StAX NullPointerException at xmlns=""

Question

目标

获取有关此问题的原因和解决方案/解决方法的建议。

问题

在 Stackoverflow Split 1GB Xml file using Java 中运行几乎相同的程序以拆分具有 xmlns="" 的 XML 文件时出现 NullPointerException，与 W3C specification 中一样。

XML

通过https://validator.w3.org/check 验证并确认格式正确。

<?xml version="1.0" encoding="UTF-8"?>
<EntityList>
  <Entity xmlns="">
  </Entity>
  <Entity xmlns="">
  </Entity>
</EntityList>

错误

JAXP: find factoryId =javax.xml.stream.XMLInputFactory
JAXP: loaded from fallback value: com.sun.xml.internal.stream.XMLInputFactoryImpl
JAXP: created new instance of class com.sun.xml.internal.stream.XMLInputFactoryImpl using ClassLoader: null
JAXP: find factoryId =javax.xml.transform.TransformerFactory
JAXP: loaded from fallback value: com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl
JAXP: created new instance of class com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl using ClassLoader: null
ERROR:  ''
Exception in thread "main" javax.xml.transform.TransformerException: java.lang.NullPointerException
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at stax.cursor.Demo.main(Demo.java:24)
Caused by: java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.NamespaceMappings.pushNamespace(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToStream.startPrefixMapping(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.emitFirstTag(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.flush(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.startElement(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.handleStartElement(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.bridge(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
    ... 3 more
---------
java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.NamespaceMappings.pushNamespace(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToStream.startPrefixMapping(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.emitFirstTag(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.flush(Unknown Source)
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.startElement(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.handleStartElement(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.bridge(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.StAXStream2SAX.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at stax.cursor.Demo.main(Demo.java:24)

环境

在 DELL latitude E7440 上的 Windows 10 Pro 64 位上使用 Java 7 和 8 进行测试

Java(TM) SE Runtime Environment (build 1.7.0_79-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.79-b02, mixed mode)

Java(TM) SE Runtime Environment (build 1.8.0_74-b02)
Java HotSpot(TM) 64-Bit Server VM (build 25.74-b02, mixed mode)

代码

package stax.cursor;

import java.io.File;
import java.io.FileReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stax.StAXSource;
import javax.xml.transform.stream.StreamResult;

public class Demo {

    public static void main(String[] args) throws Exception  {
        XMLInputFactory xif = XMLInputFactory.newInstance();
        XMLStreamReader xsr = xif.createXMLStreamReader(new FileReader("input.xml"));
        xsr.nextTag(); // Advance to statements element
        long count = 1;
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer t = tf.newTransformer();
        while(xsr.nextTag() == XMLStreamConstants.START_ELEMENT && xsr.getLocalName().toString().equals("Entity")) {
            File file = new File("out/" + java.lang.Long.valueOf(count++) + ".xml");
            t.transform(new StAXSource(xsr), new StreamResult(file));
        }
    }
} 

仅供参考

<?xml version="1.0" encoding="UTF-8"?>
<EntityList>
  <Entity xmlns="mailto:test.com">
  </Entity>
  <Entity>
  </Entity>
</EntityList>

此 XML 按预期拆分为两个 XML 文件。

1.xml

<?xml version="1.0" encoding="UTF-8"?><Entity xmlns="mailto:test.com">
  </Entity>

2.xml

<?xml version="1.0" encoding="UTF-8"?><Entity>
  </Entity>

Answer 1

这是 JDK 中的一个错误。您应该在http://bugs.java.com/ 提交错误报告

作为解决方法，您可以尝试使用替代的 Stax 实现。