(descriptor)) {
raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
}
return null;
}
String autowiredBeanName;
Object instanceCandidate;
if (matchingBeans.size() > 1) { //匹配到多个，这里不用看
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 { //精准匹配到一个
// We have exactly one match.
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) { //如果匹配到的是类，这里我们要关注
instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this); //就是在这里实例化的
}
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);
}
}
在doresolveDependency方法中，对于prototype的bean，会去创建一个实例，看一看descriptor.resolveCondidate
/**
* Resolve the specified bean name, as a candidate result of the matching
* algorithm for this dependency, to a bean instance from the given factory.
* <p>The default implementation calls {@link BeanFactory#getBean(String)}.
* Subclasses may provide additional arguments or other customizations.
* @param beanName the bean name, as a candidate result for this dependency
* @param requiredType the expected type of the bean (as an assertion)
* @param beanFactory the associated factory
* @return the bean instance (never {@code null})
* @throws BeansException if the bean could not be obtained
* @since 4.3.2
* @see BeanFactory#getBean(String)
*/
public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
throws BeansException {
return beanFactory.getBean(beanName); //这就是文章一开始分析的方法
}
总结一下，populateBean填充bean实例的属性，它先调用autowireByType获取属性的名称，还有属性要填充的值，在本篇中，这个值指的就是被prototype修饰的bean。这个值是通过getBean(name)来获取的，而文章前面分析过getBean(name)对于prototype修饰的bean，是直接创建一个实例。从代码来看，在自动注入的情况下，prototype修饰的bean总是会被重新创建。
写在最后：接单，有后台活java/cpp/lua/go联系shihuaping0918@163.com。不上班了也要有点收入才行。
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