如何在 Android 上将 Java XPath 用于 KML 文件和命名空间
How to use Java XPath with KML files and namespaces on Android
我正在为如何在包含新 gx:Track 和 gx:coord 标签的 KML 文件上使用 XPath 而苦恼。问题在于如何将 XPath 与 Android.
下的命名空间一起使用
我看过很多例子，包括这些
https://www.ibm.com/developerworks/library/x-nmspccontext/index.html
https://howtodoinjava.com/xml/xpath-namespace-resolution-example/
XPath with namespace in Java
- NamespaceContext and using namespaces with XPath
但我似乎连这些例子都无法发挥作用。
以下代码和输出说明了我的问题：
public App() {
super();
try {
test( testDoc1() );
test( testDoc2() );
} catch( Exception e ) {
e.printStackTrace();
} finally {
Log.d( "TEST-FINISHED", "test is finished" );
}
}
private String toXmlString( Document document ) throws TransformerException {
DOMSource domSource = new DOMSource( document );
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult( writer );
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.transform( domSource, result );
return writer.toString();
}
private Document testDoc1() throws ParserConfigurationException {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware( true );
Document mDocument = documentBuilderFactory.newDocumentBuilder().newDocument();
String XMLNS_NAMESPACE_URI = "http://www.w3.org/2000/xmlns/";
Element mKmlElement = mDocument.createElement( "kml" );
mKmlElement.setAttributeNS( XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2" );
mKmlElement.setAttributeNS( XMLNS_NAMESPACE_URI, "xmlns:gx", "http://www.google.com/kml/ext/2.2" );
mDocument.appendChild( mKmlElement );
Element mPlacemarkElement = mDocument.createElement( "Placemark" );
mKmlElement.appendChild( mPlacemarkElement );
Element gxTrackElement = mDocument.createElement( "gx:Track" );
mPlacemarkElement.appendChild( gxTrackElement );
Element gxCoordElement = mDocument.createElement( "gx:coord" );
gxCoordElement.setTextContent( "-122.207881 37.371915 156.000000" );
gxTrackElement.appendChild( gxCoordElement );
return mDocument;
}
private Document testDoc2() throws ParserConfigurationException, IOException, SAXException {
String kmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><kml xmlns=\"http://www.opengis.net/kml/2.2\" xmlns:gx=\"http://www.google.com/kml/ext/2.2\"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>";
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware( true );
Document mDocument = documentBuilderFactory.newDocumentBuilder().parse( new InputSource( new StringReader( kmlString ) ) );
return mDocument;
}
private void test( Document mDocument ) throws Exception {
String xml = toXmlString( mDocument );
Log.d( "TEST-XML", xml );
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext( new NamespaceContext() {
@Override
public String getNamespaceURI( String prefix ) {
switch( prefix ) {
case XMLConstants.DEFAULT_NS_PREFIX:
return "http://www.opengis.net/kml/2.2";
case "gx":
return "http://www.google.com/kml/ext/2.2";
}
return XMLConstants.NULL_NS_URI;
}
@Override
public String getPrefix( String namespaceURI ) {
return null;
}
@Override
public Iterator getPrefixes( String namespaceURI ) {
return null;
}
} );
NodeList result1 = (NodeList) xPath.evaluate( "/kml", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT1", String.valueOf( result1.getLength() ) );
NodeList result2 = (NodeList) xPath.evaluate( "/kml/Placemark", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT2", String.valueOf( result2.getLength() ) );
NodeList result3 = (NodeList) xPath.evaluate( "/kml/Placemark/gx:Track", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT3", String.valueOf( result3.getLength() ) );
}
test()方法执行3次XPathstatements/patterns，对两个测试文档各调用一次。这两份文件是用不同的方法构建的，但内容应该是相同的。但是，我从 3 个 XPath 语句中得到的结果是不同的。
这些是文档 1 的结果：
2018-11-17 17:51:28.289 22837-22837/ca.csdesigninc.offroadtracker D/TEST-XML: <?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>
2018-11-17 17:51:28.324 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT1: 1
2018-11-17 17:51:28.334 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT2: 1
