Spring源码解析--Spring配置文件解析BeanDefinitionParserDelegate（四）

       上一篇博客Spring源码学习--Spring配置文件解析BeanDefinitionDocumentReader（三）中我们已经了解到对于Spring的配置文件的解析处理操作是在BeanDefinitionParserDelegate中进行处理操作，接下来我们简单介绍一下BeanDefinitionParserDelegate所做的处理操作。

       首先BeanDefinitionParserDelegate中定义了其会解析xml的spring元素标签，并且还有说明一点的是Spring解析xml的标签是通过命名空间Namespace来决定的，BeanDefinitionParserDelegate中定义了如下命名空间，只会支持解析这个命名空间中的标签元素。

public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";

BeanDefinitionParserDelegate中定义的spring的标签元素如下：

public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";public static final String MULTI_VALUE_ATTRIBUTE_DELIMITERS = ",; ";public static final String TRUE_VALUE = "true";public static final String FALSE_VALUE = "false";public static final String DEFAULT_VALUE = "default";public static final String DESCRIPTION_ELEMENT = "description";public static final String AUTOWIRE_NO_VALUE = "no";public static final String AUTOWIRE_BY_NAME_VALUE = "byName";public static final String AUTOWIRE_BY_TYPE_VALUE = "byType";public static final String AUTOWIRE_CONSTRUCTOR_VALUE = "constructor";public static final String AUTOWIRE_AUTODETECT_VALUE = "autodetect";public static final String DEPENDENCY_CHECK_ALL_ATTRIBUTE_VALUE = "all";public static final String DEPENDENCY_CHECK_SIMPLE_ATTRIBUTE_VALUE = "simple";public static final String DEPENDENCY_CHECK_OBJECTS_ATTRIBUTE_VALUE = "objects";public static final String NAME_ATTRIBUTE = "name";public static final String BEAN_ELEMENT = "bean";public static final String META_ELEMENT = "meta";public static final String ID_ATTRIBUTE = "id";public static final String PARENT_ATTRIBUTE = "parent";public static final String CLASS_ATTRIBUTE = "class";public static final String ABSTRACT_ATTRIBUTE = "abstract";public static final String SCOPE_ATTRIBUTE = "scope";private static final String SINGLETON_ATTRIBUTE = "singleton";public static final String LAZY_INIT_ATTRIBUTE = "lazy-init";public static final String AUTOWIRE_ATTRIBUTE = "autowire";public static final String AUTOWIRE_CANDIDATE_ATTRIBUTE = "autowire-candidate";public static final String PRIMARY_ATTRIBUTE = "primary";public static final String DEPENDENCY_CHECK_ATTRIBUTE = "dependency-check";public static final String DEPENDS_ON_ATTRIBUTE = "depends-on";public static final String INIT_METHOD_ATTRIBUTE = "init-method";public static final String DESTROY_METHOD_ATTRIBUTE = "destroy-method";public static final String FACTORY_METHOD_ATTRIBUTE = "factory-method";public static final String FACTORY_BEAN_ATTRIBUTE = "factory-bean";public static final String CONSTRUCTOR_ARG_ELEMENT = "constructor-arg";public static final String INDEX_ATTRIBUTE = "index";public static final String TYPE_ATTRIBUTE = "type";public static final String VALUE_TYPE_ATTRIBUTE = "value-type";public static final String KEY_TYPE_ATTRIBUTE = "key-type";public static final String PROPERTY_ELEMENT = "property";public static final String REF_ATTRIBUTE = "ref";public static final String VALUE_ATTRIBUTE = "value";public static final String LOOKUP_METHOD_ELEMENT = "lookup-method";public static final String REPLACED_METHOD_ELEMENT = "replaced-method";public static final String REPLACER_ATTRIBUTE = "replacer";public static final String ARG_TYPE_ELEMENT = "arg-type";public static final String ARG_TYPE_MATCH_ATTRIBUTE = "match";public static final String REF_ELEMENT = "ref";public static final String IDREF_ELEMENT = "idref";public static final String BEAN_REF_ATTRIBUTE = "bean";public static final String LOCAL_REF_ATTRIBUTE = "local";public static final String PARENT_REF_ATTRIBUTE = "parent";public static final String VALUE_ELEMENT = "value";public static final String NULL_ELEMENT = "null";public static final String ARRAY_ELEMENT = "array";public static final String LIST_ELEMENT = "list";public static final String SET_ELEMENT = "set";public static final String MAP_ELEMENT = "map";public static final String ENTRY_ELEMENT = "entry";public static final String KEY_ELEMENT = "key";public static final String KEY_ATTRIBUTE = "key";public static final String KEY_REF_ATTRIBUTE = "key-ref";public static final String VALUE_REF_ATTRIBUTE = "value-ref";public static final String PROPS_ELEMENT = "props";public static final String PROP_ELEMENT = "prop";public static final String MERGE_ATTRIBUTE = "merge";public static final String QUALIFIER_ELEMENT = "qualifier";public static final String QUALIFIER_ATTRIBUTE_ELEMENT = "attribute";public static final String DEFAULT_LAZY_INIT_ATTRIBUTE = "default-lazy-init";public static final String DEFAULT_MERGE_ATTRIBUTE = "default-merge";public static final String DEFAULT_AUTOWIRE_ATTRIBUTE = "default-autowire";public static final String DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE = "default-dependency-check";public static final String DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE = "default-autowire-candidates";public static final String DEFAULT_INIT_METHOD_ATTRIBUTE = "default-init-method";public static final String DEFAULT_DESTROY_METHOD_ATTRIBUTE = "default-destroy-method";

