Spring——IoC
程序员文章站
2022-05-23 10:33:59
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一、精准理解Ioc
用过Spring的程序员，或多或少都知道Spring中Ioc（Inversion of control）的概念，今天我就我在学习Spring Ioc源码分析中对Ioc的理解
Ioc(Inversion of control)控制反转，对于这个它的代号，个人觉得只能代表它功能的一方面，即管理对象的创建，不能很明显的表达出它还能管理对象间依赖关系。所以个人更爱好将“控制反转”+“依赖反转”和起来一起代表Ioc
那么就细节的说下“控制反转”、“依赖反转”这两个名词的概念和这两个概念涉及到的“依赖注入（dependency insect）”
控制反转：为什么要控制反转？谁控制了谁？控制了什么？什么是反转？
为什么要控制反转？：在传统的JavaEE开发中都是应用程序主动去获取所需要的资源（对象居多），这样会在逻辑代码中造成对所依赖的对象的直接依赖（或者说对象会直接管理所依赖对象创建、获取等），造成了代码的高度耦合性，违反了程序开发的“编译不依赖，运行依赖”的原则。所以需要控制反转。
谁控制谁？：当然是Ioc容器管理对象
控制了什么？：Ioc容器控制了对象的创建权，应用程序获取资源的主动权
什么是反转？：当然是由应用程序主动创建依赖对象和主动获取依赖对象反转为了由Ioc容器来管理对象的创建和对所需资源的分发。
依赖反转：其实和控制反转是同一个意思，只是不同的说法而已，可能更能全面的概括Ioc容器的功能（相比“控制反转”）
依赖注入：其实就是Ioc容器实现对所需资源分配的一种实现，即对对象所依赖的资源（对象）进行引用的赋值（当然依赖注入的概念比这个要广，比如对Ioc容器所创建的对象的属性进行赋值也是DI）
二、源码分析
好了，理解了上面的概念可以比较好了对下面的源码分析有好的帮助。在开始分析之前，我还想传达的一个宏观概念就是Ioc容器体系架构和实现思想
Ioc容器体系架构：右BeanFactory（Ioc容器的规范）、ApplicationContext（比较高级的Ioc容器规范）
Ioc容器的设计思想：Ioc容器是将程序员定义的Bean抽象成为自身内部的数据结构（BeanDefinition），即可以理解Bean在Ioc中的内存模型就是BeanDefinition
再者，还要从大体上掌握Ioc初始化的一个整体脉络：定位资源文件、加载解析资源文件、注册BeanDefinition、依赖注入
有了上面的宏观概念下面具体分析的时候就好把握程序的走向了。
具体分析ApplicationContext的实现类FileSystemXmlApplicationContext容器
一、FileSystemXmlApplicationContext源码
//知道XmlApplicationContext是FileSystemXmlApplicationConext的基类（父类）
public class FileSystemXmlApplicationContext extends AbstractXmlApplicationContext {
public FileSystemXmlApplicationContext() {
}
public FileSystemXmlApplicationContext(ApplicationContext parent) {
super(parent);
}
public FileSystemXmlApplicationContext(String configLocation) throws BeansException {
this(new String[]{configLocation}, true, (ApplicationContext)null);
}
public FileSystemXmlApplicationContext(String... configLocations) throws BeansException {
this(configLocations, true, (ApplicationContext)null);
}
public FileSystemXmlApplicationContext(String[] configLocations, ApplicationContext parent) throws BeansException {
this(configLocations, true, parent);
}
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh) throws BeansException {
this(configLocations, refresh, (ApplicationContext)null);
}
//这个构造函数很重要它是初始化的入口
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
//它会调用父类AbstractApplicationContext的构造函数来设置ResourceLoader
//即定位资源的资源加载器
super(parent);
//调用父类AbstractRefreshableConfigBeanFactory的setConfigLoactions
//设置加载资源文件的路径
this.setConfigLocations(configLocations);
if (refresh) {
this.refresh();//很关键，Ioc容器的入口函数，它会调用父类AbstractApplicationContext的refresh()
}
}
//FileSystemXmlApplicationContext自己实现的符合自己加载资源文件的方法
//，该方法会在定位资源文件时调用
protected Resource getResourceByPath(String path) {
if (path != null && path.startsWith("/")) {
path = path.substring(1);
}
return new FileSystemResource(path);
}
}
看到这里可能你想看下FileSystemXmlApplicationContext如何加载类加载器和设置加载资源路径以及AbstractRefreshableConfigBeanFactory中的refresh方法是怎么样的，不急，下面一一分析
如何设置类加载器的：
//调用
public AbstractApplicationContext() {
this.logger = LogFactory.getLog(this.getClass());
this.id = ObjectUtils.identityToString(this);
this.displayName = ObjectUtils.identityToString(this);
this.beanFactoryPostProcessors = new ArrayList();
this.active = new AtomicBoolean();
this.closed = new AtomicBoolean();
this.startupShutdownMonitor = new Object();
this.applicationListeners = new LinkedHashSet();
this.resourcePatternResolver = this.getResourcePatternResolver();//这里就是真的开始设置ResourceLoader
}
//这个方法就是获取类加载器的方法
protected ResourcePatternResolver getResourcePatternResolver() {
return new PathMatchingResourcePatternResolver(this);//可以看到这里它把自己即AbstractApplicationContext自 己传递进入参数了，
为什么？因为AbstractApplicationContext本身是DefaultResourceLoader的子类，
本身也是一种类加载器
}
//这个方法才是真的构造类加载器返回类加载器的方法
public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
Assert.notNull(resourceLoader, "ResourceLoader must not be null");
this.resourceLoader = resourceLoader;
}
//这里是FileSystemXmlBeanFactory调用的父类的构造函数
public AbstractApplicationContext(ApplicationContext parent) {
this();//父类构造函数又调用自己无参构造函数
this.setParent(parent);
}
如何设置资源文件加载路径的？