2018-11-17 17:51:28.343 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT3: 0
这些是文档 2 的结果：
2018-11-17 17:51:28.348 22837-22837/ca.csdesigninc.offroadtracker D/TEST-XML: <?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>
2018-11-17 17:51:28.358 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT1: 0
2018-11-17 17:51:28.363 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT2: 0
2018-11-17 17:51:28.372 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT3: 0
至少有两个问题：
既然2个文档是一样的（我觉得），为什么测试的结果不一样呢？ （即，前 2 个 XPath 语句在文档 1 中成功，但在文档 2 中均不成功。）
为什么第三个 XPath 语句在文档 1 和文档 2 中都找不到 gx:Track 元素？
更新：这个问题似乎与
有关
xmlns="http://www.opengis.net/kml/2.2"
包含在文档 2 中。如果我删除它，前 2 个 XPath 测试的结果是正确的（对于两个文档）- 实际上 XPath 测试 3 现在可以在文档 2 上运行。不幸的是，我仍然没有无法处理此行为。
我可能遗漏了一些明显的东西，非常感谢任何帮助。
不同之处在于名称空间。 XML 的生成方式以及在 XPath 中 selecting 内容的时间。
不幸的是，很难看出差异，因为 XML 恰好被 toXmlString() 序列化为 testDoc1() 与 in- 的状态不完全匹配记忆文件。
当您构建 kml 元素时，使用 createElement() 它会创建一个绑定到 "no namespace" 的元素。然后，您添加了命名空间属性，这些属性在使用 toXmlString() 进行序列化时恰好出现，并使 kml 元素看起来位于 http://www.opengis.net/kml/2.2 命名空间中。
如果您要将 XML 编组回新的 Document 对象，kml 元素 将绑定 到该命名空间.但是，该元素的当前内存中对象不是。
您可以通过添加一些额外的诊断 println 消息来观察这一点：
NodeList result1 = (NodeList) xPath.evaluate("/kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
您可以往返您的 XML 并观察它在编组序列化 XML:
时的行为不同
private void test(Document mDocument) throws Exception {
String xml = toXmlString(mDocument);
System.out.println( xml);
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
mDocument = documentBuilderFactory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
但是，这是作弊。您真正想要做的是确保首先正确创建元素。当您创建要绑定到命名空间的元素时，请使用 createElementNS() 方法，如 createElement():
的 JavaDoc 注释中所示
To create an element with a qualified name and namespace URI, use the createElementNS method.
因此，要创建绑定到 http://www.opengis.net/kml/2.2 命名空间的元素，您需要使用：
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "kml");
和：
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "Placemark");
gx:Track 元素也是如此：
Element gxTrackElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2","gx:Track");
一旦您的文档对象真正相等且正确，您就需要调整您的 XPath。
使用 XPath，如果不应用名称空间前缀，它将 select 个元素绑定到 "no namespace"。因此，/kml 将仅 select kml 未绑定到命名空间的元素。但是由于您的 kml 元素绑定到 http://www.opengis.net/kml/2.2 命名空间，它不会 select 它们。
在覆盖 getNamespaceURI() 函数时，您可以为 Google KML 扩展命名空间保留 gx，然后默认任何其他命名空间前缀解析为 http://www.opengis.net/kml/2.2:
@Override
public String getNamespaceURI(String prefix) {
return "gx".equals(prefix) ? "http://www.google.com/kml/ext/2.2" : "http://www.opengis.net/kml/2.2";
}
然后，调整您的 XPath 语句以对这些 KML 元素使用前缀。如果你使用上面的代码，你使用什么前缀都没有关系。 gx 以外的任何内容都将 return http://www.opengis.net/kml/2.2 命名空间。
NodeList result1 = (NodeList) xPath.evaluate("/k:kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
NodeList result2 = (NodeList) xPath.evaluate("/k:kml/k:Placemark", mDocument, XPathConstants.NODESET);
System.out.println( String.valueOf(result2.getLength()));
NodeList result3 = (NodeList) xPath.evaluate("/k:kml/k:Placemark/gx:Track", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result3.getLength()));
综合起来：
public App() {
super();
try {
test( testDoc1() );
test( testDoc2() );
} catch( Exception e ) {
e.printStackTrace();
} finally {
Log.d( "TEST-FINISHED", "test is finished" );
}
}
private String toXmlString(Document document) throws TransformerException {
DOMSource domSource = new DOMSource(document);
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult(writer);
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.transform(domSource, result);
return writer.toString();
}
private Document testDoc1() throws ParserConfigurationException {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
Document mDocument = documentBuilderFactory.newDocumentBuilder().newDocument();
String XMLNS_NAMESPACE_URI = "http://www.w3.org/2000/xmlns/";
//Element mKmlElement = mDocument.createElement("kml");
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "kml");
//mKmlElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2");
mKmlElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns:gx", "http://www.google.com/kml/ext/2.2");
