基于Properties文件读取Bean定义

1.bean读取方式一：
Bean配置在内部是通过实习了BeanDefination接口的类实例来表现的，Bean的配置不仅存储了bean自己的信息，而其也体现了bean的依赖信息。对于任何同时实现了beanDefinationRegistery接口的BeanFantory类，你可以通过配置文件中读取Bean定义，通过PropertiesBeanDefinitionReader类就是一种方式。还又另一种方式，下次介绍。
2.看PropertiesBeanDefinitionReader源代码：

public class PropertiesBeanDefinitionReader extends AbstractBeanDefinitionReader {
..............................
}

主要方法：
loadBeanDefinitions();加载bean属性定义从一个properties文件，这个文件资源被封装到一个带编码方式的资源,并按该编码方式解析文件,prefix是过滤的前缀，可以为空。返回取得的bean的数量

public int loadBeanDefinitions(EncodedResource encodedResource, String prefix) throws BeansException {
		Properties props = new Properties();
		try {
			InputStream is = encodedResource.getResource().getInputStream();
			try {
				if (encodedResource.getEncoding() != null) {//运用属性持久器[b]（这里用的是：DefaultPropertiesPersister）[/b]以流的形式，并按制定的编码方式加载bean属性
					getPropertiesPersister().load(props, new InputStreamReader(is, encodedResource.getEncoding()));
				}
				else {//
					getPropertiesPersister().load(props, is);
				}
			}
			finally {//关闭流
				is.close();
			}//调用下面介绍的另一个重要方法，去注册bean
			return registerBeanDefinitions(props, prefix, encodedResource.getResource().getDescription());
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException("Could not parse properties from " + encodedResource.getResource(), ex);
		}
	}

registerBeanDefinitions();解析出bean的名字，让后调用注册方法，注册beanName到工厂，返回注册过的bean的数量

public int registerBeanDefinitions(Map map, String prefix, String resourceDescription)
			throws BeansException {

		if (prefix == null) {
			prefix = "";
		}
		int beanCount = 0;

		for (Iterator it = map.keySet().iterator(); it.hasNext();) {
			Object key = it.next();
			if (!(key instanceof String)) {
				throw new IllegalArgumentException("Illegal key [" + key + "]: only Strings allowed");
			}
			String keyString = (String) key;
			if (keyString.startsWith(prefix)) {
				// Key is of form: prefix<name>.property
				String nameAndProperty = keyString.substring(prefix.length());
				// Find dot before property name, ignoring dots in property keys.
				int sepIdx = -1;
				int propKeyIdx = nameAndProperty.indexOf(PropertyAccessor.PROPERTY_KEY_PREFIX);
				if (propKeyIdx != -1) {
					sepIdx = nameAndProperty.lastIndexOf(SEPARATOR, propKeyIdx);
				}
				else {
					sepIdx = nameAndProperty.lastIndexOf(SEPARATOR);
				}
				if (sepIdx != -1) {
					String beanName = nameAndProperty.substring(0, sepIdx);
					if (logger.isDebugEnabled()) {
						logger.debug("Found bean name '" + beanName + "'");
					}
					if (!getBeanFactory().containsBeanDefinition(beanName)) {
						// If we haven't already registered it...
						registerBeanDefinition(beanName, map, prefix + beanName, resourceDescription);
						++beanCount;
					}
				}
				else {
					// Ignore it: It wasn't a valid bean name and property,
					// although it did start with the required prefix.
					if (logger.isDebugEnabled()) {
						logger.debug("Invalid bean name and property [" + nameAndProperty + "]");
					}
				}
			}
		}

		return beanCount;
	}

registerBeanDefinition();得到bean的所有属性值，并加一前缀，并讲bean注册到工厂

protected void registerBeanDefinition(String beanName, Map map, String prefix, String resourceDescription)
			throws BeansException {
//bean的属性
		String className = null;
		String parent = null;
		boolean isAbstract = false;
		boolean singleton = true;
		boolean lazyInit = false;

		ConstructorArgumentValues cas = new ConstructorArgumentValues();
		MutablePropertyValues pvs = new MutablePropertyValues();

		for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
			Map.Entry entry = (Map.Entry) it.next();
			String key = StringUtils.trimWhitespace((String) entry.getKey());
			if (key.startsWith(prefix + SEPARATOR)) {
				String property = key.substring(prefix.length() + SEPARATOR.length());
				if (isClassKey(property)) {
					className = StringUtils.trimWhitespace((String) entry.getValue());
				}
				else if (PARENT_KEY.equals(property)) {
					parent = StringUtils.trimWhitespace((String) entry.getValue());
				}
				else if (ABSTRACT_KEY.equals(property)) {
					String val = StringUtils.trimWhitespace((String) entry.getValue());
					isAbstract = TRUE_VALUE.equals(val);
				}
				else if (SINGLETON_KEY.equals(property)) {
					String val = StringUtils.trimWhitespace((String) entry.getValue());
					singleton = (val == null) || TRUE_VALUE.equals(val);
				}
				else if (LAZY_INIT_KEY.equals(property)) {
					String val = StringUtils.trimWhitespace((String) entry.getValue());
					lazyInit = TRUE_VALUE.equals(val);
				}
				else if (property.startsWith(CONSTRUCTOR_ARG_PREFIX)) {
					if (property.endsWith(REF_SUFFIX)) {
						int index = Integer.parseInt(property.substring(1, property.length() - REF_SUFFIX.length()));
						cas.addIndexedArgumentValue(index, new RuntimeBeanReference(entry.getValue().toString()));
					}
					else {
						int index = Integer.parseInt(property.substring(1));
						cas.addIndexedArgumentValue(index, readValue(entry));
					}
				}
				else if (property.endsWith(REF_SUFFIX)) {
					// This isn't a real property, but a reference to another prototype
					// Extract property name: property is of form dog(ref)
					property = property.substring(0, property.length() - REF_SUFFIX.length());
					String ref = StringUtils.trimWhitespace((String) entry.getValue());

					// It doesn't matter if the referenced bean hasn't yet been registered:
					// this will ensure that the reference is resolved at runtime.
					Object val = new RuntimeBeanReference(ref);
					pvs.addPropertyValue(property, val);
				}
				else{
					// It's a normal bean property.
					pvs.addPropertyValue(property, readValue(entry));
				}
			}
		}

		if (logger.isDebugEnabled()) {
			logger.debug("Registering bean definition for bean name '" + beanName + "' with " + pvs);
		}

		// Just use default parent if we're not dealing with the parent itself,
		// and if there's no class name specified. The latter has to happen for
		// backwards compatibility reasons.
		if (parent == null && className == null && !beanName.equals(this.defaultParentBean)) {
			parent = this.defaultParentBean;
		}

		try {//这里用解析出的属性，构建一个beanDefination的基类实例
			AbstractBeanDefinition bd = BeanDefinitionReaderUtils.createBeanDefinition(
					parent, className, getBeanClassLoader());
			bd.setAbstract(isAbstract);
			bd.setSingleton(singleton);
			bd.setLazyInit(lazyInit);
			bd.setConstructorArgumentValues(cas);
			bd.setPropertyValues(pvs)；
//这里讲该bean注册到beanFantory
			getBeanFactory().registerBeanDefinition(beanName, bd);
		}
		catch (ClassNotFoundException ex) {
			throw new CannotLoadBeanClassException(resourceDescription, beanName, className, ex);
		}
		catch (LinkageError err) {
			throw new CannotLoadBeanClassException(resourceDescription, beanName, className, err);
		}
	}