基于schema的spring xml namespace扩展_schemamappings加载位置-优快云博客

基于schema的spring xml namespace扩展

Spring2.0后，可以基于spring的schema来扩展xml format,加入自定义的schema元素。

步骤如下:
1.定义xml schema描述个性化的元素信息
2.编写自定义的NamespaceHandler
3.编写一个或多个BeanDefinitionParser来解析Xml元素
4.注册成为spring的artifacts
demo可以参考http://static.springsource.org/spring/docs/2.5.x/reference/extensible-xml.html

说明：
spring.schema定义uri对应的xsd的位置，基于classpath
spring.handlers定义uri对应的解析类

spring.schema基本思路：
1.spring在解析XML配置文件时，通过DelegatingEntityResolver来解析xml中的元素信息，包括header信息.

初始化：

public DelegatingEntityResolver(ClassLoaderclassLoader) {

this.dtdResolver= new BeansDtdResolver();

this.schemaResolver= new PluggableSchemaResolver(classLoader);

}

调用PluggableSchemaResolver:

public InputSource resolveEntity(StringpublicId, String systemId) throws SAXException, IOException {

if(systemId != null) {

if(systemId.endsWith(DTD_SUFFIX)) {

returnthis.dtdResolver.resolveEntity(publicId, systemId);

}

elseif (systemId.endsWith(XSD_SUFFIX)) {

returnthis.schemaResolver.resolveEntity(publicId, systemId);

}

returnnull;

}

2.PluggableSchemaResolver来解析指定的资源

public static final StringDEFAULT_SCHEMA_MAPPINGS_LOCATION = "META-INF/spring.schemas";

调用工具类加载资源信息

private Map<String, String>getSchemaMappings() {

if(this.schemaMappings == null) {

synchronized(this) {

if(this.schemaMappings == null) {

if(logger.isDebugEnabled()) {

logger.debug("Loadingschema mappings from [" + this.schemaMappingsLocation + "]");

}

try{

Propertiesmappings =

PropertiesLoaderUtils.loadAllProperties(this.schemaMappingsLocation,this.classLoader);

if(logger.isDebugEnabled()) {

logger.debug("Loadedschema mappings: " + mappings);

}

Map<String,String> schemaMappings = new ConcurrentHashMap<String, String>();

CollectionUtils.mergePropertiesIntoMap(mappings,schemaMappings);

this.schemaMappings= schemaMappings;

}

catch(IOException ex) {

thrownew IllegalStateException(

"Unableto load schema mappings from location [" + this.schemaMappingsLocation +"]", ex);

}

returnthis.schemaMappings;

}

3.PropertiesLoaderUtils
根据classloader加载所有的资源，注意因为不同的jar包的资源名字可能相同，所以使用的是classloader的getResources接口：

public static PropertiesloadAllProperties(String resourceName, ClassLoader classLoader) throwsIOException {

Assert.notNull(resourceName,"Resource name must not be null");

ClassLoaderclToUse = classLoader;

if(clToUse == null) {

clToUse= ClassUtils.getDefaultClassLoader();

}

Propertiesproperties = new Properties();

Enumerationurls = clToUse.getResources(resourceName);

while(urls.hasMoreElements()) {

URLurl = (URL) urls.nextElement();

InputStreamis = null;

try{

URLConnectioncon = url.openConnection();

con.setUseCaches(false);

is= con.getInputStream();

properties.load(is);

}

finally{

if(is != null) {

is.close();

}

returnproperties;

}

4.根据xml中的自定义元素根据指定的xsd类型信息来验证。

public InputSource resolveEntity(StringpublicId, String systemId) throws IOException {

if(logger.isTraceEnabled()) {

logger.trace("Tryingto resolve XML entity with public id [" + publicId +

"]and system id [" + systemId + "]");

}

if(systemId != null) {

StringresourceLocation = getSchemaMappings().get(systemId);

if(resourceLocation != null) {

Resourceresource = new ClassPathResource(resourceLocation, this.classLoader);

try{

InputSourcesource = new InputSource(resource.getInputStream());

source.setPublicId(publicId);

source.setSystemId(systemId);

if(logger.isDebugEnabled()) {

logger.debug("FoundXML schema [" + systemId + "] in classpath: " +resourceLocation);

}

returnsource;

}

catch(FileNotFoundException ex) {

if(logger.isDebugEnabled()) {

logger.debug("Couldn'tfind XML schema [" + systemId + "]: " + resource, ex);

}

returnnull;

}

spring.handles基本思路：

1.spring 在解析xml元素后，要通过XmlBeanDefinitionReader转换成Bean Definition信息。

1.1将前面提到的DelegatingEntityResolver(PluggableSchemaResolver)放到DocumentLoader中
1.2注册bean definition到Dom中

viewplain

protected int doLoadBeanDefinitions(InputSourceinputSource, Resource resource)

throwsBeanDefinitionStoreException {

try {

intvalidationMode = getValidationModeForResource(resource);

Documentdoc = this.documentLoader.loadDocument(

inputSource,getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());

returnregisterBeanDefinitions(doc, resource);

}

catch(BeanDefinitionStoreException ex) {

throw ex;

}

catch(SAXParseException ex) {

throw newXmlBeanDefinitionStoreException(resource.getDescription(),

"Line" + ex.getLineNumber() + " in XML document from " + resource +" is invalid", ex);

}

catch(SAXException ex) {

throw newXmlBeanDefinitionStoreException(resource.getDescription(),

"XMLdocument from " + resource + " is invalid", ex);

}

catch(ParserConfigurationException ex) {

throw newBeanDefinitionStoreException(resource.getDescription(),

"Parserconfiguration exception parsing XML from " + resource, ex);

}

catch(IOException ex) {

throw newBeanDefinitionStoreException(resource.getDescription(),

"IOExceptionparsing XML document from " + resource, ex);

}

catch(Throwable ex) {

throw newBeanDefinitionStoreException(resource.getDescription(),

"Unexpectedexception parsing XML document from " + resource, ex);

}

2.调用DefaultDocumentLoader，将前面提到的DelegatingEntityResolver(PluggableSchemaResolver)放到DocumentLoader中

protected DocumentBuilder createDocumentBuilder(

DocumentBuilderFactoryfactory, EntityResolver entityResolver, ErrorHandler errorHandler)

throwsParserConfigurationException {

DocumentBuilderdocBuilder = factory.newDocumentBuilder();

if(entityResolver != null) {

docBuilder.setEntityResolver(entityResolver);

}

if(errorHandler != null) {

docBuilder.setErrorHandler(errorHandler);

}

returndocBuilder;

}

3. 注册beandefinition到Dom中,在遍历xml元素，如果是子定义的元素，调用spring.handlers定义的解析类来解析

public int registerBeanDefinitions(Document doc, Resourceresource) throws BeanDefinitionStoreException {

// Readdocument based on new BeanDefinitionDocumentReader SPI.

BeanDefinitionDocumentReaderdocumentReader = createBeanDefinitionDocumentReader();

intcountBefore = getRegistry().getBeanDefinitionCount();

documentReader.registerBeanDefinitions(doc,createReaderContext(resource));

returngetRegistry().getBeanDefinitionCount() - countBefore;

}

protectedXmlReaderContext createReaderContext(Resource resource) {

if(this.namespaceHandlerResolver == null) {

this.namespaceHandlerResolver= createDefaultNamespaceHandlerResolver();

}

return newXmlReaderContext(resource, this.problemReporter, this.eventListener,

this.sourceExtractor,this, this.namespaceHandlerResolver);

}

4.剩下就是ApplicationContext根据解析后的Bean Definition来构造Bean的实例了。