📄 xpath_getabselem.htm
字号:
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>Finding Elements by Absolute Location in a DOM Document Using XPath (Java Developers Almanac Example)
</TITLE>
<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
<META CONTENT="Addison-Wesley/Patrick Chan" NAME="OWNER">
<META CONTENT="3/20/02" NAME="revision">
<META CONTENT="no-cache" HTTP-EQUIV="Pragma">
<LINK href="/almanac.css" media="screen" type="text/css" rel="stylesheet">
</HEAD>
<BODY>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD></TD>
</TR>
</TABLE>
<br>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD></TD>
</TR>
<TR>
<TD rowspan="3"><A HREF="/?l=ex"><IMG BORDER="0" ALIGN="BOTTOM" HSPACE="10" SRC="/egs/almanac14a.jpg"></A></TD><TD VALIGN="top">
<h1>The Java Developers Almanac 1.4</h1>
<br>
Order this book from <a href="/cgi-bin/scripts/redirect.pl?l=ex&url=http://www.amazon.com/exec/obidos/ASIN/0201752808/xeo">Amazon</a>.
</TD>
</TR>
<TR>
<TD align="right" valign="bottom">
<FORM method="get" action="/cgi-bin/search/find.pl">
<INPUT size="25" name="words" type="text"><INPUT value="Search" type="submit">
</FORM>
</TD>
</TR>
</TABLE>
<HR color="#6666cc">
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD valign="top"><script type="text/javascript">
<!--
google_ad_client = "pub-6001183370374757";
google_ad_width = 120;
google_ad_height = 600;
google_ad_format = "120x600_as";
google_ad_channel = "4777242811";
google_ad_type = "text_image";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "6666CC";
google_color_url = "6666CC";
google_color_text = "000000";
//--></script><script src="http://pagead2.googlesyndication.com/pagead/show_ads.js" type="text/javascript"></script></TD><TD> </TD><TD valign="top">
<DIV ALIGN="LEFT">
<A HREF="/">Home</A>
>
<A HREF="../index.html">List of Packages</A>
>
<A HREF="../org.w3c.dom/pkg.html">org.w3c.dom</A><font color="#666666" class="xsmall-font">
[30 examples]
</font>
>
<B><A HREF="../org.w3c.dom/pkg.html#XPath">XPath</A></B><font color="#666666" class="xsmall-font">
[5 examples]
</font>
</DIV><P>
<h3>e1074. Finding Elements by Absolute Location in a DOM Document Using XPath</h3>
XPath is an expression language for selecting nodes in an XML file.
For example, the XPath expression <code>/a/b</code> selects all <code>b</code>
elements under the root element <code>a</code>. This example demonstrates
some common XPath expressions for selecting elements based on the
document root. For examples of XPath expressions relative to a
particular node, see <a href="../org.w3c.dom/xpath_GetRelElem.html" class="eglink"><b>eX</b> X</a>. For
more information about XPath, see the specification at
<a href="http://www.w3c.org/TR/xpath">http://www.w3c.org/TR/xpath</a>.
The XPath package used in this example selects nodes in a DOM
document. Hence, the XML file is first parsed into a DOM document and
the XPath expression is then applied to the DOM document. The result
of an XPath expression is shown next to the expression; the numbers
are ids of elements in the sample file shown at the end of this
example.
<P> Note: This example uses the XPath packages (<code>org.apache.xpath.*</code>)
available in J2SE 1.4. However, these packages are not yet part of
the Java 2 API and so this example may not work in future versions of
J2SE.
<pre> // Get the root element (without specifying its name)
String xpath = "/*"; // 1
// Get the root element (using its name)
xpath = "/root"; // 1
// Get all elements directly under the root
xpath = "/root/*"; // 2 8 12
// Get all e elements directly under the root
xpath = "/root/e"; // 12
// Get all e elements in the document
xpath = "//e"; // 4 6 10 11 12
// Get all non-e elements in the document
xpath = "//*[name() != 'e']"; // 1 2 3 5 7 8 9
// Get all e elements directly under an elem1 element
xpath = "//elem1/e"; // 10 11
// Get all e elements anywhere under an elem1 element
xpath = "//elem1//e"; // 4 6 10 11
// Get all elements with at least one child element
xpath = "//*[*]"; // 1 2 3 5 8
// Get all elements without a child element
xpath = "//*[not(*)]"; // 4 6 7 9 10 11 12
// Get all elements with at least one child e element
xpath = "//*[e]"; // 1 3 5 8
// Get all elements with more than one child e elements
xpath = "//*[count(e)>1]"; // 8
// Get all non-e elements without an e child element
xpath = "//*[not(e) and name() != 'e']"; // 2 7 9
// Get all <font color="#0066ff"><i>level-4</i></font> e elements (the root being at level 1)
xpath = "/*/*/*/e"; // 4
// Get all elements with more than one child e elements
xpath = "//*[count(e)>1]"; // 8
</pre>
XPath 1.0 does not support regular expressions to match element names.
