背景
使用了很久 Spring，但对 Spring 的内在实现并不了解，正好最近有些时间，研究下 Spring 的源码
首先写一个测试方法
BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beans.xml"));
User userTest = (User) bf.getBean("testBean");
System.out.println(userTest.getEmail());和对应的配置文件 beans.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:myName="http://www.wjs.com/schema/user"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
http://www.wjs.com/schema/user http://www.wjs.com/schema/user.xsd">
<bean id = "testBean" class="com.zero.pojo.User">
<property name="userName" value="zhang"></property>
<property name="email" value = "18"></property>
</bean>
</beans>
以上代码的功能使用过 Spring 的都能猜出来
- 读取配置文件 beans.xml
- 根据 beans.xml 中的配置找到对应的类，并进行实例化
- 调用实例化后的类
现在开始调试代码
1.1 初始化 ClassPathResource
new ClassPathResource(“beans.xml”)
进入代码时首先执行了new ClassPathResource(“beans.xml”)，在这里加载了配置文件路径到 ClassPathResource 的 path 属性中。
public ClassPathResource(String path) {this(path, (ClassLoader)null);
}
public ClassPathResource(String path, @Nullable ClassLoader classLoader) {Assert.notNull(path, "Path must not be null");
String pathToUse = StringUtils.cleanPath(path);
if (pathToUse.startsWith("/")) {pathToUse = pathToUse.substring(1);
}
this.path = pathToUse;
this.classLoader = classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader();}1.2 初始化 XmlBeanFactory
new XmlBeanFactory(new ClassPathResource(“beans.xml”))
初始化 ClassPathResource 后，开始初始化 XmlBeanFactory，在构造函数内部再调用构造函数，this.reader.loadBeanDefinitions(resource);这个才是资源加载的真正实现
public XmlBeanFactory(Resource resource) throws BeansException {// 调用 XmlBeanFactory(Resource, BeanFactory)构造方法
this(resource, (BeanFactory)null);
}
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {super(parentBeanFactory);
this.reader = new XmlBeanDefinitionReader(this);
this.reader.loadBeanDefinitions(resource);
}1.2.1 调用 AbstractAutowireCapableBeanFactory 的构造方法
super(parentBeanFactory);
不过在此之前还有一个 super(parentBeanFactory); 它会一直调用到 AbstractAutowireCapableBeanFactory 的构造方法中，这里的 ignoreDependencyInterface 的主要功能是忽略给定接口的自动装配功能，当有忽略的接口类，自动装配会忽略这部分类的初始化装配，因为某种情况下，此时的接口实现类不能初始化
public AbstractAutowireCapableBeanFactory() {this.instantiationStrategy = new CglibSubclassingInstantiationStrategy();
this.parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
this.allowCircularReferences = true;
this.allowRawInjectionDespiteWrapping = false;
this.ignoredDependencyTypes = new HashSet();
this.ignoredDependencyInterfaces = new HashSet();
this.currentlyCreatedBean = new NamedThreadLocal("Currently created bean");
this.factoryBeanInstanceCache = new ConcurrentHashMap();
this.factoryMethodCandidateCache = new ConcurrentHashMap();
this.filteredPropertyDescriptorsCache = new ConcurrentHashMap();
this.ignoreDependencyInterface(BeanNameAware.class);
this.ignoreDependencyInterface(BeanFactoryAware.class);
this.ignoreDependencyInterface(BeanClassLoaderAware.class);
}1.2.2 设置变量 reader
this.reader = new XmlBeanDefinitionReader(this);
执行完父类的构造方法后，开始设置变量this.reader = new XmlBeanDefinitionReader(this);
public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
// 执行 AbstractBeanDefinitionReader 构造方法
super(registry);
this.errorHandler = new SimpleSaxErrorHandler(this.logger);
this.validationModeDetector = new XmlValidationModeDetector();
this.resourcesCurrentlyBeingLoaded = new NamedThreadLocal("XML bean definition resources currently being loaded");
}
// 设置 resourceLoader 和 environment
protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
this.registry = registry;
// 设置 resourceLoader
if (this.registry instanceof ResourceLoader) {this.resourceLoader = (ResourceLoader)this.registry;
} else {this.resourceLoader = new PathMatchingResourcePatternResolver();
}
// 设置 environment
if (this.registry instanceof EnvironmentCapable) {this.environment = ((EnvironmentCapable)this.registry).getEnvironment();} else {this.environment = new StandardEnvironment();
}
}
1.2.3 资源加载
this.reader.loadBeanDefinitions(resource);
设置完变量后开始执行 this.reader.loadBeanDefinitions(resource) 进行资源加载
方法 pkg：org.springframework.beans.factory.xml
- 封装资源文件，当进入 XmlBeanDefinitionReader 后首先对参数 Resource 使用 EncodedResource 类进行封装