public void setConfigLocations(String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for(int i = 0; i < locations.length; ++i) {
this.configLocations[i] = this.resolvePath(locations[i]).trim();
}
} else {
this.configLocations = null;
}
}
AbstractApplicationContext中的refresh是什么样？
public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor) {
this.prepareRefresh();
ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();//这个方法才是真的启动Ioc容器初始化的方法
this.prepareBeanFactory(beanFactory);//容器启动方法
try {
this.postProcessBeanFactory(beanFactory);
this.invokeBeanFactoryPostProcessors(beanFactory);
this.registerBeanPostProcessors(beanFactory);
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
this.finishBeanFactoryInitialization(beanFactory);//这个方法会对设置了lazy-init属性的bean预实例化
this.finishRefresh();
} catch (BeansException var9) {
if (this.logger.isWarnEnabled()) {
this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
}
this.destroyBeans();
this.cancelRefresh(var9);
throw var9;
} finally {
this.resetCommonCaches();
}
}
}
在上面的ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory()会调用子类AbstractRefreshableApplicationContext的RefreshBeanFactory方法
protected final void refreshBeanFactory() throws BeansException {
if (this.hasBeanFactory()) {//首先判断容器是否存在，存在就销毁并关闭
this.destroyBeans();
this.closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = this.createBeanFactory();//创建一个新容器DefaultListableBeanFactory
beanFactory.setSerializationId(this.getId());
this.customizeBeanFactory(beanFactory);
//这个方法是抽象的会委派给子类AbstractXmlApplicationContext的loadBeanDefinition(factory)
this.loadBeanDefinitions(beanFactory);
Object var2 = this.beanFactoryMonitor;
synchronized(this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
} catch (IOException var5) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var5);
}
}
那么接着看AbstractXmlApplicationContext的loadBeanDefinition(factory)
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//原来在子类实现方法中创建了资源文件解析器XmlBeanDefinitionReader来解析资源文件
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
this.initBeanDefinitionReader(beanDefinitionReader);
//这里调用的是重载方法
this.loadBeanDefinitions(beanDefinitionReader);
}
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = this.getConfigResources();//获取资源文件
if (configResources != null) {
//在这里调用父类AbstractXmlBeanDefinitionReader的loadBeanDefinition方法来加载资源文件
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = this.getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
那就看下父类的加载方法
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
//这里设置资源加载器ResourceLoader
ResourceLoader resourceLoader = this.getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
} else {
int loadCount;
if (!(resourceLoader instanceof ResourcePatternResolver)) {
//调用资源加载器来定位资源
Resource resource = resourceLoader.getResource(location);
//这里调用子类XmlBeanDefinitionReader的loadBeanDefinition方法
loadCount = this.loadBeanDefinitions((Resource)resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
} else {
try {
Resource[] resources = ((ResourcePatternResolver)resourceLoader).getResources(location);
loadCount = this.loadBeanDefinitions(resources);
if (actualResources != null) {
Resource[] var6 = resources;
int var7 = resources.length;
for(int var8 = 0; var8 < var7; ++var8) {
Resource resource = var6[var8];
actualResources.add(resource);
}
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
} catch (IOException var10) {
throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", var10);
}
}
}
}
XmlBeanDefinittionReader的loadBeanDefiniton方法源码如下：
//父类调用的它
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return this.loadBeanDefinitions(new EncodedResource(resource));//调用同类的重载方法
}
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (this.logger.isInfoEnabled()) {
this.logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
Set<EncodedResource> currentResources = (Set)this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!((Set)currentResources).add(encodedResource)) {
throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
} else {
