标签:publicId String Spring InputSource systemId EntityResolver logger Document IoC
目录前言
在 XmlBeanDefinitionReader#document(InputSource inputSource,Resource resource)
方法中,主要做了两件事:
- 调用
\#getValidationModeForResource(Resource resource)
获取指定资源xml的验证模式。上篇博文中已经做了详细的解析。 - 调用
DocumentLoader#loadDocument(InputSource inputSource, EntityResolver entityResolver, ErrorHandler errorHandler, int validationMode, boolean namespaceAware)
方法,获取 XML Document 实例。
1 DocumentLoader
获取 Document 的策略,有接口,org.springframework.beans.factory.xml.DocumentLoader
定义。代码如下:
定义从资源文件加载到转换为 Document 的功能。
public interface DocumentLoader {
Document loadDocument(
InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware)
throws Exception;
}
inputSource
方法参数,加载 Document 的 Resource 资源。entityResolver
方法参数,解析文件的解析器。errorHandler
方法参数,处理加载 Document 对象的过程的错误。validationMode
方法参数,验证模式。namespaceAware
方法参数,命名空间支持。如果要提供对 XML 名称空间的支持,则需要值为true
。
1.1 DefauleDocumentLoader
该方法有DocumentLoader 的默认实现类,org.springframework.beans.factory.xml.DefaultDocumentLoader
实现。代码如下:
/**
* Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
* XML parser.
*/
@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver, ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
// <1> 创建 DocumentBuilderFactory
DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isTraceEnabled()) {
logger.trace("Using JAXP provider [" + factory.getClass().getName() + "]");
}
// <2> 创建 DocumentBuilder
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
// <3> 解析 XML InputSource 返回 Document 对象
return builder.parse(inputSource);
}
- 首先,调用
#createDocumentBuilderFactory(...)
方法,创建javax.xml.parsers.DocumentBuilderFactory
对象。代码如下:
/**
* JAXP attribute used to configure the schema language for validation.
*/
private static final String SCHEMA_LANGUAGE_ATTRIBUTE = "http://java.sun.com/xml/jaxp/properties/schemaLanguage";
/**
* JAXP attribute value indicating the XSD schema language.
*/
private static final String XSD_SCHEMA_LANGUAGE = "http://www.w3.org/2001/XMLSchema";
protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware) throws ParserConfigurationException {
// 创建 DocumentBuilderFactory
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(namespaceAware); // 设置命名空间支持
if (validationMode != XmlValidationModeDetector.VALIDATION_NONE) {
factory.setValidating(true); // 开启校验
// XSD 模式下,设置 factory 的属性
if (validationMode == XmlValidationModeDetector.VALIDATION_XSD) {
// Enforce namespace aware for XSD...
factory.setNamespaceAware(true); // XSD 模式下,强制设置命名空间支持
// 设置 SCHEMA_LANGUAGE_ATTRIBUTE
try {
factory.setAttribute(SCHEMA_LANGUAGE_ATTRIBUTE, XSD_SCHEMA_LANGUAGE);
} catch (IllegalArgumentException ex) {
ParserConfigurationException pcex = new ParserConfigurationException(
"Unable to validate using XSD: Your JAXP provider [" + factory +
"] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? " +
"Upgrade to Apache Xerces (or Java 1.5) for full XSD support.");
pcex.initCause(ex);
throw pcex;
}
}
}
return factory;
}
- 然后,调用
#createDocumentBuilder(DocumentBuilderFactory factory, EntityResolver entityResolver,ErrorHandler errorHandler)
方法,创建javax.xml.parsers.DocumentBuilder
对象。代码如下:
protected DocumentBuilder createDocumentBuilder(DocumentBuilderFactory factory,
@Nullable EntityResolver entityResolver, @Nullable ErrorHandler errorHandler)
throws ParserConfigurationException {
// 创建 DocumentBuilder 对象
DocumentBuilder docBuilder = factory.newDocumentBuilder();
// <x> 设置 EntityResolver 属性
if (entityResolver != null) {
docBuilder.setEntityResolver(entityResolver);
}
// 设置 ErrorHandler 属性
if (errorHandler != null) {
docBuilder.setErrorHandler(errorHandler);
}
return docBuilder;
}
在
- 最后,调用
DocumentBuilder#parse(InputSource)
方法,解析 InputSource ,返回 Document 对象
2 EntityResolver
通过 DocumentLoader#loadDocument(...)