mDocument.appendChild(mKmlElement);
//Element mPlacemarkElement = mDocument.createElement("Placemark");
Element mPlacemarkElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "Placemark");
//mPlacemarkElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2");
mKmlElement.appendChild(mPlacemarkElement);
//Element gxTrackElement = mDocument.createElement("gx:Track");
Element gxTrackElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2","gx:Track");
mPlacemarkElement.appendChild(gxTrackElement);
//Element gxCoordElement = mDocument.createElement("gx:coord");
Element gxCoordElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2", "gx:coord");
gxCoordElement.setTextContent("-122.207881 37.371915 156.000000");
gxTrackElement.appendChild(gxCoordElement);
return mDocument;
}
private Document testDoc2() throws ParserConfigurationException, IOException, SAXException {
String kmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><kml xmlns=\"http://www.opengis.net/kml/2.2\" xmlns:gx=\"http://www.google.com/kml/ext/2.2\"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>";
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
Document mDocument = documentBuilderFactory.newDocumentBuilder().parse(new
InputSource(new StringReader(kmlString)));
return mDocument;
}
private void test(Document mDocument) throws Exception {
String xml = toXmlString(mDocument);
System.out.println( xml);
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext(new NamespaceContext() {
@Override
public String getNamespaceURI(String prefix) {
return "gx".equals(prefix) ? "http://www.google.com/kml/ext/2.2" : "http://www.opengis.net/kml/2.2";
}
@Override
public String getPrefix(String namespaceURI) {
if ("http://www.google.com/kml/ext/2.2".equals(namespaceURI)) {
return "gx";
}
return null;
}
@Override
public Iterator getPrefixes(String namespaceURI) {
List<String> ns = new ArrayList<>();
ns.add("gx");
return ns.iterator();
}
});
NodeList result1 = (NodeList) xPath.evaluate("/k:kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
NodeList result2 = (NodeList) xPath.evaluate("/k:kml/k:Placemark", mDocument, XPathConstants.NODESET);
System.out.println( String.valueOf(result2.getLength()));
NodeList result3 = (NodeList) xPath.evaluate("/k:kml/k:Placemark/gx:Track", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result3.getLength()));
}
我正在为如何在包含新 gx:Track 和 gx:coord 标签的 KML 文件上使用 XPath 而苦恼。问题在于如何将 XPath 与 Android.
下的命名空间一起使用我看过很多例子，包括这些
https://www.ibm.com/developerworks/library/x-nmspccontext/index.html
https://howtodoinjava.com/xml/xpath-namespace-resolution-example/
XPath with namespace in Java
- NamespaceContext and using namespaces with XPath
但我似乎连这些例子都无法发挥作用。
以下代码和输出说明了我的问题：
public App() {
super();
try {
test( testDoc1() );
test( testDoc2() );
} catch( Exception e ) {
e.printStackTrace();
} finally {
Log.d( "TEST-FINISHED", "test is finished" );
}
}
private String toXmlString( Document document ) throws TransformerException {
DOMSource domSource = new DOMSource( document );
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult( writer );
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.transform( domSource, result );
return writer.toString();
}
private Document testDoc1() throws ParserConfigurationException {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware( true );
Document mDocument = documentBuilderFactory.newDocumentBuilder().newDocument();
String XMLNS_NAMESPACE_URI = "http://www.w3.org/2000/xmlns/";
Element mKmlElement = mDocument.createElement( "kml" );
mKmlElement.setAttributeNS( XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2" );
mKmlElement.setAttributeNS( XMLNS_NAMESPACE_URI, "xmlns:gx", "http://www.google.com/kml/ext/2.2" );
mDocument.appendChild( mKmlElement );
Element mPlacemarkElement = mDocument.createElement( "Placemark" );
mKmlElement.appendChild( mPlacemarkElement );
Element gxTrackElement = mDocument.createElement( "gx:Track" );
mPlacemarkElement.appendChild( gxTrackElement );
