Spring实现读取配置文件的方法

本篇内容介绍了"Spring实现读取配置文件的方法"的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！

1、XMLBeanFcatory

BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));public class XmlBeanFactory extends DefaultListableBeanFactory {   //核心代码,XmlBeanFactory中使用了自定义的XmlBeanDefinitionReader读取XML文件   XmlBeanDefinitionReader reader = new  XmlBeanDefinitionReader(this);   public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory){      //读取XML配置文件的核心代码      this.reader.loadBeanDefinitions(resource);   }}

2、配置文件封装

加载资源文件可以使用Spring提供的类，如

Resource resource = new ClassPathResource("beanFactory.xml");//getInputStream是在InputStreamResource中定义的唯一方法,它也是Spring对资源封装的最上层接口InputStream inputStream = resource.getInputStream();

public interface InputStreamSource {   InputStream getInputStream() throws IOException;}public interface Resource extends InputStreamSource {   boolean exists();   boolean isReadable();   boolean isOpen();   URL getURL() throws IOException;   URI getURI() throws IOException;   File getFile() throws IOException;   long contentLength() throws IOException;   long lastModified() throws IOException;   Resource createRelative(String relativePath) throws IOException;   String getFilename();   String getDescription();}

3、加载资源文件

当使用new ClassPathResource将资源文件封装为Resource之后，就可以使用XmlBeanDefinitionReader来读取配置文件。

BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory){   this.reader.loadBeanDefinitions(resource);}public int loadBeanDefinitions(Resource resource){   //EncodedResource主要用于对资源文件的编码处理的   return loadBeanDefinitions(new EncodedResource(resource));}public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {   //通过Set来记录已经加载的资源,它是放在ThreadLocal中   Set currentResources = resourcesCurrentlyBeingLoaded.get();   if (currentResources == null) {      currentResources = new HashSet(4);      //放入ThreadLocal中      this.resourcesCurrentlyBeingLoaded.set(currentResources);   }   if (!currentResources.add(encodedResource)) {      throw new BeanDefinitionStoreException();   }   try {      //获取文件输入流,上面已经分析过      InputStream inputStream = encodedResource.getResource().getInputStream();      try {         InputSource inputSource = new InputSource(inputStream);         if (encodedResource.getEncoding() != null) {            inputSource.setEncoding(encodedResource.getEncoding());         }         //真正进入读取的逻辑核心部分,此处传入的inputSource是org.xml.sax.InputResource,用于sax解析         return doLoadBeanDefinitions(inputSource, encodedResource.getResource());   }}protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource){   try {      //步骤1,获取XML文件的验证模式,Spring用来校验验证模式的方法就是判断是否包含DOCTYPE,如果包含就是DTD,否则就是XSD        int validationMode = getValidationModeForResource(resource);      //步骤2,加载XML文件,并得到对应的Document      Document doc = this.documentLoader.loadDocument(                              inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());            //步骤3,根据返回的Document注册Bean信息      return registerBeanDefinitions(doc, resource);   }}//步骤2public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,      ErrorHandler errorHandler, int validationMode, boolean namespaceAware){   //SAX解析XML文档,返回Document对象   DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);     DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);   return builder.parse(inputSource);}//步骤3public int registerBeanDefinitions(Document doc, Resource resource) {   BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();   //设置环境变量   documentReader.setEnvironment(this.getEnvironment());   //记录之前BeanDefinition中定义的Bean的数量   int countBefore = getRegistry().getBeanDefinitionCount();   documentReader.registerBeanDefinitions(doc, createReaderContext(resource));   //返回本次加载的BeanDefinition个数   return getRegistry().getBeanDefinitionCount() - countBefore;}

4、开始解析

documentReader.registerBeanDefinitions(doc, createReaderContext(resource));public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext){   this.readerContext = readerContext;   //读取的根元素,debug时显示为[beans: null]   Element root = doc.getDocumentElement();   doRegisterBeanDefinitions(root);}protected void doRegisterBeanDefinitions(Element root) {   //处理profile元素,profile标签可以用于配置生产环境、开发环境等   String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);   if (StringUtils.hasText(profileSpec)) {      Assert.state(this.environment != null, "Environment must set for evaluating profiles");      String[] specifiedProfiles                  = StringUtils.tokenizeToStringArray(profileSpec,                                                       BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);      if (!this.environment.acceptsProfiles(specifiedProfiles)) {         return;      }   }   //专门处理解析的代理   BeanDefinitionParserDelegate parent = this.delegate;   this.delegate = createDelegate(this.readerContext, root, parent);      //此处的两个方法为空实现,面向继承设计,这是模板方法模式,子类可以继承并在解析前做一些处理   preProcessXml(root);   parseBeanDefinitions(root, this.delegate);   postProcessXml(root);   this.delegate = parent;}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)) {               //解析默认标签,如bean               parseDefaultElement(ele, delegate);            }            else {               //解析自定义标签,如               delegate.parseCustomElement(ele);            }         }      }   }   else {      delegate.parseCustomElement(root);   }}

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