int var5;
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
var5 = this.doLoadBeanDefinitions(inputSource, encodedResource.getResource());//这里它有调用了本类的doLoadBeanDefinition方法来加载资源文件
} finally {
inputStream.close();
}
} catch (IOException var15) {
throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), var15);
} finally {
((Set)currentResources).remove(encodedResource);
if (((Set)currentResources).isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
return var5;
}
}
那么接着看下doLoadBeanDefinition的源码
try {
//安装JAXP的XML解析器来把XML文件解析为document对象
Document doc = this.doLoadDocument(inputSource, resource);
//这里开始按照spring bean规则解析doucment
return this.registerBeanDefinitions(doc, resource);
} catch (BeanDefinitionStoreException var4) {
throw var4;
} catch (SAXParseException var5) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var5.getLineNumber() + " in XML document from " + resource + " is invalid", var5);
} catch (SAXException var6) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var6);
} catch (ParserConfigurationException var7) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var7);
} catch (IOException var8) {
throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var8);
} catch (Throwable var9) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var9);
}
}
接着看下是如何按照spring bean的规则来解析document的
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//原理内部创建了一个BeanDefinitionDocumentReader的对象来解析
BeanDefinitionDocumentReader documentReader = this.createBeanDefinitionDocumentReader();
int countBefore = this.getRegistry().getBeanDefinitionCount();
//这里是它解析的方法，它会委托给它子类DefaultBeanDefinitionDocumentReader的实现方法
documentReader.registerBeanDefinitions(doc, this.createReaderContext(resource));
return this.getRegistry().getBeanDefinitionCount() - countBefore;
}
接着看如何解析的：
protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
//在这里它创建真的用于解析的对象BeanDefinitionParserDelegate
this.delegate = this.createDelegate(this.getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute("profile");
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, ",; ");
if (!this.getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
return;
}
}
}
this.preProcessXml(root);
this.parseBeanDefinitions(root, this.delegate);//解析document
this.postProcessXml(root);
this.delegate = parent;
}
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for(int i = 0; i < nl.getLength(); ++i) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element)node;
if (delegate.isDefaultNamespace(ele)) {
this.parseDefaultElement(ele, delegate);
} else {
delegate.parseCustomElement(ele);
}
}
}
} else {
delegate.parseCustomElement(root);
}
}
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, "import")) {
this.importBeanDefinitionResource(ele);
} else if (delegate.nodeNameEquals(ele, "alias")) {
this.processAliasRegistration(ele);
} else if (delegate.nodeNameEquals(ele, "bean")) {
this.processBeanDefinition(ele, delegate);
} else if (delegate.nodeNameEquals(ele, "beans")) {
this.doRegisterBeanDefinitions(ele);
}
}
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//调用delegate解析document生成BeanDefinitionHolder，该对象是BeanDefinition的包装类
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//这里是注册BeanDefinitaion的方法，其委托给了DefaultListableBeanFactory的实现方法
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
} catch (BeanDefinitionStoreException var5) {
this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
}
this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
那么就看下具体怎么注册的
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition)beanDefinition).validate();
} catch (BeanDefinitionValidationException var9) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
}
}
BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!this.isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound.");
}
if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
} else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
} else if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