However, it is possible to perform some very simple matches on element
names.
<pre> // Get all elements whose name starts with el
xpath = "//*[starts-with(name(), 'el')]"; // 2 3 5 7 8 9
// Get all elements whose name contains with lem1
xpath = "//*[contains(name(), 'lem1')]"; // 2 8
</pre>
Sets of elements can also be combined using the union operator <code>|</code>
<pre> // Get all e elements directly under either the root or an elem2 element
xpath = "/*/e | //elem2/e"; // 4 12
</pre>
Elements are returned in <font color="#0066ff"><i>document order</i></font>, that is, if the
location of <code>A</code>'s start tag appears before the location of <code>B</code>'s
start tag in the XML document, element <code>A</code> is returned before
element <code>B</code>. Moreover, the returned elements are unique.
<pre> // Read an XML document; this method is implemented in
// <a href="../javax.xml.parsers/BasicDom.html" class="eglink"><b>e510</b> The Quintessential Program to Create a DOM Document from an XML File</a>
Document doc = <font color="#0066ff"><i>parseXmlFile</i></font>(<font color="#0066ff"><i>"infilename.xml"</i></font>, <font color="#0066ff"><i>false</i></font>);
try {
// Get the matching elements
NodeList nodelist = org.apache.xpath.XPathAPI.selectNodeList(doc, xpath);
// Process the elements in the nodelist
for (int i=0; i<nodelist.getLength(); i++) {
// Get element
Element elem = (Element)nodelist.item(i);
}
} catch (javax.xml.transform.TransformerException e) {
}
</pre>
Here is the sample XML file used in the example:
<pre> <?xml version="1.0" encoding="UTF-8"?>
<root id="1">
<elem1 id="2">
<elem2 id="3">
<e id="4"/>
<elem3 id="5">
<e id="6"/>
</elem3>
<elem3 id="7"/>
</elem2>
</elem1>
<elem1 id="8">
<elem2 id="9"/>
<e id="10"/>
<e id="11"/>
</elem1>
<e id="12"/>
</root>
</pre>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td bgcolor="#6666cc" align="center"><font color="#ffffff">
<b>Related Examples</b></font></td>
</tr>
</table>
e1075. <a class="eglink" href="xpath_GetChildElem.html?l=rel">
Selecting from a Set of Child Elements in a DOM Document Using XPath
</a>
<br>
e1076. <a class="eglink" href="xpath_GetElemByText.html?l=rel">
Finding Elements by Content in a DOM Document Using XPath
</a>
<br>
e1077. <a class="eglink" href="xpath_GetElemById.html?l=rel">
Finding Elements by Id in a DOM Document Using XPath
</a>
<br>
e1078. <a class="eglink" href="xpath_GetElemByAttr.html?l=rel">
Finding Elements by Attributes in a DOM Document Using XPath
</a>
<br>
<table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td align="left">
<br>
See also:
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Adding%20and%20Removing%20Nodes">
Adding and Removing Nodes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Element%20Attributes">
Element Attributes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Elements">
Elements
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Getting%20Nodes">
Getting Nodes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Text%20Nodes">
Text Nodes
</a>
</td>
</tr>
</table>
<br>
<br>
<FONT class="xsmall-font">
© 2002 Addison-Wesley.
</FONT></TD><TD> </TD><TD valign="top"><A href="http://compositesw.com/devzone?ref=javaalmanac"><IMG alt="Click Here" height="600" width="120" border="0" src="/csw_oad_120x600_final.gif"></A></TD>
</TR>
</TABLE>
</BODY>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<META CONTENT="NO-CACHE" HTTP-EQUIV="PRAGMA">
</HEAD>
</HTML>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -