Spring,IOC原始碼分析
阿新 • • 發佈:2020-09-11
有錯勿噴
1.首先是Spring,IOC的基本概念
- IOC是一個容器
- 容器啟動的時候建立所有單例項物件
- 我們可以直接從容器中獲取到這個物件
2.除錯流程
- ioc容器的啟動過程?啟動期間都做了什麼(什麼時候建立所有單例項bean )
- ioc是如何建立這些單例項bean ,並如何管理的;到底儲存在了那裡?
3.我們首先觀察物件是什麼時候建立的
- 我們可以先寫一個實體類Person,並且寫一個無參及有參構造器,並寫上輸出語句,這樣我們就可以在建立Person物件的時候觀察到
public class Person { private String name; public Person() { System.out.println("person構造"); } getset方法。。。 toString方法。。。
- 在容器中配置,建立一個Spring的配置檔案
<bean id="person01" class="com.xj.bean.Person">
<property name="name" value="xj"></property>
</bean>
4.接下來就可以開始我們的除錯啦
1. 首先對於Spring,使用以下程式碼建立物件
ApplicationContext ioc = new ClassPathXMLApplicationContext("ioc.xml");
2. 進入建立ioc容器物件
ClassPathXMLApplicationContext.java中,呼叫另一個構造器
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
3. 在這個裡當我們執行完refresh()方法後,可以觀察到控制檯列印了Person的構造器,我們可以知道,元件的建立在refresh中,所以我們進入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,我們可以觀察到在
finishBeanFactoryInitialization(beanFactory);
之後會列印,我們再進入
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();
//在這裡列印---
**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,我們可以再次觀察到最後一句的時候列印
beanFactory.preInstantiateSingletons();
,所以我們再進去
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();
//這裡進入
beanFactory.preInstantiateSingletons();
}
6. preInstantiateSingletons();
這裡就是我們重頭戲的開始了
@Override
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Pre-instantiating singletons in " + this);
}
//拿到所有要建立的bean的名字,也就是我們配置的bean的id,如上面我配置的<bean id="person01" class="com.xj.bean.Person">,也就是這個person01
//如果有多個的話,就person01,person02,person03
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
//按照順序建立bean
for (String beanName : beanNames) {
//根據bean id 獲取到bean的定義資訊,如全類名,是否單例項,是否懶載入等等
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//判斷bean是單例項,並且不是抽象,不是懶載入
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//是否是實現了FactoryBean介面的bean,我們的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);
}
}
//否則的話,執行getBean,我們進入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方法內部呼叫doGetBean()方法,我們再次進入
@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;
//先從已經註冊的所有單例項bean中看有沒有這個bean,第一次建立肯定是沒有的,所以執行下面的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);
//拿到建立當前bean之前需要提前建立(依賴)的bean,dependsOn,如果有就迴圈建立
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);
//這邊再次呼叫getBean建立
getBean(dep);
}
}
//這裡就是真正的建立bean例項
if (mbd.isSingleton()) {
//呼叫getSingleton建立bean,見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 ObjectFactory
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
//先從一個地方將bean get出來
//這個singletonObjects就是一個map,裡面儲存所有的單例項物件,也就是我們的容器
//如果容器中有的話,就不會建立
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建立,利用反射建立物件
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) {
//將剛建立好的bean新增到singletonObjects中
addSingleton(beanName, singletonObject);
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
10. ioc實質
我們剛才已經看到了一個ioc容器
singletonObjects:
快取所有單例項的物件,物件名->物件例項
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);
IOC容器之一:儲存單例項bean的地方;
IOC就是眾多map的集合