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Gerrie van Wyk
Gerrie van Wyk

Reputation: 697

Simple way to extract data from XML with Java

What would be the simplest way to extract data from XML in Java? The XML data is always in the form:

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<groups>GROUPNAME</groups>

and all I want to do is capture the groupname in a string. I've tried using a regular expression, but I'm struggleing to write the pattern code:

String xmlline = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<groups>XWiki.G_SW_DEV</groups>";
String pattern = "";
Pattern r = Pattern.compile(pattern);
Matcher m = r.matcher(xmlline);
if(m.find()){
    ....                     
}

As described in: http://www.tutorialspoint.com/java/java_regular_expressions.htm

Any advice on the pattern code or is there a better way to extract the XML data?

Upvotes: 3

Views: 10163

Answers (3)

Christopher
Christopher

Reputation: 704

In the Java ecosystem exist three different xml-parser approaches. Two of them are stream-based, working with events. The third uses a tree-model (DOM --> Document Object Model) of the document. The stream models are suitable for large documents, whereas the DOM parser are usually considered easier/nicer to program.

Stream/Event:

  • SAX (Simple API for XML) --> you can implement a DocumentHandler that can react to certain events. "Push"-Parser, as it "pushes" events to your Handler.
  • StAX (Stream API for XML) --> "Pull"-Parser, you have to fetch the next event from the parser and can react to it.

See also: this question

DOM:

Take a look at the Oracle Tutorial

Upvotes: 0

Murali sundaram
Murali sundaram

Reputation: 26

Use JAXB marshalling

Example: If you want to read a customer.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer id="100">
    <age>29</age>
    <name>Martin</name>
</customer>

Step 1: Map the xml to class file

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Customer {

String name;
int age;
int id;

public String getName() {
    return name;
}

@XmlElement
public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

@XmlElement
public void setAge(int age) {
    this.age = age;
}

public int getId() {
    return id;
}

@XmlAttribute
public void setId(int id) {
    this.id = id;
}

}

Step 2: Write a reader class


import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;

public class ReadXml {

    public static void main(String[] args) throws JAXBException {
        File file = new File("D:\\customer.xml");
        JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class);

        Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
        Customer customer = (Customer) jaxbUnmarshaller.unmarshal(file);

        System.out.println("Name :" + customer.getName());
        System.out.println("Age :" + customer.getAge());
        System.out.println("Id :" + customer.getId());

}

}


output:

Name :Martin
Age :29
Id :100

Upvotes: 0

guillaume girod-vitouchkina
guillaume girod-vitouchkina

Reputation: 3079

Classical advice: dont use regex. It seems easy at begining, but it's not so easy.

and there are many classical libraries for XML which do it well !

see this: Java:XML Parser

and then, you only need to do this to retrieve elements:

doc.getElementsByTagName("groups")

getElementsByTagName

and, something like that

doc.getElementsByTagName("method").item(0).getTextContent()

Upvotes: 2

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