java - 解析时调用 SAX error() 处理程序方法，但没有抛出异常 - 为什么？

Question

我想在解析 XML 文件时对其进行验证。使用 Validator.validate() 进行独立验证表示没问题，解析时不会引发异常，但会调用解析处理程序中的[覆盖] error() 方法。为什么？我需要初始化一些状态吗？如果我故意使 XML 文件不正确，则独立验证将失败，如果我注释掉验证，解析也会失败 - 都会出现 SAXParseException 以及我预期的错误。

[下面的代码是根据实际内容进行编辑的，其中包含大量 println 以说明问题]

短.xsd:

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://www.myapp.com/sample"
           xmlns:smp="http://www.myapp.com/sample"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified">
  <xs:element name="Sample" type="xs:string"/>
</xs:schema>

short.xml:

<?xml version="1.0"?>
<Sample
  xmlns="http://www.myapp.com/sample"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.myapp.com/sample shortxsd.xsd"
>
  hello
</Sample>

来源:

import javax.xml.XMLConstants;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;

public static void main(String... args)
      throws IOException
  {
    String xsdFileName = "shortxsd.xsd";
    URL xsdURL = Thread.currentThread().getContextClassLoader().getResource(xsdFileName);
    String xsdPath = xsdURL.getPath();
    System.out.println("xsdFileName: " + xsdFileName);
    System.out.println("xsdURL: " + xsdURL);
    System.out.println("xsdPath: " + xsdPath);

    String xmlFileName = "shortxml.xml";
    URL xmlURL = Thread.currentThread().getContextClassLoader().getResource(xmlFileName);
    String xmlPath = xmlURL.getPath();
    System.out.println("xmlFileName: " + xmlFileName);
    System.out.println("xmlURL: " + xmlURL);
    System.out.println("xmlPath: " + xmlPath);

    /* Schema creation: */
    SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
    Schema schema = null;
    try {
      schema = schemaFactory.newSchema(new File(xsdURL.getFile()));
    }
    catch (SAXException ex) {
      System.out.println("Schema creation exception: " + ex);
      return;
    }
    System.out.println("+ Schema creation OK");

    /* Stand-alone Validation: */
    Validator validator = schema.newValidator();
    Source xmlFile = new StreamSource(xmlURL.openStream());
    try {
      validator.validate(xmlFile);
    }
    catch (SAXException ex) {
      System.out.println("Validation exception: " + ex);
      return;
    }
    System.out.println("+ Stand-alone Validation OK");

    /* Parsing with validation: */
    SAXParserFactory parserFactory = SAXParserFactory.newInstance();
    parserFactory.setSchema(schema);
    SAXParser saxParser = null;
    try {
      saxParser = parserFactory.newSAXParser();
    }
    catch (ParserConfigurationException |
           SAXException ex) {
      System.out.println("Parser creation exception: " + ex);
      return;
    }
    System.out.println("+ Parser creation OK");

    try (InputStream xmlInput = xmlURL.openStream()) {
      saxParser.parse(xmlInput, new DefaultHandler()
                  {
                    @Override
                    public void error(SAXParseException e)
                    {
                      System.out.println("# Error: " + e);
                    }
      });
    }
    catch (SAXException ex) {
      System.out.println("Parsing exception: " + ex);
      return;
    }
    System.out.println("+ Parsing OK");
  }

输出:

xsdFileName: shortxsd.xsd
xsdURL: file:/.../target/classes/shortxsd.xsd
xsdPath: /.../target/classes/shortxsd.xsd
xmlFileName: shortxml.xml
xmlURL: file:/.../target/classes/shortxml.xml
xmlPath: /.../target/classes/shortxml.xml
+ Schema creation OK
+ Stand-alone Validation OK
+ Parser creation OK
# Error: org.xml.sax.SAXParseException; lineNumber: 6; columnNumber: 2; cvc-elt.1: Cannot find the declaration of element 'Sample'.
+ Parsing OK

Answer 1

您需要将 SAX 解析器配置为具有 namespace 感知能力。

如果您从 XML 文档中删除 xmlns="..." 属性，以及 xmlns:smp="..." 和 targetNamespace ="..." 属性来自您的 XML 架构，您的代码不会产生任何错误消息。所以问题一定与命名空间有关。

要使 SAX 解析器能够感知命名空间，请在工厂中设置一个选项:

    /* Parsing with validation: */
    SAXParserFactory parserFactory = SAXParserFactory.newInstance();
    parserFactory.setNamespaceAware(true); // add this line
    parserFactory.setSchema(schema);

我对您的代码进行了此更改，最后打印出了四条 OK 消息。