this.beanDefinitionMap.put(beanName, beanDefinition);
} else {
if (this.hasBeanCreationStarted()) {
Map var4 = this.beanDefinitionMap;
synchronized(this.beanDefinitionMap) {//加锁
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
} else {
//这里就是注册的实现，即把baseName对应的BeanDefinition注册进ConcurrentHashMap中
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || this.containsSingleton(beanName)) {
this.resetBeanDefinition(beanName);
}
}
到此，Ioc的初始化就完成了，当还差依赖注入。。。。。
说明下，依赖注入其实包含两步，一是根据BeanDefinition记录的信息来创建实例，二是为创建的对象的属性赋值。而这些步骤都发生在getBean()方法的调用，即第一次向容器索要对象实例时发生。下面就来看下具体的源码过程。
对于FileSystemXmlApplicationContext的getBean()会调用AbstractBeanFactory的getBean方法
//发现，AbstractBeanFactory的getBean方法全都调用了doGetBean()方法
public Object getBean(String name) throws BeansException {
return this.doGetBean(name, (Class)null, (Object[])null, false);
}
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
return this.doGetBean(name, requiredType, (Object[])null, false);
}
public Object getBean(String name, Object... args) throws BeansException {
return this.doGetBean(name, (Class)null, args, false);
}
public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {
return this.doGetBean(name, requiredType, args, false);
}
//doGetBean方法源码
protected <T> T doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
final String beanName = this.transformedBeanName(name);
Object sharedInstance = this.getSingleton(beanName);
Object bean;
if (sharedInstance != null && args == null) {
if (this.logger.isDebugEnabled()) {
if (this.isSingletonCurrentlyInCreation(beanName)) {
this.logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
} else {
this.logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//这一句和FactoryBean有关，后面再说
bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
} else {
if (this.isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
BeanFactory parentBeanFactory = this.getParentBeanFactory();
if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
String nameToLookup = this.originalBeanName(name);
if (args != null) {
return parentBeanFactory.getBean(nameToLookup, args);
}
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
if (!typeCheckOnly) {
this.markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
this.checkMergedBeanDefinition(mbd, beanName, args);
String[] dependsOn = mbd.getDependsOn();
String[] var11;
if (dependsOn != null) {
var11 = dependsOn;
int var12 = dependsOn.length;
for(int var13 = 0; var13 < var12; ++var13) {
String dependsOnBean = var11[var13];
if (this.isDependent(beanName, dependsOnBean)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
}
this.registerDependentBean(dependsOnBean, beanName);
this.getBean(dependsOnBean);
}
}
if (mbd.isSingleton()) {
sharedInstance = this.getSingleton(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
try {
return AbstractBeanFactory.this.createBean(beanName, mbd, args);
} catch (BeansException var2) {
AbstractBeanFactory.this.destroySingleton(beanName);
throw var2;
}
}
});
//和FactoryBean有关，后面再说
bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
} else if (mbd.isPrototype()) {
var11 = null;
Object prototypeInstance;
try {
this.beforePrototypeCreation(beanName);
//这里说下，这里就是创建bean的方法入口,
会委派给AbstractAutoWireCapableBeanFactory类中的createBean方法
prototypeInstance = this.createBean(beanName, mbd, args);
} finally {
this.afterPrototypeCreation(beanName);
}
bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
} else {
String scopeName = mbd.getScope();
Scope 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>() {
public Object getObject() throws BeansException {
AbstractBeanFactory.this.beforePrototypeCreation(beanName);
Object var1;
try {
var1 = AbstractBeanFactory.this.createBean(beanName, mbd, args);
} finally {
AbstractBeanFactory.this.afterPrototypeCreation(beanName);
}
return var1;
}
});
bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
} catch (IllegalStateException var21) {
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", var21);
}
}
} catch (BeansException var23) {
this.cleanupAfterBeanCreationFailure(beanName);
