Spring源码-解析xml文件自定义标签
一、NamespaceHandlerResolver的创建
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 对xml的beanDefinition进行解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
// 完成具体的解析过程
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
public XmlReaderContext createReaderContext(Resource resource) {
return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
this.sourceExtractor, this, getNamespaceHandlerResolver());
}
public NamespaceHandlerResolver getNamespaceHandlerResolver() {
if (this.namespaceHandlerResolver == null) {
this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
}
return this.namespaceHandlerResolver;
}
protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
ClassLoader cl = (getResourceLoader() != null ? getResourceLoader().getClassLoader() : getBeanClassLoader());
return new DefaultNamespaceHandlerResolver(cl);
}
public DefaultNamespaceHandlerResolver(@Nullable ClassLoader classLoader) {
this(classLoader, DEFAULT_HANDLER_MAPPINGS_LOCATION); // public static final String DEFAULT_HANDLER_MAPPINGS_LOCATION = "META-INF/spring.handlers";
}
二、解析自定义标签
@Nullable
public BeanDefinition parseCustomElement(Element ele) {
return parseCustomElement(ele, null);
}
@Nullable
public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
// 获取对应的命名空间
String namespaceUri = getNamespaceURI(ele);
if (namespaceUri == null) {
return null;
}
// 根据命名空间找到对应的NamespaceHandler
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
// 调用自定义的NamespaceHandler进行解析
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
@Override
@Nullable
public NamespaceHandler resolve(String namespaceUri) {
// 获取所有已经配置好的handler映射
Map<String, Object> handlerMappings = getHandlerMappings();
// 根据命名空间找到对应的信息
Object handlerOrClassName = handlerMappings.get(namespaceUri);
if (handlerOrClassName == null) {
return null;
}
else if (handlerOrClassName instanceof NamespaceHandler) {
// 如果已经做过解析，直接从缓存中读取
return (NamespaceHandler) handlerOrClassName;
}
else {
// 没有做过解析，则返回的是类路径
String className = (String) handlerOrClassName;
try {
// 通过反射将类路径转化为类
Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
}
// 实例化类
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
// 调用自定义的namespaceHandler的初始化方法
/**
*以ContextNamespaceHandler为例
public class ContextNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
}
}
*/
namespaceHandler.init();
// 讲结果记录在缓存中
handlerMappings.put(namespaceUri, namespaceHandler);
return namespaceHandler;
}
catch (ClassNotFoundException ex) {
throw new FatalBeanException("Could not find NamespaceHandler class [" + className +
"] for namespace [" + namespaceUri + "]", ex);
}
catch (LinkageError err) {
throw new FatalBeanException("Unresolvable class definition for NamespaceHandler class [" +
className + "] for namespace [" + namespaceUri + "]", err);
}
}
}
/**
*从META-INF/Spring.handlers下加载配置到handlerMappings
*/
private Map<String, Object> getHandlerMappings() {
Map<String, Object> handlerMappings = this.handlerMappings;
// 如果没有被缓存，则开始进行缓存
if (handlerMappings == null) {
synchronized (this) {
handlerMappings = this.handlerMappings;
if (handlerMappings == null) {
if (logger.isTraceEnabled()) {
logger.trace("Loading NamespaceHandler mappings from [" + this.handlerMappingsLocation + "]");
}
try {
// this.handlerMappingsLocation在构造函数中已经被初始化为META-INF/Spring.handlers
Properties mappings =
PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
if (logger.isTraceEnabled()) {
logger.trace("Loaded NamespaceHandler mappings: " + mappings);
}
handlerMappings = new ConcurrentHashMap<>(mappings.size());
// 将properties格式文件合并到map格式的handlerMapping中
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
this.handlerMappings = handlerMappings;
}
catch (IOException ex) {
throw new IllegalStateException(
"Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
}
}
}
}
return handlerMappings;
}
以spring-context模块下的spring.handlers文件为例：
http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
http\://www.springframework.org/schema/jee=org.springframework.ejb.config.JeeNamespaceHandler
http\://www.springframework.org/schema/lang=org.springframework.scripting.config.LangNamespaceHandler
http\://www.springframework.org/schema/task=org.springframework.scheduling.config.TaskNamespaceHandler
http\://www.springframework.org/schema/cache=org.springframework.cache.config.CacheNamespaceHandler
调用自定义的NamespaceHandler进行解析
@Override
@Nullable
public BeanDefinition parse(Element element, ParserContext parserContext) {
// 获取元素的解析器
BeanDefinitionParser parser = findParserForElement(element, parserContext);
return (parser != null ? parser.parse(element, parserContext) : null);
}
@Nullable
private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
// 获取元素名称
String localName = parserContext.getDelegate().getLocalName(element);
// 根据元素名称找到对应的解析器
BeanDefinitionParser parser = this.parsers.get(localName);
if (parser == null) {
parserContext.getReaderContext().fatal(
"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
}
return parser;
}
下面以context下的property-placeholder为例，property-placeholder对应的BeanDefinitionParser为PropertyPlaceholderBeanDefinitionParser：
类AbstractBeanDefinitionParser:
@Override
@Nullable
public final BeanDefinition parse(Element element, ParserContext parserContext) {
AbstractBeanDefinition definition = parseInternal(element, parserContext);
if (definition != null && !parserContext.isNested()) {
try {
String id = resolveId(element, definition, parserContext); // 解析id属性
