spring 源码-beans(一)

1 spring-beans概要

spring-beans 是sping两大核心组件之一,另一核心组件为spring-context,
两者也都依赖spring-core包,但spring-context依赖spring-beans实现;
spring-beans 是ioc实现的核心,spring其它相关组件的实现都有依赖于它;
《spring 源码-beans(一)》

2 测试demo分析

从常用到的XmlBeanfactory开始分析

public class Test1 {
  public static void main(String[] args){
    ClassPathResource classPathResource = new ClassPathResource("spring-beans.xml");
    BeanFactory factory = new XmlBeanFactory(classPathResource);
    Object testBean = factory.getBean("testBean");
    System.out.println(testBean);
  }
}

先查看XmlBeanfactory继承关系图,观察其有什么功能,再进入步深入源码分析。
《spring 源码-beans(一)》

public class XmlBeanFactory extends DefaultListableBeanFactory {
    //根据名称,可以猜测,该类的作用是读取xml定义的bean
    private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);


    /** * Create a new XmlBeanFactory with the given resource, * which must be parsable using DOM. * @param resource XML resource to load bean definitions from * @throws BeansException in case of loading or parsing errors */
    public XmlBeanFactory(Resource resource) throws BeansException {
        this(resource, null);
    }

    /** * Create a new XmlBeanFactory with the given input stream, * which must be parsable using DOM. * @param resource XML resource to load bean definitions from * @param parentBeanFactory parent bean factory * @throws BeansException in case of loading or parsing errors */
    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
        super(parentBeanFactory);
        this.reader.loadBeanDefinitions(resource);
    }

}

上面的类非常简单,主要作用是DefaultListBeanFactory去实现了,上面可以看到beanfactory已经被XmlBeandefinitionReader 引用,接下来看XmlBeandefinitonReader把xml加载到解释成beandefinition然后再注册到beanfactory里;

3 XmlBeandefinitionReader加载xml配置文件

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

    /** * Load bean definitions from the specified XML file. * @param encodedResource the resource descriptor for the XML file, * allowing to specify an encoding to use for parsing the file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */
    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());
        }
        //本地线程存储当前加载的xml资源
        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 {

            InputStream inputStream = encodedResource.getResource().getInputStream();
            try { //xml文件转为输入流
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //加载读取流资源
                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();
            }
        }
    }

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
    throws BeanDefinitionStoreException {
    try {   //xml转为doc
            Document doc = doLoadDocument(inputSource, resource);
            //接下来就是把xml标签元素解出来,并封装成beandefinition
            return registerBeanDefinitions(doc, resource);
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
    }   

4 解释xml

    //这段代码非常简单无必解释
    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;
    }

接下来是对BeanDefinitionDocumentReader的分析了

    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        doRegisterBeanDefinitions(root);
    }
    /** * Register each bean definition within the given root {@code <beans/>} element. */
    protected void doRegisterBeanDefinitions(Element root) {
        //创建代理解释器
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(getReaderContext(), root, parent);
        //处理不同profile相关
        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;
                }
            }
        }
        //空的,由子类去实现
        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);
        //空的,由子类去实现
        postProcessXml(root);
        this.delegate = parent;
    }
     */
    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        //默认的命名空间http://www.springframework.org/schema/beans
        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)) {
                        //为spring默认标签
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        //自定义标签,深入为自定义标签解释器处理
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
        //自定义标签,深入为自定义标签解释器处理
            delegate.parseCustomElement(root);
        }
    }

5 spring默认标签解释

DefaultBeanDefinitionDocumentReader

    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //import标签 
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            //处理import,xml文件
            importBeanDefinitionResource(ele);
        }
        //alias标签
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            //处理别bean的别名
            processAliasRegistration(ele);
        }
        //bean标签
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            //解释成beandefiniton
            processBeanDefinition(ele, delegate);
        }
        //beans标签
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse beans标签,再进入子元素解释
            doRegisterBeanDefinitions(ele);
        }
    }

