Spring IOC源码实现流程

最近一段时间学习了IOC的源码实现，分享一下大概流程

创建一个测试类 代码如下：

package com.zcg.learn.Test;

import org.junit.Test;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;

import com.zcg.learn.UserDaoImpl;
import com.zcg.learn.UserServiceImpl;
/**
* spring源码测试类
* @author zcg
* 2019/2/1
*
*/
public class BeanFactoryTest {

@Test
public void createBeanTest() {
DefaultListableBeanFactory factory= new DefaultListableBeanFactory();
UserServiceImpl bean = factory.createBean(UserServiceImpl.class);
System.out.println(bean);
}

/**
* bean的存储
*/
@Test
public void beanStoreTest() {
DefaultListableBeanFactory factory= new DefaultListableBeanFactory();
//单例模式的bean的存储
factory.registerSingleton("userServiceImpl", new UserServiceImpl());
UserServiceImpl userServiceImpl = (UserServiceImpl) factory.getBean("userServiceImpl");
System.out.println(userServiceImpl+"====");

userServiceImpl.addUser();
}

/**
* 依赖关系的注入
*/
@Test
public void dependcsTest() {
DefaultListableBeanFactory factory= new DefaultListableBeanFactory();
factory.registerSingleton("userDao", new UserDaoImpl());
UserServiceImpl userServiceImpl = (UserServiceImpl) factory.createBean(UserServiceImpl.class,
AbstractBeanDefinition.AUTOWIRE_BY_TYPE, true);

System.out.println(userServiceImpl+"====");

userServiceImpl.addUser();
}

@Test
public void getBeanTest() {
DefaultListableBeanFactory factory= new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
reader.loadBeanDefinitions("spring.xml");
UserServiceImpl bean = factory.getBean(UserServiceImpl.class);
//UserServiceImpl bean1 = (UserServiceImpl) factory.getBean("111");
System.out.println("得到的bean"+bean);
}
}

对
@Test
public void getBeanTest() {
DefaultListableBeanFactory factory= new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
reader.loadBeanDefinitions("spring.xml");
UserServiceImpl bean = factory.getBean(UserServiceImpl.class);
//UserServiceImpl bean1 = (UserServiceImpl) factory.getBean("111");
System.out.println("得到的bean"+bean);
}这个方法分析下

首先看下BeanDefinition的加载，解析和注册过程

1.在AbstractBeanDefinitionReader类中将文件位置转换成resource 具体代码如下

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}

if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {

//将位置对应的文件转换成 resources,并执行loadBeanDefinitions（resources）
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int loadCount = loadBeanDefinitions(resources);
if (actualResources != null) {
for (Resource resource : resources) {
actualResources.add(resource);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
// Can only load single resources by absolute URL.
Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}

2.在XmlBeanDefinitionReader类中加载文件 loadBeanDefinitions（resources）具体代码如下

@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}

Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {

//得到输入流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {

//对输入流设置编码
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}

其中 doLoadBeanDefinitions(inputSource, encodedResource.getResource())具体访问如下：

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {

//将输入流转换成Document
Document doc = doLoadDocument(inputSource, resource);

//对doc进行注入
return registerBeanDefinitions(doc, resource);

}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}

doLoadDocument(inputSource, resource)主要代码如下：

protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
getValidationModeForResource(resource), isNamespaceAware());
}

3.loadDocument方法主要是调用DefaultDocumentLoader类中的方法

public class DefaultDocumentLoader implements DocumentLoader {

/**
* Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
* XML parser.
* inputSource 接收的文件流
* 加载转换成document
*/
@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {

DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
//转换成文档
return builder.parse(inputSource);
}

}

4.registerBeanDefinitions(doc, resource)方法主要代码  如下

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}

documentReader.registerBeanDefinitions(doc, createReaderContext(resource))主要是DefaultBeanDefinitionDocumentReader类下的方法

public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader {

@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}

//对解析的doc的root元素进行注册

protected void doRegisterBeanDefinitions(Element root) {

// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);

if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}

preProcessXml(root);

// 对root解析成BeanDefinitions
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);

this.delegate = parent;
}

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {

// 得到root下的所有的节点
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)) {
//解析Element 
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {

//解析import标签
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}

//解析alias标签
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
//解析bean
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
//解析beans标签，就是进行递归解析
doRegisterBeanDefinitions(ele);
}
}

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {

//将Element 转换成 BeanDefinitionHolder 
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}

}

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry())是BeanDefinitionReaderUtils类下的方法  核心代码如下

public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {

// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}

5.registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());主要是DefaultListableBeanFactory 类对解析好点的BeanDefinition进行注入到facotry中

@SuppressWarnings("serial")
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {

@Override
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 ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}

BeanDefinition oldBeanDefinition;

oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
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 (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}

if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}

}