if (!StringUtils.hasText(id)) {
parserContext.getReaderContext().error(
"Id is required for element '" + parserContext.getDelegate().getLocalName(element)
+ "' when used as a top-level tag", element);
}
String[] aliases = null;
if (shouldParseNameAsAliases()) {
String name = element.getAttribute(NAME_ATTRIBUTE); // 解析name属性
if (StringUtils.hasLength(name)) {
aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
}
}
// 将AbstractBeanDefinition转换为BeanDefinitionHolder并注册
BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
registerBeanDefinition(holder, parserContext.getRegistry());
if (shouldFireEvents()) {
// 通知监听器进行处理
BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
postProcessComponentDefinition(componentDefinition);
parserContext.registerComponent(componentDefinition);
}
}
catch (BeanDefinitionStoreException ex) {
String msg = ex.getMessage();
parserContext.getReaderContext().error((msg != null ? msg : ex.toString()), element);
return null;
}
}
return definition;
}
将element和parserContext解析成BeanDefinition，解析id和name属性并注册到beanFactory。
类AbstractSingleBeanDefinitionParser：
@Override
protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
String parentName = getParentName(element);
if (parentName != null) {
builder.getRawBeanDefinition().setParentName(parentName);
}
// 获取自定义标签中的class，此时会调用自定义解析器
Class<?> beanClass = getBeanClass(element);
if (beanClass != null) {
builder.getRawBeanDefinition().setBeanClass(beanClass);
}
else {
// 若子类没有重写getBeanClass方法则尝试检查子类是否重写getBeanClassName方法
String beanClassName = getBeanClassName(element);
if (beanClassName != null) {
builder.getRawBeanDefinition().setBeanClassName(beanClassName);
}
}
builder.getRawBeanDefinition().setSource(parserContext.extractSource(element));
BeanDefinition containingBd = parserContext.getContainingBeanDefinition();
if (containingBd != null) {
// Inner bean definition must receive same scope as containing bean.
// 若存在父类则使用父类的scope属性
builder.setScope(containingBd.getScope());
}
if (parserContext.isDefaultLazyInit()) {
// Default-lazy-init applies to custom bean definitions as well.
// 配置延迟加载
builder.setLazyInit(true);
}
// 调用子类重写的doParse方法进行解析
doParse(element, parserContext, builder);
return builder.getBeanDefinition();
}
将element和parserContext解析成BeanDefinition，并可能设置parentName，beanClassName ，beanClass ，Scope，LazyInit等属性，调用doParse方法。BeanDefinition通过子类的getBeanClass或者getBeanClassName设置。
类AbstractPropertyLoadingBeanDefinitionParser：
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
String location = element.getAttribute("location");
if (StringUtils.hasLength(location)) {
location = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(location);
String[] locations = StringUtils.commaDelimitedListToStringArray(location);
builder.addPropertyValue("locations", locations);
}
String propertiesRef = element.getAttribute("properties-ref");
if (StringUtils.hasLength(propertiesRef)) {
builder.addPropertyReference("properties", propertiesRef);
}
String fileEncoding = element.getAttribute("file-encoding");
if (StringUtils.hasLength(fileEncoding)) {
builder.addPropertyValue("fileEncoding", fileEncoding);
}
String order = element.getAttribute("order");
if (StringUtils.hasLength(order)) {
builder.addPropertyValue("order", Integer.valueOf(order));
}
builder.addPropertyValue("ignoreResourceNotFound",
Boolean.valueOf(element.getAttribute("ignore-resource-not-found")));
builder.addPropertyValue("localOverride",
Boolean.valueOf(element.getAttribute("local-override")));
builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
}
解析相应属性并设置到BeanDefinitionBuilder中
类PropertyPlaceholderBeanDefinitionParser：
protected Class<?> getBeanClass(Element element) {
// As of Spring 3.1, the default value of system-properties-mode has changed from
// 'FALLBACK' to 'ENVIRONMENT'. This latter value indicates that resolution of
// placeholders against system properties is a function of the Environment and
// its current set of PropertySources.
if (SYSTEM_PROPERTIES_MODE_DEFAULT.equals(element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE))) {
return PropertySourcesPlaceholderConfigurer.class;
}
// The user has explicitly specified a value for system-properties-mode: revert to
// PropertyPlaceholderConfigurer to ensure backward compatibility with 3.0 and earlier.
// This is deprecated; to be removed along with PropertyPlaceholderConfigurer itself.
return org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.class;
}
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
super.doParse(element, parserContext, builder); // 调用父类方法解析相应属性
builder.addPropertyValue("ignoreUnresolvablePlaceholders",
Boolean.valueOf(element.getAttribute("ignore-unresolvable")));
String systemPropertiesModeName = element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE);
if (StringUtils.hasLength(systemPropertiesModeName) &&
!systemPropertiesModeName.equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
builder.addPropertyValue("systemPropertiesModeName", "SYSTEM_PROPERTIES_MODE_" + systemPropertiesModeName);
}
if (element.hasAttribute("value-separator")) {
builder.addPropertyValue("valueSeparator", element.getAttribute("value-separator"));
}
if (element.hasAttribute("trim-values")) {
builder.addPropertyValue("trimValues", element.getAttribute("trim-values"));
}
if (element.hasAttribute("null-value")) {
builder.addPropertyValue("nullValue", element.getAttribute("null-value"));
}
}
解析属性
