Spring，IOC源码分析
有错勿喷
1.首先是Spring，IOC的基本概念
- IOC是一个容器
- 容器启动的时候创建所有单实例对象
- 我们可以直接从容器中获取到这个对象
2.调试流程
- ioc容器的启动过程?启动期间都做了什么(什么时候创建所有单实例bean )
- ioc是如何创建这些单实例bean ,并如何管理的;到底保存在了那里?
3.我们首先观察对象是什么时候创建的
- 我们可以先写一个实体类Person，并且写一个无参及有参构造器，并写上输出语句，这样我们就可以在创建Person对象的时候观察到
public class Person {
private String name;
public Person() {
System.out.println("person构造");
}
getset方法。。。
toString方法。。。
- 在容器中配置,创建一个Spring的配置文件
<bean id="person01" class="com.xj.bean.Person">
<property name="name" value="xj"></property>
</bean>
4.接下来就可以开始我们的调试啦
1. 首先对于Spring，使用以下代码创建对象
ApplicationContext ioc = new ClassPathXMLApplicationContext("ioc.xml");
2. 进入创建ioc容器对象
ClassPathXMLApplicationContext.java中，调用另一个构造器
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
3. 在这个里当我们执行完refresh()方法后，可以观察到控制台打印了Person的构造器，我们可以知道，组件的创建在refresh中，所以我们进入refresh中
refresh();
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
4. finishBeanFactoryInitialization(beanFactory);
AbstractApplicationContext.java中，我们可以观察到在
finishBeanFactoryInitialization(beanFactory);之后会打印，我们再进入
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
prepareRefresh();
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
prepareBeanFactory(beanFactory);
try {
postProcessBeanFactory(beanFactory);
invokeBeanFactoryPostProcessors(beanFactory);
registerBeanPostProcessors(beanFactory);
initMessageSource();
initApplicationEventMulticaster();
onRefresh();
registerListeners();
//在这里打印---
**finishBeanFactoryInitialization(beanFactory);**
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
destroyBeans();
cancelRefresh(ex);
throw ex;
}
finally {
resetCommonCaches();
}
}
}
5. beanFactory.preInstantiateSingletons();
AbstractApplicationContext.java中,我们可以再次观察到最后一句的时候打印
beanFactory.preInstantiateSingletons();,所以我们再进去
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
@Override
public String resolveStringValue(String strVal) {
return getEnvironment().resolvePlaceholders(strVal);
}
});
}
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
beanFactory.setTempClassLoader(null);
beanFactory.freezeConfiguration();
//这里进入
beanFactory.preInstantiateSingletons();
}
6. preInstantiateSingletons();
这里就是我们重头戏的开始了
@Override
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Pre-instantiating singletons in " + this);
}
//拿到所有要创建的bean的名字，也就是我们配置的bean的id，如上面我配置的<bean id="person01" class="com.xj.bean.Person">，也就是这个person01
//如果有多个的话，就person01，person02,person03
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
//按照顺序创建bean
for (String beanName : beanNames) {
//根据bean id 获取到bean的定义信息，如全类名，是否单实例，是否懒加载等等
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//判断bean是单实例，并且不是抽象，不是懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//是否是实现了FactoryBean接口的bean，我们的person不是，所以看下面的else
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
//否则的话，执行getBean，我们进入getBean
else {
getBean(beanName);
}
}
}
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
smartSingleton.afterSingletonsInstantiated();
return null;
}
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
7. getBean();
AbstractBeanFactory.java中
getBean方法内部调用doGetBean()方法，我们再次进入
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
8. doGetBean(name, null, null, false);
@SuppressWarnings("unchecked")
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
//先从已经注册的所有单实例bean中看有没有这个bean，第一次创建肯定是没有的,所以执行下面的else
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
String nameToLookup = originalBeanName(name);
if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
//拿到创建当前bean之前需要提前创建（依赖）的bean，dependsOn，如果有就循环创建
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
//这边再次调用getBean创建
getBean(dep);
}
}
//这里就是真正的创建bean实例
if (mbd.isSingleton()) {
//调用getSingleton创建bean，见9
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
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()) {
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
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, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
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;
}
}
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
9. getSingleton(beanName, new ObjectFactor。。。
从容器中取的名字为beanName的对象，如果不存在就创建，否则就直接从容器中拿
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
//先从一个地方将bean get出来
//这个singletonObjects就是一个map，里面保存所有的单实例对象，也就是我们的容器
//如果容器中有的话，就不会创建
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<Exception>();
}
try {
//bean创建，利用反射创建对象
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
//将刚创建好的bean添加到singletonObjects中
addSingleton(beanName, singletonObject);
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
4. ioc实质
我们刚才已经看到了一个ioc容器
singletonObjects：
缓存所有单实例的对象，对象名->对象实例
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);
IOC容器之一：保存单实例bean的地方；
IOC就是众多map的集合
本博客文章主要供博主学习交流用，所有描述、代码无法保证准确性，如有问题可以留言共同讨论。