方法来获取Document 对象,有一个方法参数entityResolver。该参数是通过,XmlBeanDefinitionReader#getEntityResolver()
方法来获取的。代码如下:
#getEntityResolver()
方法,返回指定的解析器,如果没有指定,则构造一个未指定的默认解析器。
// XmlBeanDefinitionReader.java
/**
* EntityResolver 解析器
*/
@Nullable
private EntityResolver entityResolver;
protected EntityResolver getEntityResolver() {
if (this.entityResolver == null) {
// Determine default EntityResolver to use.
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader != null) {
this.entityResolver = new ResourceEntityResolver(resourceLoader);
} else {
this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());
}
}
return this.entityResolver;
}
- 如果ResourceLoader 不为null , 则根据指定的ResourceLoader 创建一个ResourceEntityResolver 对象。
- 如果ResourceLoader 为null,则创建一个 DelegatingEntityResolver 对象,该 Resolver 委托给默认的 BeansDtdResolver 和 PluggableSchemaResolver 。
2.1 子类
上面的方法,一共涉及四个EntityResolver 的子类:
org.springframework.beans.factory.xm.beansDtdResolver
: 实现EntityResolver接口,Spring Bean dtd 解码器,用来从classpath
或者 jar 文件中加载 dtd 。部分代码如下:
private static final String DTD_EXTENSION = ".dtd";
private static final String DTD_NAME = "spring-beans";
org.springframework.beans.factory.xml.PluggableSchemaResolver
,实现 EntityResolver 接口,读取 classpath 下的所有"META-INF/spring.schemas"
成一个 namespaceURI 与 Schema 文件地址的 map 。代码如下:
/**
* The location of the file that defines schema mappings.
* Can be present in multiple JAR files.
*
* 默认 {@link #schemaMappingsLocation} 地址
*/
public static final String DEFAULT_SCHEMA_MAPPINGS_LOCATION = "META-INF/spring.schemas";
@Nullable
private final ClassLoader classLoader;
/**
* Schema 文件地址
*/
private final String schemaMappingsLocation;
/** Stores the mapping of schema URL -> local schema path. */
@Nullable
private volatile Map<String, String> schemaMappings; // namespaceURI 与 Schema 文件地址的映射集合
org.springframework.beans.factory.xml.DelegatingEntityResolver
:实现 EntityResolver 接口,分别代理 dtd 的 BeansDtdResolver 和 xml schemas 的 PluggableSchemaResolver 。代码如下:
/** Suffix for DTD files. */
public static final String DTD_SUFFIX = ".dtd";
/** Suffix for schema definition files. */
public static final String XSD_SUFFIX = ".xsd";
private final EntityResolver dtdResolver;
private final EntityResolver schemaResolver;
// 默认
public DelegatingEntityResolver(@Nullable ClassLoader classLoader) {
this.dtdResolver = new BeansDtdResolver();
this.schemaResolver = new PluggableSchemaResolver(classLoader);
}
// 自定义
public DelegatingEntityResolver(EntityResolver dtdResolver, EntityResolver schemaResolver) {
Assert.notNull(dtdResolver, "'dtdResolver' is required");
Assert.notNull(schemaResolver, "'schemaResolver' is required");
this.dtdResolver = dtdResolver;
this.schemaResolver = schemaResolver;
}
org.springframework.beans.factory.xml.ResourceEntityResolver
:继承自 DelegatingEntityResolver 类,通过 ResourceLoader 来解析实体的引用。代码如下:
private final ResourceLoader resourceLoader;
public ResourceEntityResolver(ResourceLoader resourceLoader) {
super(resourceLoader.getClassLoader());
this.resourceLoader = resourceLoader;
}
2.2 作用
EntityResolver 的作用就是,通过实现它,应用可以自定义如何寻找【验证文件】的逻辑。
org.xml.sax.EntityResolver
接口,代码如下:
public interface EntityResolver {
public abstract InputSource resolveEntity (String publicId, String systemId)
throws SAXException, IOException;
}
接口方法接收两个参数 publicId
和 systemId
,并返回 InputSource 对象。两个参数声明如下:
publicId
:被引用的外部实体的公共标识符,如果没有提供,则返回null
。systemId
:被引用的外部实体的系统标识符。
这两个参数的实际内容和具体的验证模式的关系如下:
-
XSD 验证模式
-
publicId:null
-
systemId:http://www.springframework.org/schema/beans/spring-beans.xsd
-
-
DTD 验证模式
-
publicId:-//SPRING//DTD BEAN 2.0//EN
-
systemId:http://www.springframework.org/dtd/spring-beans.dtd
-
2.3 DelegatingEntityResolver
我们知道在 Spring 中使用 DelegatingEntityResolver 为 EntityResolver 的实现类。#resolveEntity(String publicId, String systemId)
方法,实现如下:
@Override
