通过xml文件加载BeanDefinition

# 通过xml文件加载BeanDefinition

# BeanDefinition的资源定位过程

# ClassPathXmlApplicationContext

该方式使用ClassPathXmlApplicationContext来创建Spring容器

ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");

ClassPathXmlApplicationContext类的UML图如下：

ClassPathXmlApplicationContext继承了AbstractRefreshableApplicationContext

AbstractApplicationContext#refresh在刷新容器的第二步AbstractApplicationContext#obtainFreshBeanFactory方法中会执行到AbstractRefreshableApplicationContext#refreshBeanFactory

protected final void refreshBeanFactory() throws BeansException {
    if (hasBeanFactory()) {
        destroyBeans();
        closeBeanFactory();
    }
    try {
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        beanFactory.setSerializationId(getId());
        customizeBeanFactory(beanFactory);
        loadBeanDefinitions(beanFactory);
        this.beanFactory = beanFactory;
    }
    catch (IOException ex) {
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

loadBeanDefinitions既是加载BeanDefinition的方法

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
    // Create a new XmlBeanDefinitionReader for the given BeanFactory.
    XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

    // Configure the bean definition reader with this context's
    // resource loading environment.
    beanDefinitionReader.setEnvironment(this.getEnvironment());
    beanDefinitionReader.setResourceLoader(this);
    beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

    // Allow a subclass to provide custom initialization of the reader,
    // then proceed with actually loading the bean definitions.
    initBeanDefinitionReader(beanDefinitionReader);
    loadBeanDefinitions(beanDefinitionReader);
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

将环境配置封装到XmlBeanDefinitionReader，委托该类进行加载

# XmlBeanDefinitionReader

XmlBeanDefinitionReader继承AbstractBeanDefinitionReader

AbstractBeanDefinitionReader#loadBeanDefinitions的模板方法

public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
    ResourceLoader resourceLoader = getResourceLoader();
    if (resourceLoader == null) {
        throw new BeanDefinitionStoreException(
                "Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
    }

    if (resourceLoader instanceof ResourcePatternResolver) {
        // Resource pattern matching available.
        try {
            //根据配置文件路径获取配置资源
            Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
            int count = loadBeanDefinitions(resources);
            if (actualResources != null) {
                Collections.addAll(actualResources, resources);
            }
            return count;
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(
                    "Could not resolve bean definition resource pattern [" + location + "]", ex);
        }
    }
    else {
        // Can only load single resources by absolute URL.
        Resource resource = resourceLoader.getResource(location);
        int count = loadBeanDefinitions(resource);
        if (actualResources != null) {
            actualResources.add(resource);
        }
        return count;
    }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33

resourceLoader是上一步被封装到XmlBeanDefinitionReader中的ClassPathXmlApplicationContext，从UML图中可以看到它间接实现了ResourcePatternResolver，所以走第一个if分支

最终还会调用到XmlBeanDefinitionReader#doLoadBeanDefinitions

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
		throws BeanDefinitionStoreException {

	try {
        //读取配置资源，生成文档类
		Document doc = doLoadDocument(inputSource, resource);
        //从文档类注册BeanDefinition
		int count = registerBeanDefinitions(doc, resource);
		return count;
	}
    // ...
}

1
2
3
4
5
6
7
8
9
10
11
12

XmlBeanDefinitionReader#registerBeanDefinitions

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;
}

1
2
3
4
5
6

这里又委托给DefaultBeanDefinitionDocumentReader进行解析注册

# DefaultBeanDefinitionDocumentReader

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)) {
            //解析profile，支持多个
			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
					profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			// We cannot use Profiles.of(...) since profile expressions are not supported
			// in XML config. See SPR-12458 for details.
            //如果profile不符合则不解析
			if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
							"] not matching: " + getReaderContext().getResource());
				}
				return;
			}
		}
	}

	preProcessXml(root);
	parseBeanDefinitions(root, this.delegate);
	postProcessXml(root);

	this.delegate = parent;
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

preProcessXml和postProcessXml是留给子类实现的前置处理和后置处理，在DefaultBeanDefinitionDocumentReader中是空实现

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
	if (delegate.isDefaultNamespace(root)) {
        //默认标签解析
		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)) {
                    //默认标签解析
					parseDefaultElement(ele, delegate);
				}
				else {
                    //自定义标签解析
					delegate.parseCustomElement(ele);
				}
			}
		}
	}
	else {
        //自定义标签解析
		delegate.parseCustomElement(root);
	}
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

到这里Spring完成了对于配置文件的资源定位，以及dom解析生成BeanDefinition。对于具体的默认标签解析 (opens new window)和自定义标签解析 (opens new window)后面再详细记录。

编辑

#BeanDefinition

上次更新: 2023/04/09, 16:34:32

← 通过注解加载BeanDefinition xml解析之默认标签解析→