在该文中来讲讲Spring框架中BeanFactory解析bean的过程,该文之前在小编原文中有发表过,先来看一个在Spring中一个基本的bean定义与使用。
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package bean; public class TestBean { private String beanName = "beanName" ; public String getBeanName() { return beanName; } public void setBeanName(String beanName) { this .beanName = beanName; } } |
Spring配置文件root.xml定义如下:
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<? xml version = "1.0" encoding = "UTF-8" ?> < beans xmlns = "http://www.springframework.org/schema/beans" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd"> < bean id = "testBean" class = "bean.TestBean" > </ beans > |
下面使用XmlBeanFactory来获取该bean:
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public class BeanTest { private static final java.util.logging.Logger logger = LoggerFactory.getLogger(BeanTest. class ); @Test public void getBeanTest() { BeanFactory factory = new XmlBeanFactory( new ClassPathResource( "root.xml" )); TestBean bean = factory.getBean( "testBean" ); logger.info(bean.getBeanName); } } |
这个单元测试运行结果就是输出beanName,上面就是Spring最基本的bean的获取操作,这里我用BeanFactory作为容器来获取bean的操作并不多见,在企业开发中一般是使用功能更完善的ApplicationContext,这里先不讨论这个,下面重点讲解使用BeanFactory获取bean的过程。
现在就来分析下上面的测试代码,看看Spring到底为我们做了什么工作,上面代码完成功能的流程不外乎如此:
1. 读取Spring配置文件root.xml;
2. 根据root.xml中的bean配置找到对应的类的配置,并实例化;
3. 调用实例化后的对象输出结果。
先来看看XmlBeanFactory源码:
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public class XmlBeanFactory extends DefaultListableBeanFactory { private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader( this ); public XmlBeanFactory(Resource resource) throws BeansException { this (resource, null ); } public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException { super (parentBeanFactory); this .reader.loadBeanDefinitions(resource); } } |
从上面可以看出XmlBeanFactory继承了DefaultListableBeanFactory,DefaultListableBeanFactory是Spring注册加载bean的默认实现,它是整个bean加载的核心部分,XmlBeanFactory与它的不同点就是XmlBeanFactory使用了自定义的XML读取器XmlBeanDefinitionReader,实现了自己的BeanDefinitionReader读取。
XmlBeanFactory加载bean的关键就在于XmlBeanDefinitionReader,下面看看XmlBeanDefinitionReader的源码(只列出部分):
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public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader { private Class<?> documentReaderClass = DefaultBeanDefinitionDocumentReader. class ; private ProblemReporter problemReporter = new FailFastProblemReporter(); private ReaderEventListener eventListener = new EmptyReaderEventListener(); private SourceExtractor sourceExtractor = new NullSourceExtractor(); private NamespaceHandlerResolver namespaceHandlerResolver; private DocumentLoader documentLoader = new DefaultDocumentLoader(); private EntityResolver entityResolver; private ErrorHandler errorHandler = new SimpleSaxErrorHandler(logger); } |
XmlBeanDefinitionReader继承自AbstractBeanDefinitionReader,下面是AbstractBeanDefinitionReader的源码(只列出部分):
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public abstract class AbstractBeanDefinitionReader implements EnvironmentCapable, BeanDefinitionReader { protected final Log logger = LogFactory.getLog(getClass()); private final BeanDefinitionRegistry registry; private ResourceLoader resourceLoader; private ClassLoader beanClassLoader; private Environment environment; private BeanNameGenerator beanNameGenerator = new DefaultBeanNameGenerator(); } |
XmlBeanDefinitionReader主要通过以下三步来加载Spring配置文件中的bean:
1. 通过继承自AbstractBeanDefinitionReader中的方法,使用ResourLoader将资源文件(root.xml)路径转换为对应的Resource文件;
2. 通过DocumentLoader对Resource文件进行转换,将Resource文件转换为Ducument文件;
3. 通过DefaultBeanDefinitionDocumentReader类对Document进行解析,最后再对解析后的Element进行解析。
了解以上基础后,接下来详细分析下一开始例子中的代码:
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BeanFactory factory = new XmlBeanFactory( new ClassPathResource( "root.xml" )); |
先看看下面XmlBeanFactory初始化的时序图来进一步了解这段代码的执行,
在这里可以看出BeanTest测试类通过向ClassPathResource的构造方法传入spring的配置文件构造一个Resource资源文件的实例对象,再通过这个Resource资源文件来构造我们想要的XmlBeanFactory实例。在前面XmlBeanFactory源码中的构造方法可以看出,
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public XmlBeanFactory(Resource resource) throws BeansException { this (resource, null ); } public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException { super (parentBeanFactory); this .reader.loadBeanDefinitions(resource); } |
this.reader.loadBeanDefinition(resource)就是资源加载真正的实现,时序图中XmlBeanDefinitionReader加载数据就是在这里完成的。
接下来跟进this.reader.loadBeanDefinition(resource)方法里面,