@Nullable
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws SAXException, IOException {
if (systemId != null) {
// DTD 模式
if (systemId.endsWith(DTD_SUFFIX)) {
return this.dtdResolver.resolveEntity(publicId, systemId);
// XSD 模式
} else if (systemId.endsWith(XSD_SUFFIX)) {
return this.schemaResolver.resolveEntity(publicId, systemId);
}
}
return null;
}
- 如果是 DTD 验证模式,则使用 BeansDtdResolver 来进行解析
- 如果是 XSD 验证模式,则使用 PluggableSchemaResolver 来进行解析。
2.4 BeansDtdResolver
BeansDtdResolver 的解析过程,代码如下:
/**
* DTD 文件的后缀
*/
private static final String DTD_EXTENSION = ".dtd";
/**
* Spring Bean DTD 的文件名
*/
private static final String DTD_NAME = "spring-beans";
@Override
@Nullable
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws IOException {
if (logger.isTraceEnabled()) {
logger.trace("Trying to resolve XML entity with public ID [" + publicId +
"] and system ID [" + systemId + "]");
}
// 必须以 .dtd 结尾
if (systemId != null && systemId.endsWith(DTD_EXTENSION)) {
// 获取最后一个 / 的位置
int lastPathSeparator = systemId.lastIndexOf('/');
// 获取 spring-beans 的位置
int dtdNameStart = systemId.indexOf(DTD_NAME, lastPathSeparator);
if (dtdNameStart != -1) { // 找到
String dtdFile = DTD_NAME + DTD_EXTENSION;
if (logger.isTraceEnabled()) {
logger.trace("Trying to locate [" + dtdFile + "] in Spring jar on classpath");
}
try {
// 创建 ClassPathResource 对象
Resource resource = new ClassPathResource(dtdFile, getClass());
// 创建 InputSource 对象,并设置 publicId、systemId 属性
InputSource source = new InputSource(resource.getInputStream());
source.setPublicId(publicId);
source.setSystemId(systemId);
if (logger.isTraceEnabled()) {
logger.trace("Found beans DTD [" + systemId + "] in classpath: " + dtdFile);
}
return source;
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve beans DTD [" + systemId + "]: not found in classpath", ex);
}
}
}
}
// 使用默认行为,从网络上下载
// Use the default behavior -> download from website or wherever.
return null;
}
从上面的代码中,我们可以看到,加载 DTD 类型的 BeansDtdResolver#resolveEntity(...)
过程,只是对 systemId
进行了简单的校验(从最后一个 / 开始,内容中是否包含 spring-beans
),然后构造一个 InputSource 对象,并设置 publicId
、systemId
属性,然后返回。
2.5 PluggableSchemaResolver
PluggableSchemaResolver 的解析过程,代码如下:
@Nullable
private final ClassLoader classLoader;
/**
* Schema 文件地址
*/
private final String schemaMappingsLocation;
/** Stores the mapping of schema URL -> local schema path. */
@Nullable
private volatile Map<String, String> schemaMappings; // namespaceURI 与 Schema 文件地址的映射集合
@Override
@Nullable
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws IOException {
if (logger.isTraceEnabled()) {
logger.trace("Trying to resolve XML entity with public id [" + publicId +
"] and system id [" + systemId + "]");
}
if (systemId != null) {
// 获得 Resource 所在位置
String resourceLocation = getSchemaMappings().get(systemId);
if (resourceLocation != null) {
// 创建 ClassPathResource
Resource resource = new ClassPathResource(resourceLocation, this.classLoader);
try {
// 创建 InputSource 对象,并设置 publicId、systemId 属性
InputSource source = new InputSource(resource.getInputStream());
source.setPublicId(publicId);
source.setSystemId(systemId);
if (logger.isTraceEnabled()) {
logger.trace("Found XML schema [" + systemId + "] in classpath: " + resourceLocation);
}
return source;
}
catch (FileNotFoundException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not find XML schema [" + systemId + "]: " + resource, ex);
}
}
}
}
return null;
}
-
首先调用
#getSchemaMappings()
