IOC代码
ClassPathResource resource = new ClassPathResource("bean.xml");
DefaultListableBeanFactory factory = newvDefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
reader.loadBeanDefinitions(resource);
资源定位
Resource
- FileSystemResource ：对 java.io.File 类型资源的封装，只要是跟 File 打交道的，基本上与 FileSystemResource 也可以打交道。支持文件和 URL 的形式，实现 WritableResource 接口，且从 Spring Framework 5.0 开始，FileSystemResource 使用 NIO2 API进行读/写交互。
- ByteArrayResource ：对字节数组提供的数据的封装。如果通过 InputStream 形式访问该类型的资源，该实现会根据字节数组的数据构造一个相应的 ByteArrayInputStream。
- UrlResource ：对 java.net.URL类型资源的封装。内部委派 URL 进行具体的资源操作。
- ClassPathResource ：class path 类型资源的实现。使用给定的 ClassLoader 或者给定的 Class 来加载资源。
- InputStreamResource ：将给定的 InputStream 作为一种资源的 Resource 的实现类。
装载
AbstractBeanDefinitionReader 实现 BeanDefinitionReader 的 loadBeanDefinitions 接口
int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException;
private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded = new NamedThreadLocal<>("XML bean definition resources currently being loaded");
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
// <1> 获取已经加载过的资源
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) { // 将当前资源加入记录中。如果已存在，抛出异常
throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
// <2> 从 EncodedResource 获取封装的 Resource ，并从 Resource 中获取其中的 InputStream
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) { // 设置编码
inputSource.setEncoding(encodedResource.getEncoding());
}
// 核心逻辑部分，执行加载 BeanDefinition
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
} finally {
inputStream.close();
}
} catch (IOException ex) {
throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), ex);
} finally {
// 从缓存中剔除该资源 <3>
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
doLoadBeanDefinitions： 解析文件，获取 Document 对象。
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource);
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
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);
}
}
该方法接受五个参数：
- inputSource ：加载 Document 的 Resource 源。
- entityResolver ：解析文件的解析器。
- errorHandler ：处理加载 Document 对象的过程的错误。
- validationMode ：验证模式。
- namespaceAware ：命名空间支持。如果要提供对 XML 名称空间的支持，则为 true 。
注册BeanDefinition
对docment对象进行解析
// AbstractBeanDefinitionReader.java
private final BeanDefinitionRegistry registry;
// XmlBeanDefinitionReader.java
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// <1> 创建 BeanDefinitionDocumentReader 对象
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// <2> 获取已注册的 BeanDefinition 数量
int countBefore = getRegistry().getBeanDefinitionCount();
// <3> 创建 XmlReaderContext 对象
// <4> 注册 BeanDefinition
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 计算新注册的 BeanDefinition 数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
BeanDefinitionDocumentReader 的
void registerBeanDefinitions(Document doc, XmlReaderContext readerContext)throws BeanDefinitionStoreException;
BeanDefinitionParserDelegate：解析 BeanDefinition
protected BeanDefinitionParserDelegate createDelegate(
XmlReaderContext readerContext, Element root, @Nullable BeanDefinitionParserDelegate parentDelegate) {
// 创建 BeanDefinitionParserDelegate 对象
BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
// 初始化默认
delegate.initDefaults(root, parentDelegate);
return delegate;
}
DefaultBeanDefinitionDocumentReader
@Nullable
private XmlReaderContext readerContext;
@Nullable
private BeanDefinitionParserDelegate delegate;
/**
* This implementation parses bean definitions according to the "spring-beans" XSD
* (or DTD, historically).
* <p>Opens a DOM Document; then initializes the default settings
* specified at the {@code <beans/>} level; then parses the contained bean definitions.
*/
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
// 获得 XML Document Root Element
// 执行注册 BeanDefinition
doRegisterBeanDefinitions(doc.getDocumentElement());
}
/**
* Register each bean definition within the given root {@code <beans/>} element.
*/
@SuppressWarnings("deprecation") // for Environment.acceptsProfiles(String...)
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.
// 记录老的 BeanDefinitionParserDelegate 对象
BeanDefinitionParserDelegate parent = this.delegate;
// <1> 创建 BeanDefinitionParserDelegate 对象，并进行设置到 delegate
this.delegate = createDelegate(getReaderContext(), root, parent);
// <2> 检查 <beans /> 根标签的命名空间是否为空，或者是 http://www.springframework.org/schema/beans
if (this.delegate.isDefaultNamespace(root)) {
// <2.1> 处理 profile 属性。可参见《Spring3自定义环境配置 <beans profile="">》http://nassir.iteye.com/blog/1535799
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
// <2.2> 使用分隔符切分，可能有多个 profile 。
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// <2.3> 如果所有 profile 都无效，则不进行注册
// We cannot use Profiles.of(...) since profile expressions are not supported
// in XML config. See SPR-12458 for details.
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
// <3> 解析前处理(子类去做)
preProcessXml(root);
// <4> 解析
parseBeanDefinitions(root, this.delegate);
// <5> 解析后处理(子类去做)
postProcessXml(root);
// 设置 delegate 回老的 BeanDefinitionParserDelegate 对象
this.delegate = parent;
}
解析
解析工作分为三步：
- 1、解析默认标签。
- 2、解析默认标签后下得自定义标签。
- 3、注册解析后的 BeanDefinition 。
DefaultBeanDefinitionDocumentReader
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)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
解析默认标签
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
解析默认标签后下得自定义标签
BeanDefinitionParserDelegate.java
public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
if (namespaceUri == null) {
return null;
}
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
注册解析后的BeanDefinition
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
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.java
/**
* Register the given bean definition with the given bean factory.
* @param definitionHolder the bean definition including name and aliases
* @param registry the bean factory to register with
* @throws BeanDefinitionStoreException if registration failed
*/
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);
}
}
}
IOC 存放注册BeanDefinition的map
DefaultListableBeanFactory.java 对 BeanDefinitionRegistry接口的实现
/** Map of bean definition objects, keyed by bean name. */private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
@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 existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] 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<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
总结流程图
小结
至此，整个 IoC 的初始化过程就已经完成了，从 Bean 资源的定位，转换为 Document 对象，接着对其进行解析，最后注册到 IoC 容器中，都已经完美地完成了。现在 IoC 容器中已经建立了整个 Bean 的配置信息，这些 Bean 可以被检索、使用、维护，他们是控制反转的基础，是后面注入 Bean 的依赖。