- 获取输入流，从 Resource 中获取对应 InputStream 并构造 InputSource
- 通过构造的 InputSource 实例和 Resource 实例继续调用函数 doLoadBeanDefinitions
loadBeanDefinitions 具体实现过程
构造好 encodedResource 对象后，再次转入 loadBeanDefinitions，这个方法内部才是真正的数据准备阶段
对传入的 resource 参数做封装，目的是考虑到 Resource 可能存在编码要求的情况，其次，通过 SAX 读取 XML 文件的方式来准备 InputSource 对象，最后将准备的数据通过参数传入真正的核心处理部分this.doLoadBeanDefinitions(inputSource, encodedResource.getResource())
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {return this.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());
}
// 通过属性记录已加载的资源
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException("Detected cyclic loading of" + encodedResource + "- check your import definitions!");
}
try {
// 从 encodedResource 中获取已经封装的 Resource 对象并再次从 Resource 中获取其中的 inputStream
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//InputSource 这个类不来自 Spring，全路径是 org.xml.sax.InputSource
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {inputSource.setEncoding(encodedResource.getEncoding());
}
// 核心方法
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
// 关闭输入流
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();
}
}
}1.3 加载 XML 文件根据得到的 Document 信息注册 Bean
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
doLoadBeanDefinitions
- 加载 XML 文件，并得到对应的 Document Document doc = doLoadDocument(inputSource, resource);
- 根据返回的 Document 注册 Bean 信息 return registerBeanDefinitions(doc, resource)
这些步骤支撑整个 Spring 容器部分的实现
/**
* 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);
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
- 获取 XML 文件的验证模式 DTD(文档类型定义)还是 XSD (XML Schema 语言) this.getValidationModeForResource(resource)
-
加载 XML 文件，得到对应 Document
protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {return this.documentLoader.loadDocument(inputSource, this.getEntityResolver(), this.errorHandler, this.getValidationModeForResource(resource), this.isNamespaceAware()); }
1.3.1 获取资源的验证模式
this.getValidationModeForResource(resource)
/**
* Gets the validation mode for the specified {@link Resource}. If no explicit
* validation mode has been configured then the validation mode is
* {@link #detectValidationMode detected}.
* <p>Override this method if you would like full control over the validation
* mode, even when something other than {@link #VALIDATION_AUTO} was set.
*/
protected int getValidationModeForResource(Resource resource) {int validationModeToUse = getValidationMode();
// 如果手动指定了使用手动指定的验证模式类型的
if (validationModeToUse != VALIDATION_AUTO) {return validationModeToUse;}
// 未指定使用自动检测
int detectedMode = detectValidationMode(resource);
if (detectedMode != VALIDATION_AUTO) {return detectedMode;}
// Hmm, we didn't get a clear indication... Let's assume XSD,
// since apparently no DTD declaration has been found up until
// detection stopped (before finding the document's root tag).
return VALIDATION_XSD;
}1.3.2 自动判断资源认证模式
自动判断实际就是获取资源的输入流，判断是否包含 DOCTPE
DTD 模式 XML 文件带有 <!DOCTYPE beans PU…. 而 XSD 不带
int detectedMode = detectValidationMode(resource);
/**
* Detect the validation mode for the XML document in the supplied {@link InputStream}.
* Note that the supplied {@link InputStream} is closed by this method before returning.
* @param inputStream the InputStream to parse
* @throws IOException in case of I/O failure
* @see #VALIDATION_DTD
* @see #VALIDATION_XSD
*/
public int detectValidationMode(InputStream inputStream) throws IOException {
// Peek into the file to look for DOCTYPE.
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
try {
boolean isDtdValidated = false;
String content;
while ((content = reader.readLine()) != null) {content = consumeCommentTokens(content);
if (this.inComment || !StringUtils.hasText(content)) {continue;}
if (hasDoctype(content)) {
isDtdValidated = true;
break;
}
if (hasOpeningTag(content)) {
// End of meaningful data...
break;
}
}
return (isDtdValidated ? VALIDATION_DTD : VALIDATION_XSD);
}
catch (CharConversionException ex) {
// Choked on some character encoding...
// Leave the decision up to the caller.
return VALIDATION_AUTO;
}
finally {reader.close();
}
}hasDoctype(content)
/**
* Does the content contain the DTD DOCTYPE declaration?
