Java如何提取完整的XML块

Question

使用此XML示例:

<A>
  <B>
    <id>0</id>
  </B>
  <B>
    <id>1</id>
  </B>
</A>

我想要一个简单的方法来提取节点B的XML块,返回XML String:

<B>
  <id>1</id>
</B>

要检索此节点,我应该使用一些Java XPath库,如XOM或Java XPath,但我找不到如何获取完整的XML字符串.

我使用C#找到了两个等效的回答问题: C#如何提取完整的xml节点集以及如何从XML文档中提取XML块？

Answer 1

添加到lwburk的解决方案,要将DOM节点转换为字符串形式,您可以使用Transformer:

private static String nodeToString(Node node)
throws TransformerException
{
    StringWriter buf = new StringWriter();
    Transformer xform = TransformerFactory.newInstance().newTransformer();
    xform.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    xform.transform(new DOMSource(node), new StreamResult(buf));
    return(buf.toString());
}

完整的例子:

public static void main(String... args)
throws Exception
{
    String xml = "<A><B><id>0</id></B><B><id>1</id></B></A>";
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    Document doc = dbf.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));

    XPath xPath = XPathFactory.newInstance().newXPath();
    Node result = (Node)xPath.evaluate("A/B[id = '1']", doc, XPathConstants.NODE);

    System.out.println(nodeToString(result));
}

private static String nodeToString(Node node)
throws TransformerException
{
    StringWriter buf = new StringWriter();
    Transformer xform = TransformerFactory.newInstance().newTransformer();
    xform.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    xform.transform(new DOMSource(node), new StreamResult(buf));
    return(buf.toString());
}

Answer 2

引用第二个B元素所需的表达式应如下所示:

/*/B[id='1']

或者,如果目标节点位于文档中的未知位置,请使用:

//B[id='1']

完整的Java示例(假设XML在一个名为的文件中workbook.xml):

DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse("workbook.xml");
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile("//B[id='1']");        

NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
for (int i = 0; i < nodes.getLength(); i++) {
    System.out.println("[" + nodes.item(i) + "]");
}