throw var23;
}
}
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return this.getTypeConverter().convertIfNecessary(bean, requiredType);
} catch (TypeMismatchException var22) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Failed to convert bean '" + name + "' to required type [" + ClassUtils.getQualifiedName(requiredType) + "]", var22);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
} else {
return bean;
}
}
其中AbstractBeanFactory中的createBean方法会委派给AbstrAutoWireCapableBeanFactory，那么就看下该类中的createBean方法源码
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
Class<?> resolvedClass = this.resolveBeanClass(mbd, beanName, new Class[0]);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
try {
mbdToUse.prepareMethodOverrides();
} catch (BeanDefinitionValidationException var7) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", var7);
}
Object beanInstance;
try {
beanInstance = this.resolveBeforeInstantiation(beanName, mbdToUse);
if (beanInstance != null) {
return beanInstance;
}
} catch (Throwable var8) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", var8);
}
//这里它调用了doCreateBean方法
beanInstance = this.doCreateBean(beanName, mbdToUse, args);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
接下来的doCreateBean中方法就比较重要了
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, Object[] args) {
BeanWrapper instanceWrapper = null;//BeanWrapper对Bean的包装类
if (mbd.isSingleton()) {
instanceWrapper = (BeanWrapper)this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//这里又调用了createBeanInstance方法来创实例，可以看到在spring源码中真的是一个委派一个呀。。。
instanceWrapper = this.createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null;
Class<?> beanType = instanceWrapper != null ? instanceWrapper.getWrappedClass() : null;
Object var7 = mbd.postProcessingLock;
synchronized(mbd.postProcessingLock) {
if (!mbd.postProcessed) {
this.applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
mbd.postProcessed = true;
}
}
boolean earlySingletonExposure = mbd.isSingleton() && this.allowCircularReferences && this.isSingletonCurrentlyInCreation(beanName);
if (earlySingletonExposure) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references");
}
this.addSingletonFactory(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
return AbstractAutowireCapableBeanFactory.this.getEarlyBeanReference(beanName, mbd, bean);
}
});
}
Object exposedObject = bean;//真的被返回的对象
try {
this.populateBean(beanName, mbd, instanceWrapper);//这个方法很关键，是处理创建好的实例的依赖的
if (exposedObject != null) {
//实例创建好后，会初始化bean其中会调用init-method方法和如果有后置处理器也会调用后置处理器的回调方法
exposedObject = this.initializeBean(beanName, exposedObject, mbd);
}
} catch (Throwable var17) {
if (var17 instanceof BeanCreationException && beanName.equals(((BeanCreationException)var17).getBeanName())) {
throw (BeanCreationException)var17;
}
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", var17);
}
if (earlySingletonExposure) {
Object earlySingletonReference = this.getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
} else if (!this.allowRawInjectionDespiteWrapping && this.hasDependentBean(beanName)) {
String[] dependentBeans = this.getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet(dependentBeans.length);
String[] var12 = dependentBeans;
int var13 = dependentBeans.length;
for(int var14 = 0; var14 < var13; ++var14) {
String dependentBean = var12[var14];
if (!this.removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName, "Bean with name '" + beanName + "' has been injected into other beans [" + StringUtils.collectionToCommaDelimitedString(actualDependentBeans) + "] in its raw version as part of a circular reference, but has eventually been " + "wrapped. This means that said other beans do not use the final version of the " + "bean. This is often the result of over-eager type matching - consider using " + "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
try {
this.registerDisposableBeanIfNecessary(beanName, bean, mbd);
return exposedObject;
