Java uses XPath to query elements in XML

Querying elements in XML using XPath syntax in Java

1. Query the XML file for the Student.xml file

<?xml version= "1.0" encoding= "UTF-8"?>
<students>
<student class= "1201" >
<name>-Bruce Lee from </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1201" >
<name> Lin Chi-ling </name>
<sex> Women </sex>
<age>25</age>
</student>
<student class= "1201" >
<name> Lio Nio </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1302" >
<name> Zhang June </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1302" >
<name> Ning </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1302" >
<name> Lin Zhidong </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1302" >
<name> cuisine Xiao Feng </name>
<sex> Men </sex>
<age>25</age>
</student>
<student class= "1302" >
<name> Jolin Tsai </name>
<sex> Women </sex>
<age>25</age>
</student>
</students>

2. Use the XPath query steps as follows:

2.1 Create an instance of Xpathfactory:

Xpathfactory XF = new Xpathfactory ();

2.2 Get an XPath instance from an instance of Xpathfactory:

XPath x = Xf.newxpath ();

2.3 Query the XML using the evaluate () method of the XPath instance:

2.3.1 now cite the following two methods.

Specific Link: http://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPath.html

/*

Expression: The query statement for the XPath syntax.

Source: The origin of the *.xml of the input query

ReturnType: The types of returned results are: Xpathconstants.node (single Element), Xpathconstants.nodeset (collection of elements)

Specific return type link: http://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPathConstants.html

string evaluate (string Expression,inputsource source);

Object Evaluate (String expression,inputsource source,return returntype);

*/

2.3.1 Create a new Selectxml class:

Import Java.io.InputStream;

Import Org.xml.sax.InputSource;

Import Javax.xml.xpath.XPath;

Import javax.xml.xpath.XPathConstants;

Import javax.xml.xpath.XPathExpressionException;

Import Javax.xml.xpath.XPathFactory;

public class selectxml{

public void Getselectxml (String query_sentences) throws xpathexpressionexception{

Xpathfactory pathfactory = Xpathfactory.newinstance ();

XPath path = Pathfactory.newxpath ();

The Student.xml file is in the SRC directory.

InputStream in = SelectXML.class.getResourceAsStream ("/student.xml");

InputSource Source = new InputSource (in),//inputsource is closed once used, and re-used again with new.

Specific links to XPath syntax: http://www.w3school.com.cn/xpath/xpath_syntax.asp

String query_sentences= "/students/student/[name= '-Bruce Lee away from ']/age".

Inquire about his age by name "-Bruce Lee".

string evaluate (string Expression,inputsource source);

String age = (Node) path.evaluate (query_sentences, source);

Sysotem.out.println ("The Age of Li Xiao is:" + ages);

}

}

2.4.1 Create a new Datastore class called the Student class: This class is used to encode a Java object into an XML file or to decode an XML file into a Java object

Import Javax.xml.bind.annotation.XmlAttribute;
Import javax.xml.bind.annotation.XmlRootElement;

@XMLRootElement (name= "student")//inject annotations, marking the root element in the class as student.

public class student{

The attribute of the @XmlAttribute (Name= "class")//tag student is class.

Private Clazz;

private String name;

Private String sex;

Private String age;

Set,get,tostring () Province column.

}

2.4.2 Create a new Datastore class called the Studentlist class: This class is used to encode a Java object into an XML file or to decode an XML file into a Java object

Import java.util.List;

Import javax.xml.bind.annotation.XmlElement;

Import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement (name= "Students")//inject annotations, marking the root element in the class as students.

public class studentlist{

Private list<student> students;

Public list<student> getstudents () {return students; }

@XmlElement (name= "student")//inject annotations, marking the element in the class as student.

public void Setstudents (list<student> students) {this.students = students; }

}

2.4.2 Create a new Selectxml class:

Import Java.io.InputStream;

Import Org.xml.sax.InputSource;

Import Javax.xml.xpath.XPath;

Import javax.xml.xpath.XPathConstants;

Import javax.xml.xpath.XPathExpressionException;

Import Javax.xml.xpath.XPathFactory;

Import Javax.xml.bind.JAXBContext;
Import javax.xml.bind.JAXBException;
Import Javax.xml.bind.Marshaller;
Import Javax.xml.bind.Unmarshaller;

public class selectxml{

Public NodeList getselectxml (String query_sentences) throws xpathexpressionexception{

Xpathfactory pathfactory = Xpathfactory.newinstance ();

XPath path = Pathfactory.newxpath ();

InputStream in = SelectXML.class.getResourceAsStream ("/student.xml");

InputSource Source = new InputSource (in);

String query_sentences = "/students/student"

String query_sentences = "/students/student[@class =" 1301 "]"

Object Evaluate (String expression,inputsource source,return retruntype);

Queries all students for all information and returns a collection.

NodeList Student_node = (NodeList) path.evaluate (query_sentences, Source,xpathconstants.nodeset);

Queries all information about a student and returns an element.

Node Student_node = (node) path.evaluate (Query_sentences, Source,xpathconstants.node);

return student_node;

}

Use the Jaxbcontext->unmarshaller () method to decode the student.xml.

Specific Link: http://docs.oracle.com/javase/8/docs/api/javax/xml/bind/Unmarshaller.html

Public list<student> Getunmarshallerjava (NodeList NodeList) throws jaxbexception{

Creates a decoder.

Jaxbcontext JC = jaxbcontext.newinstance (Student.class);

Unmarshaller u = Jc.createunmarshaller ();

list<student> list = new linkedlist<> ();

for (int i = 0;i<nodelist.getlength (); i++) {

Node node = Nodelist.item (i);

to decode.

Student stu = (Student) u.unmarshal (node);

List.add (Stu);
}
return list;

}

Use the Jaxbcontext->marshaller () method to encode an object in Java.

Specific Link: http://docs.oracle.com/javase/8/docs/api/javax/xml/bind/marshaller.html

public static void Getmarshallerxml (List<student> List) throws Xpathexpressionexception, jaxbexception{
Creating encoders
Jaxbcontext JC = jaxbcontext.newinstance (Studentlist.class);
Marshaller u = Jc.createmarshaller ();
Studentliststu = new Studentlist ();
Stu.setstudents (list);
Executes the encoding to create an XML file on the hard disk.
U.marshal (Stu, New File ("D:" +file.separator+ "Student.xml"));
}

}

Java uses XPath to query elements in XML