Element gxCoordElement = mDocument.createElement( "gx:coord" );
gxCoordElement.setTextContent( "-122.207881 37.371915 156.000000" );
gxTrackElement.appendChild( gxCoordElement );
return mDocument;
}
private Document testDoc2() throws ParserConfigurationException, IOException, SAXException {
String kmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><kml xmlns=\"http://www.opengis.net/kml/2.2\" xmlns:gx=\"http://www.google.com/kml/ext/2.2\"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>";
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware( true );
Document mDocument = documentBuilderFactory.newDocumentBuilder().parse( new InputSource( new StringReader( kmlString ) ) );
return mDocument;
}
private void test( Document mDocument ) throws Exception {
String xml = toXmlString( mDocument );
Log.d( "TEST-XML", xml );
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext( new NamespaceContext() {
@Override
public String getNamespaceURI( String prefix ) {
switch( prefix ) {
case XMLConstants.DEFAULT_NS_PREFIX:
return "http://www.opengis.net/kml/2.2";
case "gx":
return "http://www.google.com/kml/ext/2.2";
}
return XMLConstants.NULL_NS_URI;
}
@Override
public String getPrefix( String namespaceURI ) {
return null;
}
@Override
public Iterator getPrefixes( String namespaceURI ) {
return null;
}
} );
NodeList result1 = (NodeList) xPath.evaluate( "/kml", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT1", String.valueOf( result1.getLength() ) );
NodeList result2 = (NodeList) xPath.evaluate( "/kml/Placemark", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT2", String.valueOf( result2.getLength() ) );
NodeList result3 = (NodeList) xPath.evaluate( "/kml/Placemark/gx:Track", mDocument, XPathConstants.NODESET );
Log.d( "TEST-RESULT3", String.valueOf( result3.getLength() ) );
}
test()方法执行3次XPathstatements/patterns，对两个测试文档各调用一次。这两份文件是用不同的方法构建的，但内容应该是相同的。但是，我从 3 个 XPath 语句中得到的结果是不同的。
这些是文档 1 的结果：
2018-11-17 17:51:28.289 22837-22837/ca.csdesigninc.offroadtracker D/TEST-XML: <?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml> 2018-11-17 17:51:28.324 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT1: 1 2018-11-17 17:51:28.334 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT2: 1 2018-11-17 17:51:28.343 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT3: 0
这些是文档 2 的结果：
2018-11-17 17:51:28.348 22837-22837/ca.csdesigninc.offroadtracker D/TEST-XML: <?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml> 2018-11-17 17:51:28.358 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT1: 0 2018-11-17 17:51:28.363 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT2: 0 2018-11-17 17:51:28.372 22837-22837/ca.csdesigninc.offroadtracker D/TEST-RESULT3: 0
至少有两个问题：
既然2个文档是一样的（我觉得），为什么测试的结果不一样呢？ （即，前 2 个 XPath 语句在文档 1 中成功，但在文档 2 中均不成功。）
为什么第三个 XPath 语句在文档 1 和文档 2 中都找不到 gx:Track 元素？
更新：这个问题似乎与
有关xmlns="http://www.opengis.net/kml/2.2"包含在文档 2 中。如果我删除它，前 2 个 XPath 测试的结果是正确的（对于两个文档）- 实际上 XPath 测试 3 现在可以在文档 2 上运行。不幸的是，我仍然没有无法处理此行为。
我可能遗漏了一些明显的东西，非常感谢任何帮助。
不同之处在于名称空间。 XML 的生成方式以及在 XPath 中 selecting 内容的时间。
不幸的是，很难看出差异，因为 XML 恰好被 toXmlString() 序列化为 testDoc1() 与 in- 的状态不完全匹配记忆文件。
当您构建 kml 元素时，使用 createElement() 它会创建一个绑定到 "no namespace" 的元素。然后，您添加了命名空间属性，这些属性在使用 toXmlString() 进行序列化时恰好出现，并使 kml 元素看起来位于 http://www.opengis.net/kml/2.2 命名空间中。
如果您要将 XML 编组回新的 Document 对象，kml 元素 将绑定 到该命名空间.但是，该元素的当前内存中对象不是。
您可以通过添加一些额外的诊断 println 消息来观察这一点：
NodeList result1 = (NodeList) xPath.evaluate("/kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
您可以往返您的 XML 并观察它在编组序列化 XML:
时的行为不同private void test(Document mDocument) throws Exception {
String xml = toXmlString(mDocument);
System.out.println( xml);
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
mDocument = documentBuilderFactory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
但是，这是作弊。您真正想要做的是确保首先正确创建元素。当您创建要绑定到命名空间的元素时，请使用 createElementNS() 方法，如 createElement():
To create an element with a qualified name and namespace URI, use the
createElementNSmethod.
