Spring Ioc 的源码初识

          刚学习Spring的时候，印象最深的就是 DispatcherServlet，所谓的中央调度器，我也尝试从这个万能胶这里找到入口

        configureAndRefreshWebApplicationContext()方法，应该就是IOC容器初始化的真正入口

        我开始手写测试用例(xml配置的bean实例)，ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("xxx.xml");

        通过跟踪代码和debug的方式，找到了大概的初始化流程

       

ClassPathXmlApplicationContext 的构造方法

    public ClassPathXmlApplicationContext(String configLocation) 
   throws BeansException {
        this(new String[] {configLocation}, true, null);
    }

AbstractApplicationContext类

        接着--->>>

       

接着--->>>AbstractXmlApplicationContext

        protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        //创建XmlBeanDefinitionReader
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        beanDefinitionReader.setEnvironment(this.getEnvironment());
        //容器本身也是一个资源加载器
        beanDefinitionReader.setResourceLoader(this);
        //为Bean读取器设置SAX xml解析器
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

        //当Bean读取器读取Bean定义的Xml资源文件时，启用Xml的校验机制
        initBeanDefinitionReader(beanDefinitionReader);
        //Bean读取器真正实现加载的方法
        loadBeanDefinitions(beanDefinitionReader);
            }


        protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        //获取Bean定义资源的定位
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
        //如果子类中获取的Bean定义资源定位为空，则获取FileSystemXmlApplicationContext构造方法中setConfigLocations方法设置的资源
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            //Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位
            reader.loadBeanDefinitions(configLocations);
        }
            }

接着--->>>AbstractBeanDefinitionReader

    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
        Assert.notNull(locations, "Location array must not be null");
        int counter = 0;
        for (String location : locations) {
            counter += loadBeanDefinitions(location);
        }
        return counter;
           }

接着--->>>

  public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException { return loadBeanDefinitions(location, null); } 

接着--->>>

    public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        //获取在IoC容器初始化过程中设置的资源加载器
        ResourceLoader resourceLoader = getResourceLoader();
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        }

        if (resourceLoader instanceof ResourcePatternResolver) {
            try {
                //加载多个指定位置的Bean定义资源文件
                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                //委派调用其子类XmlBeanDefinitionReader的方法，实现加载功能
                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 {
            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;
        }
          }

接着--->>>

       public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
        Assert.notNull(resources, "Resource array must not be null");
        int counter = 0;
        for (Resource resource : resources) {
            counter += loadBeanDefinitions(resource);
        }
        return counter;
           }

接着--->>>XmlBeanDefinitionReader

      public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        //将读入的XML资源进行特殊编码处理
        return loadBeanDefinitions(new EncodedResource(resource));
           }

接着--->>>

    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<>(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        try {
            //将资源文件转为InputStream的IO流
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                //从InputStream中得到XML的解析源
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //这里是具体的读取过程
                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();
            }
        }
           }

接着--->>>

       protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            //将XML文件转换为DOM对象，解析过程由documentLoader实现
            Document doc = doLoadDocument(inputSource, resource);
            //这里是启动对Bean定义解析的详细过程，该解析过程会用到Spring的Bean配置规则
            return registerBeanDefinitions(doc, resource);
        }
        catch (Exception ex) {
            throw ex;
        }}

接着--->>> 

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //获取BeanDefinitionDocumentReader
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        //获得容器中注册的Bean数量
        int countBefore = getRegistry().getBeanDefinitionCount();
        //具体的解析实现过程实现类DefaultBeanDefinitionDocumentReader完成
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        //统计解析的Bean数量
        return getRegistry().getBeanDefinitionCount() - countBefore;
            }

接着--->>>DefaultBeanDefinitionDocumentReader

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        //获得XML描述符
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        //获得Document的根元素
        Element root = doc.getDocumentElement();
        doRegisterBeanDefinitions(root);
            }

接着--->>>

        protected void doRegisterBeanDefinitions(Element root) {
        //具体的解析过程由BeanDefinitionParserDelegate实现，
        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;}}}
        //在解析Bean定义之前，进行自定义的解析，增强解析过程的可扩展性
        preProcessXml(root);
        //从Document的根元素开始进行Bean定义的Document对象
        parseBeanDefinitions(root, this.delegate);
        //在解析Bean定义之后，进行自定义的解析，增加解析过程的可扩展性
        postProcessXml(root);
        this.delegate = parent;
    }

接着--->>>

    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        //Bean定义的Document对象使用了Spring默认的XML命名空间
        if (delegate.isDefaultNamespace(root)) {
            NodeList nl = root.getChildNodes();
            for (int i = 0; i < nl.getLength(); i++) {
                Node node = nl.item(i);
                //获得Document节点是XML元素节点
                if (node instanceof Element) {
                    Element ele = (Element) node;
                    //Bean定义的Document的元素节点使用的是Spring默认的XML命名空间
                    if (delegate.isDefaultNamespace(ele)) {
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
          }

接着--->>>

          private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //如果元素节点是<Import>导入元素，进行导入解析
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        //如果元素节点是<Alias>别名元素，进行别名解析
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        //按照Spring的Bean规则解析元素
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
            }

接着--->>>

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        // BeanDefinitionHolder是对BeanDefinition的封装，即Bean定义的封装类
        // BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                //向Spring IOC容器注册解析得到的Bean定义，这是Bean定义向IOC容器注册的入口
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +bdHolder.getBeanName() + "'", ele, ex);
            }
            //在完成向Spring IOC容器注册解析得到的Bean定义之后，发送注册事件
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
             }

接着--->>>BeanDefinitionReaderUtils

public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {
        //获取解析的BeanDefinition的名称
        String beanName = definitionHolder.getBeanName();
        //向IOC容器注册BeanDefinition
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

        //如果解析的BeanDefinition有别名，向容器为其注册别名
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
           }