方法,获取一个映射表(systemId 与其在本地的对照关系)。代码如下:private Map<String, String> getSchemaMappings() { Map<String, String> schemaMappings = this.schemaMappings; // 双重检查锁,实现 schemaMappings 单例 if (schemaMappings == null) { synchronized (this) { schemaMappings = this.schemaMappings; if (schemaMappings == null) { if (logger.isTraceEnabled()) { logger.trace("Loading schema mappings from [" + this.schemaMappingsLocation + "]"); } try { // 以 Properties 的方式,读取 schemaMappingsLocation Properties mappings = PropertiesLoaderUtils.loadAllProperties(this.schemaMappingsLocation, this.classLoader); if (logger.isTraceEnabled()) { logger.trace("Loaded schema mappings: " + mappings); } // 将 mappings 初始化到 schemaMappings 中 schemaMappings = new ConcurrentHashMap<>(mappings.size()); CollectionUtils.mergePropertiesIntoMap(mappings, schemaMappings); this.schemaMappings = schemaMappings; } catch (IOException ex) { throw new IllegalStateException( "Unable to load schema mappings from location [" + this.schemaMappingsLocation + "]", ex); } } } } return schemaMappings; }
-
然后,根据传入的
systemId
获取该systemId
在本地的路径resourceLocation
。 -
最后,根据
resourceLocation
,构造 InputSource 对象。
2.6 ResourceEntityResolver
ResourceEntityResolver 的解析过程,代码如下:
private final ResourceLoader resourceLoader;
@Override
@Nullable
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws SAXException, IOException {
// 调用父类的方法,进行解析
InputSource source = super.resolveEntity(publicId, systemId);
// 解析失败,resourceLoader 进行解析
if (source == null && systemId != null) {
// 获得 resourcePath ,即 Resource 资源地址
String resourcePath = null;
try {
String decodedSystemId = URLDecoder.decode(systemId, "UTF-8"); // 使用 UTF-8 ,解码 systemId
String givenUrl = new URL(decodedSystemId).toString(); // 转换成 URL 字符串
// 解析文件资源的相对路径(相对于系统根路径)
String systemRootUrl = new File("").toURI().toURL().toString();
// Try relative to resource base if currently in system root.
if (givenUrl.startsWith(systemRootUrl)) {
resourcePath = givenUrl.substring(systemRootUrl.length());
}
} catch (Exception ex) {
// Typically a MalformedURLException or AccessControlException.
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve XML entity [" + systemId + "] against system root URL", ex);
}
// No URL (or no resolvable URL) -> try relative to resource base.
resourcePath = systemId;
}
if (resourcePath != null) {
if (logger.isTraceEnabled()) {
logger.trace("Trying to locate XML entity [" + systemId + "] as resource [" + resourcePath + "]");
}
// 获得 Resource 资源
Resource resource = this.resourceLoader.getResource(resourcePath);
// 创建 InputSource 对象
source = new InputSource(resource.getInputStream());
// 设置 publicId 和 systemId 属性
source.setPublicId(publicId);
source.setSystemId(systemId);
if (logger.isDebugEnabled()) {
logger.debug("Found XML entity [" + systemId + "]: " + resource);
}
}
}
return source;
}
- 首先,调用父类的方法,进行解析。
- 如果失败,使用
resourceLoader
,尝试读取systemId
对应的 Resource 资源。
2.7 自定义 EntityResolver
#getEntityResolver()
方法返回 EntityResolver 对象。那么怎么进行自定义 EntityResolver 呢?
If a SAX application needs to implement customized handling for external entities, it must implement this interface and register an instance with the SAX driver using the setEntityResolver method.
就是说:如果 SAX 应用程序需要实现自定义处理外部实体,则必须实现此接口,并使用
#setEntityResolver(EntityResolver entityResolver)
方法,向 SAX 驱动器注册一个 EntityResolver 实例。
示例如下:
public class MyResolver implements EntityResolver {
@Override
public InputSource resolveEntity(String publicId, String systemId) {
if (systemId.equals("http://www.myhost.com/today")) {
MyReader reader = new MyReader();
return new InputSource(reader);
} else {
// use the default behaviour
return null;
}
}
}
我们首先将 "spring-student.xml"
文件中的 XSD 声明的地址改掉,如下:
如果我们再次运行,则会报如下错误:
从上面的错误可以看到,是在进行文档验证时,无法根据声明找到 XSD 验证文件而导致无法进行 XML 文件验证。在 《【死磕 Spring】—— IoC 之获取验证模型》 中讲到,如果要解析一个 XML 文件,SAX 首先会读取该 XML 文档上的声明,然后根据声明去寻找相应的 DTD 定义,以便对文档进行验证。默认的加载规则是通过网络方式下载验证文件,而在实际生产环境中我们会遇到网络中断或者不可用状态,那么就应用就会因为无法下载验证文件而报错。
标签:publicId,String,Spring,InputSource,systemId,EntityResolver,logger,Document,IoC 来源: https://www.cnblogs.com/zhaoqiang-lab/p/16164218.html
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