因此，要创建绑定到 http://www.opengis.net/kml/2.2 命名空间的元素，您需要使用：
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "kml");
和：
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "Placemark");
gx:Track 元素也是如此：
Element gxTrackElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2","gx:Track");
一旦您的文档对象真正相等且正确，您就需要调整您的 XPath。
使用 XPath，如果不应用名称空间前缀，它将 select 个元素绑定到 "no namespace"。因此，/kml 将仅 select kml 未绑定到命名空间的元素。但是由于您的 kml 元素绑定到 http://www.opengis.net/kml/2.2 命名空间，它不会 select 它们。
在覆盖 getNamespaceURI() 函数时，您可以为 Google KML 扩展命名空间保留 gx，然后默认任何其他命名空间前缀解析为 http://www.opengis.net/kml/2.2:
@Override
public String getNamespaceURI(String prefix) {
return "gx".equals(prefix) ? "http://www.google.com/kml/ext/2.2" : "http://www.opengis.net/kml/2.2";
}
然后，调整您的 XPath 语句以对这些 KML 元素使用前缀。如果你使用上面的代码，你使用什么前缀都没有关系。 gx 以外的任何内容都将 return http://www.opengis.net/kml/2.2 命名空间。
NodeList result1 = (NodeList) xPath.evaluate("/k:kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
NodeList result2 = (NodeList) xPath.evaluate("/k:kml/k:Placemark", mDocument, XPathConstants.NODESET);
System.out.println( String.valueOf(result2.getLength()));
NodeList result3 = (NodeList) xPath.evaluate("/k:kml/k:Placemark/gx:Track", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result3.getLength()));
综合起来：
public App() {
super();
try {
test( testDoc1() );
test( testDoc2() );
} catch( Exception e ) {
e.printStackTrace();
} finally {
Log.d( "TEST-FINISHED", "test is finished" );
}
}
private String toXmlString(Document document) throws TransformerException {
DOMSource domSource = new DOMSource(document);
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult(writer);
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.transform(domSource, result);
return writer.toString();
}
private Document testDoc1() throws ParserConfigurationException {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
Document mDocument = documentBuilderFactory.newDocumentBuilder().newDocument();
String XMLNS_NAMESPACE_URI = "http://www.w3.org/2000/xmlns/";
//Element mKmlElement = mDocument.createElement("kml");
Element mKmlElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "kml");
//mKmlElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2");
mKmlElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns:gx", "http://www.google.com/kml/ext/2.2");
mDocument.appendChild(mKmlElement);
//Element mPlacemarkElement = mDocument.createElement("Placemark");
Element mPlacemarkElement = mDocument.createElementNS("http://www.opengis.net/kml/2.2", "Placemark");
//mPlacemarkElement.setAttributeNS(XMLNS_NAMESPACE_URI, "xmlns", "http://www.opengis.net/kml/2.2");
mKmlElement.appendChild(mPlacemarkElement);
//Element gxTrackElement = mDocument.createElement("gx:Track");
Element gxTrackElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2","gx:Track");
mPlacemarkElement.appendChild(gxTrackElement);
//Element gxCoordElement = mDocument.createElement("gx:coord");
Element gxCoordElement = mDocument.createElementNS("http://www.google.com/kml/ext/2.2", "gx:coord");
gxCoordElement.setTextContent("-122.207881 37.371915 156.000000");
gxTrackElement.appendChild(gxCoordElement);
return mDocument;
}
private Document testDoc2() throws ParserConfigurationException, IOException, SAXException {
String kmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><kml xmlns=\"http://www.opengis.net/kml/2.2\" xmlns:gx=\"http://www.google.com/kml/ext/2.2\"><Placemark><gx:Track><gx:coord>-122.207881 37.371915 156.000000</gx:coord></gx:Track></Placemark></kml>";
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
Document mDocument = documentBuilderFactory.newDocumentBuilder().parse(new
InputSource(new StringReader(kmlString)));
return mDocument;
}
private void test(Document mDocument) throws Exception {
String xml = toXmlString(mDocument);
System.out.println( xml);
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext(new NamespaceContext() {
@Override
public String getNamespaceURI(String prefix) {
return "gx".equals(prefix) ? "http://www.google.com/kml/ext/2.2" : "http://www.opengis.net/kml/2.2";
}
@Override
public String getPrefix(String namespaceURI) {
if ("http://www.google.com/kml/ext/2.2".equals(namespaceURI)) {
return "gx";
}
return null;
}
@Override
public Iterator getPrefixes(String namespaceURI) {
List<String> ns = new ArrayList<>();
ns.add("gx");
return ns.iterator();
}
});
NodeList result1 = (NodeList) xPath.evaluate("/k:kml", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result1.getLength()));
System.out.println("Namespace URI: " + result1.item(0).getNamespaceURI());
System.out.println("Prefix: " + result1.item(0).getPrefix());
NodeList result2 = (NodeList) xPath.evaluate("/k:kml/k:Placemark", mDocument, XPathConstants.NODESET);
System.out.println( String.valueOf(result2.getLength()));
NodeList result3 = (NodeList) xPath.evaluate("/k:kml/k:Placemark/gx:Track", mDocument, XPathConstants.NODESET);
System.out.println(String.valueOf(result3.getLength()));
}