    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
    //通过BeanDefinitionParserDelegate 解释成 相应用的 beandefinition 现封装一层成beandefinitionholder
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
//把上面解释得到的beandefinition注册到beanfactory里 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));
        }
    }

BeanDefinitionParserDelegate

    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        //获取id属性值
        String id = ele.getAttribute(ID_ATTRIBUTE);
        //获取名称属性值,可能有多个名称
        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

        List<String> aliases = new ArrayList<String>();
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            aliases.addAll(Arrays.asList(nameArr));
        }

        String beanName = id;
        if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
            beanName = aliases.remove(0);
            if (logger.isDebugEnabled()) {
                logger.debug("No XML 'id' specified - using '" + beanName +
                        "' as bean name and " + aliases + " as aliases");
            }
        }
        //检测名称的唯一性
        if (containingBean == null) {
            checkNameUniqueness(beanName, aliases, ele);
        }
        //开始具体的属性解释,并创建对应的beandefinition
        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(
                                beanDefinition, this.readerContext.getRegistry(), true);
                    }
                    else {
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        // Register an alias for the plain bean class name, if still possible,
                        // if the generator returned the class name plus a suffix.
                        // This is expected for Spring 1.2/2.0 backwards compatibility.
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null &&
                                beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                                !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("Neither XML 'id' nor 'name' specified - " +
                                "using generated bean name [" + beanName + "]");
                    }
                }
                catch (Exception ex) {
                    error(ex.getMessage(), ele);
                    return null;
                }
            }
            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        }

        return null;
    }
    public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {

        this.parseState.push(new BeanEntry(beanName));

        String className = null;
        //解释class属性
        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
        }

        try {//解释parent属性
            String parent = null;
            if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
                parent = ele.getAttribute(PARENT_ATTRIBUTE);
            }
            AbstractBeanDefinition bd = createBeanDefinition(className, parent);
            //解释其余所有属笥
            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
            //解释meta属性
            parseMetaElements(ele, bd);
            //复写属性
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            //替换子元素
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            //处理构造,以便生成实例
            parseConstructorArgElements(ele, bd);
            //处理property 标签
            parsePropertyElements(ele, bd);
            parseQualifierElements(ele, bd);

            bd.setResource(this.readerContext.getResource());
            bd.setSource(extractSource(ele));

            return bd;
        }
        catch (ClassNotFoundException ex) {
            error("Bean class [" + className + "] not found", ele, ex);
        }
        catch (NoClassDefFoundError err) {
            error("Class that bean class [" + className + "] depends on not found", ele, err);
        }
        catch (Throwable ex) {
            error("Unexpected failure during bean definition parsing", ele, ex);
        }
        finally {
            this.parseState.pop();
        }

        return null;
    }

6 自定义标签解释

上面说到的只是默认标签的解释,下面接着自定义标签解释分析
BeanDefinitionParserDelegate

    public BeanDefinition parseCustomElement(Element ele) {
        return parseCustomElement(ele, null);
    }

    public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
        //获取取自定义标签的命名空间uri,能便通过其它对应的命名空间处理器
        String namespaceUri = getNamespaceURI(ele);
        //获取命名空间处理器
        NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
        if (handler == null) {
            error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
            return null;
        }
        //由自定义命名空间处理去解释自定议标签,具体如何释待分析context去分解
        return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
    }

NamespaceHandlerSupport

    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        return findParserForElement(element, parserContext).parse(element, parserContext);
    }

    /** * Locates the {@link BeanDefinitionParser} from the register implementations using * the local name of the supplied {@link Element}. */
    private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
        //据元素名,把到对应的标签解释器
        String localName = parserContext.getDelegate().getLocalName(element);
        BeanDefinitionParser parser = this.parsers.get(localName);
        if (parser == null) {
            parserContext.getReaderContext().fatal(
                    "Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
        }
        return parser;
    }
    原文作者:Spring Boot
    原文地址: https://blog.csdn.net/yangyangiud/article/details/79811436
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
点赞