} catch (BeanDefinitionValidationException var16) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", var16);
}
}
那接着看createBeanInstance方法源码把，看如何创建的实例？它会将创建实例的任务全部委派给SimpleInstantionStrategy这个类的instantiate方法
public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner) {
if (bd.getMethodOverrides().isEmpty()) {
Object var5 = bd.constructorArgumentLock;
Constructor constructorToUse;
synchronized(bd.constructorArgumentLock) {
constructorToUse = (Constructor)bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = (Constructor)AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor<?>>() {
public Constructor<?> run() throws Exception {
return clazz.getDeclaredConstructor((Class[])null);
}
});
} else {
constructorToUse = clazz.getDeclaredConstructor((Class[])null);
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
} catch (Exception var9) {
throw new BeanInstantiationException(clazz, "No default constructor found", var9);
}
}
}
//会调用反射来创建对象
return BeanUtils.instantiateClass(constructorToUse, new Object[0]);
} else {
//CGLIB来创建对象
return this.instantiateWithMethodInjection(bd, beanName, owner);
}
}
到此我们就知道是如何创建对象的了，那么实例有了，它的属性和它依赖的对象如何获取呢？这就涉及到依赖注入的第二个步骤，也就是我们上面提示过的populateBean这个方法
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
PropertyValues pvs = mbd.getPropertyValues();
if (bw == null) {
if (!((PropertyValues)pvs).isEmpty()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
} else {
boolean continueWithPropertyPopulation = true;
if (!mbd.isSynthetic() && this.hasInstantiationAwareBeanPostProcessors()) {
Iterator var6 = this.getBeanPostProcessors().iterator();
while(var6.hasNext()) {
BeanPostProcessor bp = (BeanPostProcessor)var6.next();
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor)bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
continueWithPropertyPopulation = false;
break;
}
}
}
}
if (continueWithPropertyPopulation) {
if (mbd.getResolvedAutowireMode() == 1 || mbd.getResolvedAutowireMode() == 2) {
MutablePropertyValues newPvs = new MutablePropertyValues((PropertyValues)pvs);
if (mbd.getResolvedAutowireMode() == 1) {
this.autowireByName(beanName, mbd, bw, newPvs);
}
if (mbd.getResolvedAutowireMode() == 2) {
this.autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = this.hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = mbd.getDependencyCheck() != 0;
if (hasInstAwareBpps || needsDepCheck) {
PropertyDescriptor[] filteredPds = this.filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
Iterator var9 = this.getBeanPostProcessors().iterator();
while(var9.hasNext()) {
BeanPostProcessor bp = (BeanPostProcessor)var9.next();
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor)bp;
pvs = ibp.postProcessPropertyValues((PropertyValues)pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
this.checkDependencies(beanName, mbd, filteredPds, (PropertyValues)pvs);
}
}
this.applyPropertyValues(beanName, mbd, bw, (PropertyValues)pvs);
}
}
}
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
if (pvs != null && !pvs.isEmpty()) {
MutablePropertyValues mpvs = null;
if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
((BeanWrapperImpl)bw).setSecurityContext(this.getAccessControlContext());
}
List original;
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues)pvs;
if (mpvs.isConverted()) {
try {
bw.setPropertyValues(mpvs);
return;
} catch (BeansException var18) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Error setting property values", var18);
}
}
original = mpvs.getPropertyValueList();
} else {
original = Arrays.asList(pvs.getPropertyValues());
}
TypeConverter converter = this.getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, (TypeConverter)converter);
List<PropertyValue> deepCopy = new ArrayList(original.size());
boolean resolveNecessary = false;
Iterator var11 = original.iterator();
while(true) {
while(var11.hasNext()) {
PropertyValue pv = (PropertyValue)var11.next();
if (pv.isConverted()) {
deepCopy.add(pv);
} else {
String propertyName = pv.getName();
Object originalValue = pv.getValue();
