在下面的代码示例中，我使用 STaX 解析器来解析一段 XML。如果我通过它运行 xml10，它会按预期工作。 xml11 字符串(相同，除了 xml 版本)- 它抛出 NullPointerException。我在使用 JDK 1.6 的 Mac 上运行它。

import javax.xml.namespace.QName;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.StringReader;
import java.util.Stack;

/**
 */
public class StaxSucks {

    static String xml10 ="<?xml version=\"1.0\" encoding=\"utf-8\" ?>\n"+
                        "<anElement/>";

    static String xml11 ="<?xml version=\"1.1\" encoding=\"utf-8\" ?>\n"+
            "<anElement/>";


    static void parse(InputStream is) throws Exception{
        final XMLInputFactory factory = XMLInputFactory.newInstance();
        factory.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES, Boolean.FALSE);
        final XMLStreamReader xmlStreamReader = factory.createXMLStreamReader(is);
        Stack<QName> XMLDEPTH = new Stack<QName>();
        int eventType = xmlStreamReader.next();
        while(eventType != XMLStreamConstants.END_DOCUMENT){
            if(XMLStreamConstants.START_ELEMENT == eventType){
                QName eventName = xmlStreamReader.getName();
                XMLDEPTH.push(eventName);
            }else if(XMLStreamConstants.END_ELEMENT == eventType){
                //ends should always match the starts.
                QName eventName = xmlStreamReader.getName();
                if(XMLDEPTH.peek().equals(eventName)){
                    XMLDEPTH.pop();
                }else{
                    System.out.println("Hit an end with a non-matching beginning:"+eventName);
                }
            } else{
                System.out.println("Hit event type:"+eventType);
            }
            eventType = xmlStreamReader.next();
        }
        System.out.println("Stack is empty:"+XMLDEPTH.empty());

    }

    public static void main(String[] args) throws Exception{
        System.out.println("Starting XML1.0");
        InputStream is = new ByteArrayInputStream(xml10.getBytes("utf8"));
        parse(is);
        System.out.println("Starting XML1.1");
        is = new ByteArrayInputStream(xml11.getBytes("utf8"));
        parse(is);
    }
}

堆栈跟踪:

Exception in thread "main" java.lang.NullPointerException
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.scanStartElement(XML11NSDocumentScannerImpl.java:351)
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl$NS11ContentDriver.scanRootElementHook(XML11NSDocumentScannerImpl.java:889)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3104)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:922)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.next(XML11NSDocumentScannerImpl.java:852)
    at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:554)
    at StaxSucks.parse(StaxSucks.java:46)
    at StaxSucks.main(StaxSucks.java:74)

最佳答案

您好，这是 Sun/Oracle JDK 中 stax 实现损坏的情况，IBM JDK 工作正常，或者您甚至可以只使用最新的 Xerces jar，就可以了。

您可以从以下位置下载 xerces jar: http://xerces.apache.org/mirrors.cgi#binary

dims@dims-laptop-520:~/test$ /usr/lib/jvm/java-6-sun/bin/java -cp . StaxSucks
Starting XML1.0
Stack is empty:true
Starting XML1.1
Exception in thread "main" java.lang.NullPointerException
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.scanStartElement(XML11NSDocumentScannerImpl.java:351)
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl$NS11ContentDriver.scanRootElementHook(XML11NSDocumentScannerImpl.java:889)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3104)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:922)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.next(XML11NSDocumentScannerImpl.java:852)
    at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:554)
    at StaxSucks.parse(StaxSucks.java:26)
    at StaxSucks.main(StaxSucks.java:54)
dims@dims-laptop-520:~/test$ java -cp .:xercesImpl.jar:xml-apis.jar StaxSucks
Starting XML1.0
Stack is empty:true
Starting XML1.1
Stack is empty:true

关于java - 为什么 STAX 解析器认为这是有效的 XML 1.0 而不是 1.1？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10727288/