<b>java中通过xpath处理含有命名空间</b>[Java编程]

声明:以下的测试是用的jdk1.4.2,xalan7.0关于以下xml文档片断: <ML:MREML xmlns:ML="MREML">
<EnvelopEntity>
<EnvelopID>GUID2006102000002</EnvelopID>
<EnvelopVersion>1.0.1R</EnvelopVersion>
<ExchangeTime>2006-10-25 13:12:10</ExchangeTime>
<SendFrom>
<SFID>SOBEY_NEWS</SFID>
<SFDescription>SOBEY新闻系统</SFDescription>
</SendFrom>
<SendTo>
<STID>DAYANG_MAM</STID>
<STDescription>DAYANG媒资系统</STDescription>
</SendTo>
<Priority>2</Priority>
<EntityInfo>
<EntityID>REQUEST_ID_01</EntityID>
<EntityType>4</EntityType>
</EntityInfo>
<EntityInfo>
<EntityID>节目GUID</EntityID>
<EntityType>3</EntityType>
</EntityInfo>
<EntityInfo>
<EntityID>管理信息实体ID</EntityID>
<EntityType>2</EntityType>
</EntityInfo>
</EnvelopEntity>
</ML:MREML >
关于上述含有命名空间的xml文档,假如想通过xpath查找EnvelopID的值,有两种方法:1.通过操纵xpath的函数local-name（）

如上述查找内容的xpath表达式可以写为://*[local-name（）='MREML']/EnvelopEntity/EnvelopID/text（）

2.通过在java程序中处理上述文档的命名空间是定义的,假如要使xpath表达式能精确地被解析需求在java程序中成立起prefix和uri二者的映射关系
public static Node parseXPath(String expression, Object obj, QName qname)
throws Exception {
javax.xml.xpath.XPath xpath = javax.xml.xpath.XPathFactory.newInstance().newXPath();
xpath.setNamespaceContext(getNamespaceContext());
if (qname.equals(XPathConstants.NODE))
return (Node) xpath.evaluate(expression, obj, qname);
return null;
}

public static NamespaceContext getNamespaceContext() throws Exception {
return new NamespaceContext() {
public String getNamespaceURI(String prefix) {
/*
// 一种方法:
//这里可以采取配置文件的方法,先将所需求利用的xmlNamespace配置好,
//采取注册的方法供利用利用,这种方法效率应当高一些,不用每次都要从文档中提取namespace
//不过没有第二种便利
String uri;
if (prefix.equalsIgnoreCase("ML"))
uri = "MREML";
else if (prefix.equalsIgnoreCase("RE"))
uri = "http://herry.com.cn";
else if (prefix.equalsIgnoreCase("RID"))
uri = "ResourceID";
else if (prefix.equalsIgnoreCase("RUI"))
uri = "ResourceUniqueID";
else if (prefix.equalsIgnoreCase("RMDI"))
uri = "ResourceMetaDataInfo";
else
uri = null;
System.out.println(ParseXMLUtil.class + "::getNamespaceURI:prefix= " + prefix);
return uri;
*/
/*
// 别的一种方法: 通过PrefixResolver来提取出prefix和Namespace的对应关系
final PrefixResolver resolver =
new PrefixResolverDefault(doc.getDocumentElement());

return resolver.getNamespaceForPrefix(prefix);

*/

// Dummy implementation - not used!
public java.util.Iterator getPrefixes(String val) {
return null;
}

// Dummy implemenation - not used!
public String getPrefix(String uri) {
return null;
}
};
}
若要查找ResourceUniqueID的值,则xpath应当书写为://ML:MREML/ML:ResourceEntity/RMDI:ResourceMetaDataInfo/RMDI:ResourceID/RUI:ResourceUniqueID/text（）

这里的ML（prefix）和URI（MERML）等已经通过

关于含有默许命名空间地文档假如采取NamespaceContext的方法,行将prefix和uri已经映射起来,如关于以下的文档:
<MREML xmlns="MREML"><ResourceEntity >
<ResourceMetaDataInfo>
<ResourceID xmlns="ResourceID">
<RUI:ResourceUniqueID xmlns:RUI="ResourceUniqueID">节目GUID</RUI:ResourceUniqueID>
<UserDefID>UserDefID填写节目代码</UserDefID>
</ResourceID>
<Title>
<ResourceName>911新闻素材</ResourceName>
</Title>
<ResourceType>1</ResourceType>
<Subject>
<KeyWords>911 攻击</KeyWords>
</Subject>
<Description>
<ContentDescription>美国遭受911攻击现场30S画面及同期声素材</ContentDescription>
<Column>
<ColumnName>本日世界</ColumnName>
</Column>
</Description>
<Date>
<CreateDate>2006-10-25 13:12:10</CreateDate>
</Date>
<Format>
<TotalLength>00:04:35:12</TotalLength>
<NumberofElements>2</NumberofElements>
<MarkPoint>
<StartPoint>00:00:00:05</StartPoint>
<EndPoint>00:04:35:10</EndPoint>
</MarkPoint>
</Format>
</ResourceMetaDataInfo>
</ResourceEntity>
</MREML>

若要查找ResourceUniqueID的值,则xpath应当书写为://ML:MREML/ML:ResourceEntity/RMDI:ResourceMetaDataInfo/RMDI:ResourceID/RUI:ResourceUniqueID/text（）

这里的ML（prefix）和URI（MERML）等已经通过
if (prefix.equalsIgnoreCase("ML"))
uri = "MREML";
else if (prefix.equalsIgnoreCase("RE"))
uri = "http://herry.com.cn";
else if (prefix.equalsIgnoreCase("RID"))
uri = "ResourceID";
else if (prefix.equalsIgnoreCase("RUI"))
uri= "ResourceUniqueID";
else if (prefix.equalsIgnoreCase("RMDI"))
uri = "ResourceMetaDataInfo";
else
uri = null;
映射.

此中的ML和RMDI都是default namespace,它的作用范围包含它的子元素,直至有新的default namespace呈现为止.而namespace只对它自身起作用.如将上述文档中:<ResourceMetaDataInfo>
<ResourceID xmlns="ResourceID">
改成:
<RMDI:ResourceMetaDataInfo xmlns:RMDI=” ResourceMetaDataInfo”>
<ResourceID>
…
…
</ RMDI:ResourceMetaDataInfo>
查找ResourceUniqueID的值,则xpath应当改成://ML:MREML/ML:ResourceEntity/RMDI:ResourceMetaDataInfo/ResourceID/RUI:ResourceUniqueID/text（）

大家也可参考这篇文章:
http://blog.davber.com/2006/09/17/xpath-with-namespaces-in-java/