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) && !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = this.convertForProperty(resolvedValue, propertyName, bw, (TypeConverter)converter);
}
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
} else if (convertible && originalValue instanceof TypedStringValue && !((TypedStringValue)originalValue).isDynamic() && !(convertedValue instanceof Collection) && !ObjectUtils.isArray(convertedValue)) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
} else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}
try {
//这里开始设置属性，会委派给BeanWrapperImp
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
return;
} catch (BeansException var19) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Error setting property values", var19);
}
}
}
}
对属性的注入过程分以下两种情况：
(1)属性值类型不需要转换时，不需要解析属性值，直接准备进行依赖注入。
(2)属性值需要进行类型转换时，如对其他对象的引用等，首先需要解析属性值，然后对解析后的属性值进行依赖注入。
protected void setPropertyValue(AbstractNestablePropertyAccessor.PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
String propertyName = tokens.canonicalName;
String actualName = tokens.actualName;
Object propValue;
if (tokens.keys != null) {
AbstractNestablePropertyAccessor.PropertyTokenHolder getterTokens = new AbstractNestablePropertyAccessor.PropertyTokenHolder();
getterTokens.canonicalName = tokens.canonicalName;
getterTokens.actualName = tokens.actualName;
getterTokens.keys = new String[tokens.keys.length - 1];
System.arraycopy(tokens.keys, 0, getterTokens.keys, 0, tokens.keys.length - 1);
try {
propValue = this.getPropertyValue(getterTokens);
} catch (NotReadablePropertyException var20) {
throw new NotWritablePropertyException(this.getRootClass(), this.nestedPath + propertyName, "Cannot access indexed value in property referenced in indexed property path '" + propertyName + "'", var20);
}
String key = tokens.keys[tokens.keys.length - 1];
if (propValue == null) {
if (!this.isAutoGrowNestedPaths()) {
throw new NullValueInNestedPathException(this.getRootClass(), this.nestedPath + propertyName, "Cannot access indexed value in property referenced in indexed property path '" + propertyName + "': returned null");
}
int lastKeyIndex = tokens.canonicalName.lastIndexOf(91);
getterTokens.canonicalName = tokens.canonicalName.substring(0, lastKeyIndex);
propValue = this.setDefaultValue(getterTokens);
}
Class requiredType;
Object convertedValue;
Object newArray;
AbstractNestablePropertyAccessor.PropertyHandler ph;
if (propValue.getClass().isArray()) {
ph = this.getLocalPropertyHandler(actualName);
requiredType = propValue.getClass().getComponentType();
int arrayIndex = Integer.parseInt(key);
Object oldValue = null;
try {
if (this.isExtractOldValueForEditor() && arrayIndex < Array.getLength(propValue)) {
oldValue = Array.get(propValue, arrayIndex);
}
convertedValue = this.convertIfNecessary(propertyName, oldValue, pv.getValue(), requiredType, ph.nested(tokens.keys.length));
int length = Array.getLength(propValue);
if (arrayIndex >= length && arrayIndex < this.autoGrowCollectionLimit) {
Class<?> componentType = propValue.getClass().getComponentType();
newArray = Array.newInstance(componentType, arrayIndex + 1);
System.arraycopy(propValue, 0, newArray, 0, length);
this.setPropertyValue(actualName, newArray);
propValue = this.getPropertyValue(actualName);
}
Array.set(propValue, arrayIndex, convertedValue);
} catch (IndexOutOfBoundsException var19) {
throw new InvalidPropertyException(this.getRootClass(), this.nestedPath + propertyName, "Invalid array index in property path '" + propertyName + "'", var19);
}
} else {
Object convertedValue;
if (propValue instanceof List) {
ph = this.getPropertyHandler(actualName);
requiredType = ph.getCollectionType(tokens.keys.length);
List<Object> list = (List)propValue;
int index = Integer.parseInt(key);
convertedValue = null;
if (this.isExtractOldValueForEditor() && index < list.size()) {
convertedValue = list.get(index);
}
convertedValue = this.convertIfNecessary(propertyName, convertedValue, pv.getValue(), requiredType, ph.nested(tokens.keys.length));
