Best method to parse various custom XML documents in Java

Basically, you have two main XML parsing methods in Java :

• SAX, where you use an handler to only grab what you want in your XML and ditch the rest
• DOM, which parses your file all along, and allows you to grab all elements in a more tree-like fashion.

Another very useful XML parsing method, albeit a little more recent than these ones, and included in the JRE only since Java6, is StAX. StAX was conceived as a medial method between the tree-based of DOM and event-based approach of SAX. It is quite similar to SAX in the fact that parsing very large documents is easy, but in this case the application "pulls" info from the parser, instead of the parsing "pushing" events to the application. You can find more explanation on this subject here.

So, depending on what you want to achieve, you can use one of these approaches.

You will want to use org.xml.sax.XMLReader (http://docs.oracle.com/javase/7/docs/api/org/xml/sax/XMLReader.html).

If you only need to parse then I would recommend using XPath library. Here is a nice reference: http://www.ibm.com/developerworks/library/x-javaxpathapi.html

But you may want to consider turning XMLs to objects and then the sky is the limit. For that you may use XStream, this is a great library which i use alot

Use the dom4j library

First read the document

import java.net.URL;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.io.SAXReader;

public class Foo {

    public Document parse(URL url) throws DocumentException {
        SAXReader reader = new SAXReader();
        Document document = reader.read(url);
        return document;
    }
}

Then use XPATH to get to the values you need

public void get_author(Document document) {
    Node node = document.selectSingleNode( "//AppealRequestProcessRequest/author" );
    String author = node.getText();
    return author;
}

Below is the code of extracting some value value using vtd-xml.

import com.ximpleware.*;

public class extractValue{
    public static void  main(String s[]) throws VTDException, IOException{
        VTDGen vg = new VTDGen();
        if (!vg.parseFile("input.xml", false));
        VTDNav vn = vg.getNav();
        AutoPilot ap = new AutoPilot(vn);
        ap.selectXPath("/aa/bb[name='k1']/value");
        int i=0;
        while ((i=ap.evalXPath())!=-1){
            System.out.println(" value ===>"+vn.toString(i));
        }   
    }
}