Spring源码学习--容器的基础XmlBeanFactory(加载Bean)

继上文Spring源码学习–容器的基础XmlBeanFactory(加载Bean)

https://blog.csdn.net/u013412772/article/details/80048603

继续分析下面这行代码的运行过程:

BeanFactory beanFactory = new XmlBeanFactory(new ClassPathResource(“beanFactoryTest.xml”));

在XMLBeanFactory构造方法XmlBeanFactory(Resource resource):

@Deprecated
@SuppressWarnings({"serial", "all"})
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);
    }

}

跟着this.reader.loadBeanDefinitions(resource);进入XmlBeanDefinitionReader类型的reader属性提供的loadBeanDefinitions(Resource resource)方法.this.reader.loadBeanDefinitions(resource);这行代码是整个资源加载的切入点,先来看一下调用时序图:

从上面时序图中可以得知,在加载XML文档和解析注册Bean,一直在做准备工作.依据上面的时序图来分析一下这里究竟在做什么准备?

封装资源文件.当进入XmlBeanDefinitionReader后首先对参数Resource使用EncodedResource类进行封装
获取输入流.从Resource中获取对应的InputStream并构造InputSource.
通过构造的InputSource实例和Resource实例继续调用函数doLoadBeanDefinitions

接下来看一下loadBeanDefinitions函数具体的实现过程:

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

其中EncodedResource的作用:对资源文件的编码进行处理.其中的主要逻辑体现在getReader方法中,当设置了编码属性的时候Spring会使用相应的编码作为输入流的编码.其中getReader方法如下:

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());
    }
}

上面的代码中构造了一个由编码(encoding)的InputStreamReader.当构造好EncodedResource对象后,再次转入了可复用方法loadBeanDefinitions(EncodedResource encodedResource).

这个方法内部才是真正的数据准备阶段,也就是时序图所描述的逻辑:

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());
    }

    // 通过属性来记录已经加载的资源
    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EncodedResource中获取已经封装的Resource对象并再次从Resource中获取其中的inputStream
        InputStream inputStream = encodedResource.getResource().getInputStream();
        try {
            // InputSource这个类并不是来源于Spring，他的全路径为：org.xml.sax.InputSource
            InputSource inputSource = new InputSource(inputStream);
            if (encodedResource.getEncoding() != null) {
                inputSource.setEncoding(encodedResource.getEncoding());
            }

            // 真正进入了逻辑核心服务
            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();
        }
    }
}

整理一下上面的逻辑:首先对resource参数做封装,目的是考虑到Resource可能存在编码要求的情况,其次,通过SAX读取XML文件的方式来准备InputSource对象,最后将准备的数据通过参数传入真正的核心处理部分doLoadBeanDefinitions(inputSource, encodedResource.getResource()).其中doLoadBeanDefinitions(inputSource, encodedResource.getResource())方法实现如下:

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);
    }
}

忽略掉上面的异常处理部分,上面的代码只做了三件事情:

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信息.

上面的三个步骤支撑着整个Spring容器部分的实现基础.

Spring源码学习--容器的基础XmlBeanFactory(加载Bean)

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