spring加载xml配置文件的源码分析

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1 将资源文件封装成Resource

如Resource re = new ClassPathResource(“”);

  1. 将加载好的资源文件 通过XmlBeanFactory初始化

    public class XmlBeanFactory extends DefaultListableBeanFactory {

        private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);

        public XmlBeanFactory(Resource resource) throws BeansException {
            this(resource, null);
        }

           /**  该方法为资源加载的真正实现*/
        public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
            super(parentBeanFactory);
            this.reader.loadBeanDefinitions(resource);
        }

    }

3.加载bean


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

首先使用EncodedResource对resource进行封装,当设置了编码属性,spring会使用相应的编码作为输入流的编码


    private EncodedResource(Resource resource, String encoding, Charset charset) {
            super();
            Assert.notNull(resource, "Resource must not be null");
            this.resource = resource;
            this.encoding = encoding;
            this.charset = charset;
        }

    public Reader getReader() throws IOException {
            if (this.charset != null) {
                return new InputStreamReader(this.resource.getInputStream(), this.charset);
            }
            else if (this.encoding != null) {
                return new InputStreamReader(this.resource.getInputStream(), this.encoding);
            }
            else {
                return new InputStreamReader(this.resource.getInputStream());
            }
        }

上述代码构建好了一个有编码的InputStreamReader

下面这个方法才是真正的数据准备阶段


    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 {
                InputStream inputStream = encodedResource.getResource().getInputStream();
                try {
                    InputSource inputSource = new InputSource(inputStream);
                    if (encodedResource.getEncoding() != null) {
                        inputSource.setEncoding(encodedResource.getEncoding());
                    }
                                   /**真正的核心逻辑**/
                    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();
                }
            }
        }

    //通过属性记录已经加载的资源,放入Threadlocal变量中
        private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded =new NamedThreadLocal<Set<EncodedResource>>("XML bean definition resources currently being loaded");

    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);
            }
        }

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

    //获取验证模式(DTD XSD两种验证模式)
    protected int getValidationModeForResource(Resource resource) {
            int validationModeToUse = getValidationMode();
                     //如果手动指定了验证模式则使用指定的验证模式
            if (validationModeToUse != VALIDATION_AUTO) {
                return validationModeToUse;
            }
                    //没有指定 则使用自动检测
            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;
        }

    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;
        }

    此段代码 主要做了三件事:
         获取对xml文件的验证模式
         加载xml文件,并得到对应的Document
         根据返回的Document注册Bean的信息

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