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(
我们知道在 Spring 中使用 DelegatingEntityResolver 为 EntityResolver 的实现类，resolveEntity() 实现如下：
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws SAXException, IOException { if (systemId != null) { if (systemId.endsWith(DTD_SUFFIX)) { return this.dtdResolver.resolveEntity(publicId, systemId); } else if (systemId.endsWith(XSD_SUFFIX)) { return this.schemaResolver.resolveEntity(publicId, systemId); } } return null; }不同的验证模式使用不同的解析器解析，如果是 DTD 验证模式则使用 BeansDtdResolver 来进行解析，如果是 XSD 则使用 PluggableSchemaResolver 来进行解析。
BeansDtdResolver 的解析过程如下:
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 && systemId.endsWith(DTD_EXTENSION)) { int lastPathSeparator = systemId.lastIndexOf('/'); int dtdNameStart = systemId.indexOf(DTD_NAME, lastPathSeparator); if (dtdNameStart != -1) { String dtdFile = DTD_NAME + DTD_EXTENSION; if (logger.isTraceEnabled()) { logger.trace("Trying to locate [" + dtdFile + "] in Spring jar on classpath"); } try { Resource resource = new ClassPathResource(dtdFile, getClass()); InputSource source = new InputSource(resource.getInputStream()); source.setPublicId(publicId); source.setSystemId(systemId); if (logger.isDebugEnabled()) { logger.debug("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); } } } } 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()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 并设置 publicId、systemId，然后返回。
PluggableSchemaResolver 的解析过程如下:
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) { String resourceLocation = getSchemaMappings().get(systemId); if (resourceLocation != null) { Resource resource = new ClassPathResource(resourceLocation, this.classLoader); try { InputSource source = new InputSource(r