*/
private boolean hasDoctype(String content) {return content.contains(DOCTYPE);
}1.4 加载 Document
- 加载 Document
this.documentLoader.loadDocument(inputSource, this.getEntityResolver(), this.errorHandler, this.getValidationModeForResource(resource), this.isNamespaceAware());
/**
* Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
* XML parser.
*/
@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);
return builder.parse(inputSource);
}创建 DocumentBuilderFactory，再通过 DocumentBuilderFactory 创建 DocumentBuilder，进而解析 inputSource 来返回 Document
1.5 注册 Bean 信息
- 根据返回的 Document 注册 Bean 信息
在将文件转换为 Document 后，接下来就是提取和注册 bean，当程序已经有了 XML 文件的 Document 实例和上下文信息后
int count = this.registerBeanDefinitions(doc, resource);
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 使用 DefaultBeanDefinitionDocumentReader 实例化 BeanDefinitionDocumentReader
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 记录统计前 BeanDefinition 的加载个数
int countBefore = getRegistry().getBeanDefinitionCount();
// 加载及注册 bean
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 记录本次加载的 BeanDefinition 个数
return getRegistry().getBeanDefinitionCount() - countBefore;
}1.5.1 实例化 createBeanDefinitionDocumentReader
createBeanDefinitionDocumentReader
BeanDefinitionDocumentReader 是一个接口，实例化工作是在 createBeanDefinitionDocumentReader 中执行，通过此方法，BeanDefinitionDocumentReader 已经转变成了 DefaultBeanDefinitionDocumentReader
createBeanDefinitionDocumentReader
private Class<? extends BeanDefinitionDocumentReader> documentReaderClass = DefaultBeanDefinitionDocumentReader.class;
/**
* Create the {@link BeanDefinitionDocumentReader} to use for actually
* reading bean definitions from an XML document.
* <p>The default implementation instantiates the specified "documentReaderClass".
* @see #setDocumentReaderClass
*/
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
} public static <T> T instantiateClass(Class<T> clazz) throws BeanInstantiationException {Assert.notNull(clazz, "Class must not be null");
if (clazz.isInterface()) {throw new BeanInstantiationException(clazz, "Specified class is an interface");
} else {
try {return instantiateClass(clazz.getDeclaredConstructor());
} catch (NoSuchMethodException var3) {Constructor<T> ctor = findPrimaryConstructor(clazz);
if (ctor != null) {return instantiateClass(ctor);
} else {throw new BeanInstantiationException(clazz, "No default constructor found", var3);
}
} catch (LinkageError var4) {throw new BeanInstantiationException(clazz, "Unresolvable class definition", var4);
}
}
}1.5.2BeanDefinition 的注册
进入 DefaultBeanDefinitionDocumentReader 后，开始提取 root，并将提取到的 root 作为参数进行 BeanDefinition 的注册
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
/**
* 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;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
doRegisterBeanDefinitions(root);
这里就是逻辑的核心
doRegisterBeanDefinitions(root);
/**
* Register each bean definition within the given root {@code <beans/>} element.
* 在给定的根 {@code <beans />} 元素中注册每个 bean 定义
*/
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)) {
// 处理 profile 属性，使用 profile 来读取不同的配置文件，切换使用不同的环境（DEV/PRD）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;
}
}
}
// 解析前处理，留给子类实现, 模板方法模式，如果继承自 DefaultBeanDefinitionDocumentReader 的子类需要在 Bean 解析前后做操作，只需要重写这两个类就行了
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
// 解析后处理，留给子类实现
postProcessXml(root);
this.delegate = parent;
}1.5.3 解析 profile 属性
处理 profile 属性，使用 profile 来读取不同的配置文件，切换使用不同的环境（DEV/PRD）
root.getAttribute(PROFILE_ATTRIBUTE);
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);1.5.4 解析并注册 BeanDefinition
parseBeanDefinitions(root, this.delegate);
处理掉 profile 后，就可以开始进行 XML 的读取了，Spring 的 XML 配置文件中有两大类 Bean 声明，默认命名空间和自定义命名空间，接下来就是判断命名空间类型并进行相应解析
- 默认命名空间
<bean id = "testBean" class="com.zero.pojo.User">
<property name="userName" value="zhang"></property>
<property name="email" value = "18"></property>
</bean>- 自定义命名空间
<myName:user id="testBean" userName="name" email="A"/>parseBeanDefinitions(root, this.delegate);
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
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;
// 对 bean 的处理
// 默认命名空间
if (delegate.isDefaultNamespace(ele)) {parseDefaultElement(ele, delegate);
}
// 自定义命名空间
else {delegate.parseCustomElement(ele);
}
}
}
}
else {delegate.parseCustomElement(root);
}
}