错误：未声明前缀“ xsi”的命名空间。

Question

为什么会出现此错误：

错误：未声明前缀“ xsi”的命名空间。

这是我的Java代码：

package com.emp.ma.jbl.nsnhlrspmlpl.nsnhlrspmlpl.internal.action;
import com.emp.ma.util.xml.XMLDocument;
import com.emp.ma.util.xml.XMLDocumentBuilder;

 public class yay {            
        public static void main(String[] args) {
            XMLDocument xmldoc = XMLDocumentBuilder.newDocument().addRoot("spml:modifyRequest");
            xmldoc.gotoRoot().addTag("modification").addText("");
            xmldoc.gotoChild("modification").addTag("valueObject").addText("");
            xmldoc.gotoChild("valueObject").addAttribute("xsi:type","halo");
            System.out.println(xmldoc);
        }            
    }

直到我尝试引发转换器异常，同时将XML文件转换为HTML进行实验时，这段代码才能正常运行。我需要创建一个格式为xml的文件：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<spml:modifyRequest>   
  <modification>
    <valueObject xsi:type="halo">
    </valueObject>   
  </modification>
</spml:modifyRequest>

我已经从代码中删除了转换器部分，但是在eclipse中却遇到了这个错误：

 ERROR:  'Namespace for prefix 'xsi' has not been declared.'
    Exception in thread "main" com.emp.ma.util.xml.XMLDocumentException: java.lang.RuntimeException: Namespace for prefix 'xsi' has not been declared.
        at com.emp.ma.util.xml.XMLDocumentImpl.toResult(XMLDocumentImpl.java:1244)
        at com.emp.ma.util.xml.XMLDocumentImpl.toStream(XMLDocumentImpl.java:1314)
        at com.emp.ma.util.xml.XMLDocumentImpl.toString(XMLDocumentImpl.java:1336)
        at com.emp.ma.util.xml.XMLDocumentImpl.toString(XMLDocumentImpl.java:1325)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at com.emp.ma.util.xml.XMLDocumentBuilder$XMLDocumentHandler.invoke(XMLDocumentBuilder.java:55)
        at $Proxy1.toString(Unknown Source)
        at java.lang.String.valueOf(Unknown Source)
        at java.io.PrintStream.println(Unknown Source)
        at com.emp.ma.jbl.nsnhlrspmlpl.nsnhlrspmlpl.internal.action.yay.main(yay.java:13)
    Caused by: javax.xml.transform.TransformerException: java.lang.RuntimeException: Namespace for prefix 'xsi' has not been declared.
        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 com.emp.ma.util.xml.XMLDocumentImpl.toResult(XMLDocumentImpl.java:1242)
        ... 12 more
    Caused by: java.lang.RuntimeException: Namespace for prefix 'xsi' has not been declared.
        at com.sun.org.apache.xml.internal.serializer.SerializerBase.getNamespaceURI(Unknown Source)
        at com.sun.org.apache.xml.internal.serializer.SerializerBase.addAttribute(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
        at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
    ... 15 more

由于这一例外，我被困住了，而且我不知道如何撤消它。请帮忙。就像我说的那样，在尝试我的这个实验之前，它运行正常，如果可能的话，我该如何删除该变压器集成。我也尝试过更改工作区-仍然无法正常工作。

Answer 1

为了使XML文档格式正确，必须声明所有使用的名称空间前缀。

只需xsi在XML的根元素上声明名称空间前缀，

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<spml:modifyRequest xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">   
  <modification>
    <valueObject xsi:type="halo">
    </valueObject>   
  </modification>
</spml:modifyRequest>

这样您的错误就会消失。

请注意，您同样必须定义spml名称空间前缀。