Spring源码分析之配置文件解析(二)

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找到了资源文件,接下来就是解析资源文件了,具体的解析工作是从XmlBeanDefinitionReader类的loadBeanDefinitions(Resource resource)方法开始。

一. loadBeanDefinitions(Resource resource)源码如下 XmlBeanDefinitionReader类

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

EncodedResource是对Resource的封装,采用装饰模式,主要是增加了编码的信息.

/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
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());
}

Set currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
“Detected cyclic loading of ” + encodedResource + ” – check your import definitions!”);
}
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
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();
}
}
}

这个方法里最核心的操作是doLoadBeanDefinitions(inputSource, encodedResource.getResource())
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
int validationMode = getValidationModeForResource(resource);
Document doc = this.documentLoader.loadDocument(
inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
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);
}
}

DocumentLoader类主要负责把一个XML文档解析成一个Document对象,注册beanDefinitions的工作交给registerBeanDefinitions方法了.

/**
* Register the bean definitions contained in the given DOM document.
* Called by loadBeanDefinitions.
*

Creates a new instance of the parser class and invokes
* registerBeanDefinitions on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// Read document based on new BeanDefinitionDocumentReader SPI.
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() – countBefore;
}

实际上XmlBeanDefinitionReader把解析注册的工作又转交给BeanDefinitionDocumentReader来完成了。

这里getRegistry()实际上返回的是上一节介绍的生成的DefaultListableBeanFactory,这个工厂实际上是在生成XmlBeanDefinitionReader对象时通过构造方法入参传入的。

这里的createReaderContext(Resource resource)应该特别注意一下,这个上下文中包含了很多重要的信息,以提供给BeanDefinitionDocumentReader来使用。

/**
* Create the {@link XmlReaderContext} to pass over to the document reader.
*/
protected XmlReaderContext createReaderContext(Resource resource) {
if (this.namespaceHandlerResolver == null) {
this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
}
return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
this.sourceExtractor, this, this.namespaceHandlerResolver);
}

二:我们来看看DefaultBeanDefinitionDocumentReader是如何来registerBeanDefinitions的.

/**
* Parses bean definitions according to the “spring-beans” DTD.
*

Opens a DOM Document; then initializes the default settings
* specified at level; then parses
* the contained bean definitions.
*/
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;

logger.debug(“Loading bean definitions”);
Element root = doc.getDocumentElement();

BeanDefinitionParserDelegate delegate = createHelper(readerContext, root);

preProcessXml(root);
parseBeanDefinitions(root, delegate);
postProcessXml(root);
}

我们继续来看一下核心操作parseDefaultElement(ele,delegate)方法。
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
}
Xml配置文件中的bean的解析注册就在processBeanDefinition中了。
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(“Failed to register bean definition with name ‘” +
bdHolder.getBeanName() + “‘”, ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
Spring把每一个Bean结点解析之后,生成底层的数据结构BeanDefinition,然后存储在BeanDefinitionHold中,很明显具体的真正的解析工作放在parseBeanDefinitionElement方法中,解析完成后则调用BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry())把beanDefinition注册到beanFactory中。下面,我们来看一下核心方法parseBeanDefinitionElement的源码.
三:我们来看看BeanDefinitionParserDelegate的parseBeanDefinitionElement(Element ele)是如何来解析的.
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return parseBeanDefinitionElement(ele, null);
}

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

List aliases = new ArrayList();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_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);
}

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);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}

return null;
}
在这里我们看到对id,name等属性的解析,最核心的操作为 AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {

this.parseState.push(new BeanEntry(beanName));

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));

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;
}
在这段代码中,你可清楚的看到对bean组件相关属性和子标记的解析和处理(根据方法的命名).
四:在这里,可以重点关注一下ParseState
public final class ParseState {

/**
* Tab character used when rendering the tree-style representation.
*/
private static final char TAB = ‘\t’;

/**
* Internal {@link Stack} storage.
*/
private final Stack state;

/**
* Create a new ParseState with an empty {@link Stack}.
*/
public ParseState() {
this.state = new Stack();
}

/**
* Create a new ParseState whose {@link Stack} is a {@link Object#clone clone}
* of that of the passed in ParseState.
*/
private ParseState(ParseState other) {
this.state = (Stack) other.state.clone();
}

/**
* Add a new {@link Entry} to the {@link Stack}.
*/
public void push(Entry entry) {
this.state.push(entry);
}

/**
* Remove an {@link Entry} from the {@link Stack}.
*/
public void pop() {
this.state.pop();
}

/**
* Return the {@link Entry} currently at the top of the {@link Stack} or
* null if the {@link Stack} is empty.
*/
public Entry peek() {
return (Entry) (this.state.empty() ? null : this.state.peek());
}

/**
* Create a new instance of {@link ParseState} which is an independent snapshot
* of this instance.
*/
public ParseState snapshot() {
return new ParseState(this);
}

/**
* Returns a tree-style representation of the current ParseState.
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
for (int x = 0; x < this.state.size(); x++) {
if (x > 0) {
sb.append(‘\n’);
for (int y = 0; y < x; y++) {
sb.append(TAB);
}
sb.append(“-> “);
}
sb.append(this.state.get(x));
}
return sb.toString();
}

/**
* Marker interface for entries into the {@link ParseState}.
*/
public interface Entry {

}

}
这个类用了比较巧妙的方式来跟踪解析过程中的相关步骤,用户详见源码和API。
Simple Stack-based structure for tracking the logical position during a parsing process. entries are added to the stack at each point during the parse phase in a reader-specific manner.
Calling toString() will render a tree-style view of the current logical position in the parse phase. This representation is intended for use in error messages.


来源:http://ddrv.cn

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