int size = list.size();
if (index >= size && index < this.autoGrowCollectionLimit) {
for(int i = size; i < index; ++i) {
try {
list.add((Object)null);
} catch (NullPointerException var18) {
throw new InvalidPropertyException(this.getRootClass(), this.nestedPath + propertyName, "Cannot set element with index " + index + " in List of size " + size + ", accessed using property path '" + propertyName + "': List does not support filling up gaps with null elements");
}
}
list.add(convertedValue);
} else {
try {
list.set(index, convertedValue);
} catch (IndexOutOfBoundsException var17) {
throw new InvalidPropertyException(this.getRootClass(), this.nestedPath + propertyName, "Invalid list index in property path '" + propertyName + "'", var17);
}
}
} else {
if (!(propValue instanceof Map)) {
throw new InvalidPropertyException(this.getRootClass(), this.nestedPath + propertyName, "Property referenced in indexed property path '" + propertyName + "' is neither an array nor a List nor a Map; returned value was [" + propValue + "]");
}
ph = this.getLocalPropertyHandler(actualName);
requiredType = ph.getMapKeyType(tokens.keys.length);
Class<?> mapValueType = ph.getMapValueType(tokens.keys.length);
Map<Object, Object> map = (Map)propValue;
TypeDescriptor typeDescriptor = TypeDescriptor.valueOf(requiredType);
convertedValue = this.convertIfNecessary((String)null, (Object)null, key, requiredType, typeDescriptor);
Object oldValue = null;
if (this.isExtractOldValueForEditor()) {
oldValue = map.get(convertedValue);
}
newArray = this.convertIfNecessary(propertyName, oldValue, pv.getValue(), mapValueType, ph.nested(tokens.keys.length));
map.put(convertedValue, newArray);
}
}
} else {
AbstractNestablePropertyAccessor.PropertyHandler ph = this.getLocalPropertyHandler(actualName);
if (ph == null || !ph.isWritable()) {
if (pv.isOptional()) {
if (logger.isDebugEnabled()) {
logger.debug("Ignoring optional value for property '" + actualName + "' - property not found on bean class [" + this.getRootClass().getName() + "]");
}
return;
} else {
throw this.createNotWritablePropertyException(propertyName);
}
}
propValue = null;
PropertyChangeEvent propertyChangeEvent;
try {
Object originalValue = pv.getValue();
Object valueToApply = originalValue;
if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
if (pv.isConverted()) {
valueToApply = pv.getConvertedValue();
} else {
if (this.isExtractOldValueForEditor() && ph.isReadable()) {
try {
propValue = ph.getValue();
} catch (Exception var21) {
Exception ex = var21;
if (var21 instanceof PrivilegedActionException) {
ex = ((PrivilegedActionException)var21).getException();
}
if (logger.isDebugEnabled()) {
logger.debug("Could not read previous value of property '" + this.nestedPath + propertyName + "'", ex);
}
}
}
valueToApply = this.convertForProperty(propertyName, propValue, originalValue, ph.toTypeDescriptor());
}
pv.getOriginalPropertyValue().conversionNecessary = valueToApply != originalValue;
}
ph.setValue(this.object, valueToApply);
} catch (TypeMismatchException var22) {
throw var22;
} catch (InvocationTargetException var23) {
propertyChangeEvent = new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, propValue, pv.getValue());
if (var23.getTargetException() instanceof ClassCastException) {
throw new TypeMismatchException(propertyChangeEvent, ph.getPropertyType(), var23.getTargetException());
}
Throwable cause = var23.getTargetException();
if (cause instanceof UndeclaredThrowableException) {
cause = cause.getCause();
}
throw new MethodInvocationException(propertyChangeEvent, cause);
} catch (Exception var24) {
propertyChangeEvent = new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, propValue, pv.getValue());
throw new MethodInvocationException(propertyChangeEvent, var24);
}
}
}
(1)对于集合类型的属性，将其属性值解析为目标类型的集合后直接赋值给属性。
(2)对于非集合类型的属性，大量使用了JDK的反射和内省机制，通过属性的getter方法(reader method)获取指定属性注入以前的值，同时调用属性的setter方法(writer method)为属性设置注入后的值。
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