最近一直在学习XML的Xpath解析方式，据说是一个很简单的遍历XML文件的工具，类似于sql和Oracle的关系，但是找了很多都没有找到关于Java的Xpath代码，有的都是把W3School上的文档拷贝过来的，自己也尝试过去用Java去实现遍历，但是发现有的解释不理解，直到看到了这边外国人写的博客，让我瞬间明白了，真的感谢这位哥们。。。
下面是他的原文，我测试过几个列子，都是OK了，大家都懂英文，我就没有必要再翻译过来了，呵呵。
XPath is a language for finding information in an XML file. You can say that XPath is (sort of) sql for XML files. XPath is used to navigate through elements and attributes in an XML document. You can also use XPath totraverse through an XML file in Java.
XPath comes with powerful expressions that can be used to parse an xml document and retrieve relevant information.
For demo,let us consider an xml file that holds information of employees.
<?xml version="1.0"?>
<Employees>
<Employee emplid="1111" type="admin">
<firstname>John</firstname>
<lastname>Watson</lastname>
<age>30</age>
<email>johnwatson@sh.com</email>
</Employee>
<Employee emplid="2222" type="admin">
<firstname>Sherlock</firstname>
<lastname>Homes</lastname>
<age>32</age>
<email>sherlock@sh.com</email>
</Employee>
<Employee emplid="3333" type="user">
<firstname>Jim</firstname>
<lastname>Moriarty</lastname>
<age>52</age>
<email>jim@sh.com</email>
</Employee>
<Employee emplid="4444" type="user">
<firstname>Mycroft</firstname>
<lastname>Holmes</lastname>
<age>41</age>
<email>mycroft@sh.com</email>
</Employee>
</Employees>
I have saved this file at pathC:\employees.xml. We will use this xml file in our demo and will try to fetch useful information using XPath. Before we start lets check few facts from above xml file.
- There are 4 employees in our xml file
- Each employee has a unique employee id defined by attribute
emplid - Each employee also has an attribute
typewhich defines whether an employee is admin or user. - Each employee has four child nodes:
firstname,lastname,monotype; font-size: 0.9em; border: 0px; vertical-align: baseline; margin: 0px; padding: 0px 3px; color: #aa3333; background-color: #efefef;">ageandemail - Age is a number
Let’s get started…
1. Learning Java DOM Parsing API
In order to understand XPath,first we need to understand basics of DOM parsing in Java. Java provides powerful implementation of domparser in form of below API.
1.1 Creating a Java DOM XML Parser
First,we need to create a document builder usingDocumentBuilderFactoryclass. Just follow the code. It’s pretty much self explainatory.
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
//...
DocumentBuilderFactory builderFactory =
DocumentBuilderFactory.newInstance();
DocumentBuilder builder = null;
try {
builder = builderFactory.newDocumentBuilder();
} catch (ParserConfigurationException e) {
e.printStackTrace();
}
1.2 Parsing XML with a Java DOM Parser
Once we have a document builder object. We uses it to parse XML file and create a document object.
import org.w3c.dom.Document;
import java.io.IOException;
import org.xml.sax.SAXException;
//...
try {
Document document = builder.parse(
new FileInputStream("c:\\employees.xml"));
} catch (SAXException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
In above code,we are parsing an XML file from filesystem. Sometimes you might want to parse XML specified as String value instead of reading it from file. Below code comes handy to parse XML specified as String.
String xml = ...; Document xmlDocument = builder.parse(new ByteArrayInputStream(xml.getBytes()));