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public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader { @Override public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { return loadBeanDefinitions( new EncodedResource(resource)); } } |
在loadBeanDefinition(resource)方法里对资源文件resource使用EncodedResource进行编码处理后继续传入loadBeanDefinitions方法,继续跟进loadBeanDefinitions(new EncodedResource(resource))方法源码:
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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<EncodedResource>( 4 ); this .resourcesCurrentlyBeingLoaded.set(currentResources); } if (!currentResources.add(encodedResource)) { throw new BeanDefinitionStoreException( "Detected cyclic loading of " + encodedResource + " - check your import definitions!" ); } try { // 从resource中获取对应的InputStream,用于下面构造InputSource InputStream inputStream = encodedResource.getResource().getInputStream(); try { InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null ) { inputSource.setEncoding(encodedResource.getEncoding()); } // 调用doLoadBeanDefinitions方法 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(); } } } |
继续跟进doLoadBeanDefinitions(inputSource, encodedResource.getResource())方法,这是整个bean加载过程的核心方法,在这个方法执行bean的加载。
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protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { Document doc = doLoadDocument(inputSource, resource); return registerBeanDefinitions(doc, resource); } /* 省略一堆catch */ } |
跟进doLoadDocument(inputSource, resource)源码:
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protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception { return this .documentLoader.loadDocument(inputSource, getEntityResolver(), this .errorHandler, getValidationModeForResource(resource), isNamespaceAware()); } |
在doLoadDocument(inputSource, resource)方法里就使用到了前面讲的documentLoader加载Document,这里DocumentLoader是个接口,真正调用的是其实现类DefaultDocumentLoader的loadDocument方法,跟进源码:
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public class DefaultDocumentLoader implements DocumentLoader { @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); } } |
从源码可以看出这里先创建DocumentBuilderFactory,再用它创建DocumentBuilder,进而解析inputSource来返回Document对象。得到Document对象后就可以准备注册我们的Bean信息了。
在上面的doLoadBeanDefinitions(inputSource, encodedResource.getResource())方法中拿到Document对象后下面就是执行registerBeanDefinitions(doc, resource)方法了,看源码:
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public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader(); documentReader.setEnvironment(getEnvironment()); // 还没注册bean前的BeanDefinition加载个数 int countBefore = getRegistry().getBeanDefinitionCount(); // 加载注册bean documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); // 本次加载注册的BeanDefinition个数 return getRegistry().getBeanDefinitionCount() - countBefore; } |
这里的doc就是上面的loadDocument方法加载转换来的,从上面可以看出主要工作是交给BeanDefinitionDocumentReader的registerBeanDefinitions()方法实现的,这里BeanDefinitionDocumentReader是个接口,注册bean功能在默认实现类DefaultBeanDefinitionDocumentReader的该方法实现,跟进它的源码:
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@Override public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this .readerContext = readerContext; logger.debug( "Loading bean definitions" ); Element root = doc.getDocumentElement(); doRegisterBeanDefinitions(root); } |
到这里通过doc.getDocumentElement()获得Element对象后,交给doRegisterBeanDefinitions()方法后就是真正执行XML文档的解析了,跟进doRegisterBeanDefinitions()方法源码:
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protected void doRegisterBeanDefinitions(Element root) { 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)) { return ; } } } preProcessXml(root); parseBeanDefinitions(root, this .delegate); postProcessXml(root); this .delegate = parent; } |
到这里处理流程就很清晰了,先是对profile进行处理,之后就通过parseBeanDefinitions()方法进行文档的解析操作,跟进parseBeanDefinitions()方法源码:
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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; // 下面对bean进行处理 if (delegate.isDefaultNamespace(ele)) { parseDefaultElement(ele, delegate); } else { delegate.parseCustomElement(ele); } } } } else { delegate.parseCustomElement(root); } } |
上面if-else语句块中的parseDefaultElement(ele, delegate)和delegate.parseCustomElement(ele)就是对Spring配置文件中的默认命名空间和自定义命名空间进行解析用的。在Spring的XML配置中,默认Bean声明就如前面定义的:
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< bean id = "testBean" class = "bean.TestBean" > |
自定义的Bean声明如:
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< tx:annotation-driven /> |
XmlBeanFactory加载bean的整个过程基本就讲解到这里了。希望对大家的学习有所帮助,也希望大家多多支持服务器之家。
原文链接:http://www.cnblogs.com/weknow619/p/6667392.html