接下来我们看一下对一个简单的bean注入的配置的解析处理操作。

<bean id="transaction" name="transaction" class="com.xxxx.aop.two.Transaction"></bean>

这里需要解析的元素有id，name和class三个标签，在上面均有定义。

在parseBeanDefinitionElement中会完成id和name标签的解析处理操作，并最终生成BeanDefinitionHolder返回，class标签的元素解析在parseBeanDefinitionElement中处理

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {//解析idString id = ele.getAttribute(ID_ATTRIBUTE);//解析nameString nameAttr = ele.getAttribute(NAME_ATTRIBUTE);//获取别名List<String> aliases = new ArrayList<String>();if (StringUtils.hasLength(nameAttr)) {String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);aliases.addAll(Arrays.asList(nameArr));}String beanName = id;if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {beanName = aliases.remove(0);if (logger.isDebugEnabled()) {logger.debug("No XML 'id' specified - using '" + beanName +"' as bean name and " + aliases + " as aliases");}}if (containingBean == null) {checkNameUniqueness(beanName, aliases, ele);}//解析其他元素标签AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);if (beanDefinition != null) {if (!StringUtils.hasText(beanName)) {try {if (containingBean != null) {beanName = BeanDefinitionReaderUtils.generateBeanName(beanDefinition, this.readerContext.getRegistry(), true);}else {beanName = this.readerContext.generateBeanName(beanDefinition);// Register an alias for the plain bean class name, if still possible,// if the generator returned the class name plus a suffix.// This is expected for Spring 1.2/2.0 backwards compatibility.String beanClassName = beanDefinition.getBeanClassName();if (beanClassName != null &&beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {aliases.add(beanClassName);}}if (logger.isDebugEnabled()) {logger.debug("Neither XML 'id' nor 'name' specified - " +"using generated bean name [" + beanName + "]");}}catch (Exception ex) {error(ex.getMessage(), ele);return null;}}String[] aliasesArray = StringUtils.toStringArray(aliases);//最终生成BeanDefinitionHolderreturn new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);}return null;}

接下来我们看看对class标签的解析处理操作。parseBeanDefinitionElement中会完成对class等其他标签的解析处理操作，最终生成BeanDefinition返回。

public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {this.parseState.push(new BeanEntry(beanName));//解析class标签内容String className = null;if (ele.hasAttribute(CLASS_ATTRIBUTE)) {className = ele.getAttribute(CLASS_ATTRIBUTE).trim();}try {String parent = null;if (ele.hasAttribute(PARENT_ATTRIBUTE)) {parent = ele.getAttribute(PARENT_ATTRIBUTE);}AbstractBeanDefinition bd = createBeanDefinition(className, parent);parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));parseMetaElements(ele, bd);parseLookupOverrideSubElements(ele, bd.getMethodOverrides());parseReplacedMethodSubElements(ele, bd.getMethodOverrides());parseConstructorArgElements(ele, bd);parsePropertyElements(ele, bd);parseQualifierElements(ele, bd);bd.setResource(this.readerContext.getResource());bd.setSource(extractSource(ele));//最终生成BeanDefinition返回return bd;}catch (ClassNotFoundException ex) {error("Bean class [" + className + "] not found", ele, ex);}catch (NoClassDefFoundError err) {error("Class that bean class [" + className + "] depends on not found", ele, err);}catch (Throwable ex) {error("Unexpected failure during bean definition parsing", ele, ex);}finally {this.parseState.pop();}return null;}

总结：绕了那么一大圈，Spring配置文件的解析处理操作是在BeanDefinitionParserDelegate中完成，当然也是只是完成了对Beans这个命名空间中的元素的解析处理操作，对于其他的命名空间是通过其他解析器进行解析操作的，接下来我们会进行分析，BeanDefinitionParserDelegate做的处理操作就是将bean的各种标签解析成BeanDefinition对象，并组装成BeanDefinitionHolder返回。