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Looking for a specific child in XML using java

I've been looking for the past few hours, and I can't find how to do it.
My XML file:
<list>
<Company id="01">
<Name>Atari</Name>
<Founded>1972</Founded>
<Consoles>
2600
5200
7800
</Consoles>
</Company>
<Company id="02">
<Name>Sega</Name>
<Founded>1960</Founded>
<Consoles>
Master System
Megadrive
Saturn
</Consoles>
</Company>
</list>
Basically, I want the code to find not only the name in one company block, but the name in any company block I wish, and be able to show it to other classes. So far, I've been able to show either or, but only by changing the code directly and not on the fly. The code I'm using:
private static String getTextValue(String def, Element doc, String tag) {
String value = def;
NodeList nl;
nl = doc.getElementsByTagName(tag);
if (nl.getLength() > 0 && nl.item(0).hasChildNodes()) {
value = nl.item(0).getFirstChild().getNodeValue();
}
if(value==null) value = " ";
return value;
}
public static boolean readXML(String xml) {
rolev = new ArrayList<String>();
Document dom;
// Make an instance of the DocumentBuilderFactory
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
// use the factory to take an instance of the document builder
DocumentBuilder db = dbf.newDocumentBuilder();
// parse using the builder to get the DOM mapping of the
// XML file
dom = db.parse(xml);
Element doc = dom.getDocumentElement();
role1 = getTextValue(role1, doc, "Name");
if (getRole1() != null) {
if (!getRole1().isEmpty())
rolev.add(getRole1());
}
role2 = getTextValue(role2, doc, "Founded");
if (role2 != null) {
if (!role2.isEmpty())
rolev.add(role2);
}
role3 = getTextValue(role3, doc, "Consoles");
if (role3 != null) {
if (!role3.isEmpty())
rolev.add(role3);
}
role4 = getTextValue(role4, doc, "Name");
if ( role4 != null) {
if (!role4.isEmpty())
rolev.add(role4);
}
return true;
} catch (ParserConfigurationException pce) {
System.out.println(pce.getMessage());
} catch (SAXException se) {
System.out.println(se.getMessage());
} catch (IOException ioe) {
System.err.println(ioe.getMessage());
}
return false;
}
I used a lot of different methods, some searched up and some made on my own, but this one is the closest I can get to working for what I need. I need to be able to have the place it's looking change on the fly though.

You can use xpath to read XML. See Parsing XML with XPath in Java and/or How to read XML using XPath in Java
In your case, if you wanted to get all of the company names the set path you would use (basically the tag filter) would be "//list/Company/Name/text()"
The rest of the code can basically be copied from the questions I posted. Only your set (filter) would be different.

Storing an XML resource as an object rather than a file

Please turn your phasers to "noob".
As a part of my Java Servlet, I make a call to a REST resource and accept the text file returned, as below:
// check to see if the file really exists (i.e. a session is in
// progress) or we need to create one
// this should save constantly hitting the server for a new file for
// every transaction.
if (fXmlFile.exists()) {
} else {
File collectionTree = new File(bscConnector.GetCollection());
PrintWriter xmlfile = new PrintWriter(directoryName + "/outputString.xml");
xmlfile.println(collectionTree);
xmlfile.close();
}
From there I run a search and replace on it to make it valid XML file so that I can actually run xpath queries against it:
SearchAndReplace sAndR = new SearchAndReplace();
// Swap the slashes so we can actually
// query the freakin' document.
sAndR.readFiles(fXmlFile, "\\", "/");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder;
Document doc = null;
try {
dBuilder = dbFactory.newDocumentBuilder();
doc = dBuilder.parse(fXmlFile);
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// optional, but recommended
// read this -
// http://stackoverflow.com/questions/13786607/normalization-in-dom-parsing-with-java-how-does-it-work
doc.getDocumentElement().normalize();
// Create an instance of an xpath object
XPath xPath = XPathFactory.newInstance().newXPath();
And then I go to town on it with various xpath queries that create the interface, yadda yadda.
My question is this; while this approach works, it seems freakishly weird to be creating and querying an actual file on the server rather than doing all this in a session object, but I can't find the correct way of doing this; what object/set of objects should I be using instead of this serialize-to-disk-and-read approach?
Thanks.

This question turned out to be so simple I'm considering deleting it just to prevent polluting stackoverflow; it was a basic misunderstanding of what Java could do with a String. I replaced all the file manipulation stuff with:
String fXmlFile = null;
if (fXmlFile != null) {} else {
File collectionTree = new File(bscConnector.GetCollection());
fXmlFile = collectionTree.toString();
fXmlFile = fXmlFile.replace("\\", "/");
}
and other than that left my code unchanged. All works, much faster too since it's not serializing and deserializing a large text file any more.
I'm going to move the initialization of the fXmlFile out of the JSP and into the servlet, define it as a session object, and pass it in as a part of the request because right now I'm having to declare it as null right before I test to see if it's null, which seems self-defeating. Other than that, it's all good.
Thanks eldjon.

Xpath approach in case of large files

The class you're gonna see right now is the classic approach to parse an XML document via XPath in Java:
public class Main {
private Document createXMLDocument(String fileName) throws Exception {
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse(fileName);
return doc;
}
private NodeList readXMLNodes(Document doc, String xpathExpression) throws Exception {
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile(xpathExpression);
Object result = expr.evaluate(doc, XPathConstants.NODESET);
NodeList nodes = (NodeList) result;
return nodes;
}
public static void main(String[] args) throws Exception {
Main m = new Main();
Document doc = m.createXMLDocument("tv.xml");
NodeList nodes = m.readXMLNodes(doc, "//serie/eason/#id");
int n = nodes.getLength();
Map<Integer, List<String>> series = new HashMap<Integer, List<String>>();
for (int i = 1; i <= n; i++) {
nodes = m.readXMLNodes(doc, "//serie/eason[#id='" + i + "']/episode/text()");
List<String> episodes = new ArrayList<String>();
for (int j = 0; j < nodes.getLength(); j++) {
episodes.add(nodes.item(j).getNodeValue());
}
series.put(i, episodes);
}
for (Map.Entry<Integer, List<String>> entry : series.entrySet()) {
System.out.println("Season: " + entry.getKey());
for (String ep : entry.getValue()) {
System.out.println("Episodio: " + ep);
}
System.out.println("+------------------------------------+");
}
}
}
In there I find some methods to be worrying in case of a huge xml file. Like the use of
Document doc = builder.parse(fileName);
return doc;
or
Object result = expr.evaluate(doc, XPathConstants.NODESET);
NodeList nodes = (NodeList) result;
return nodes;
I'm worried because the xml document I need to handle is created by the customer and inside you can basically have an indefinite number of records describing emails and their contents (every user has its own personal email, so lots of html in there). I know it's not the smartest approach but it's one of the possibilities and it was already up and running before I arrived here.
My question is: how can I parse and evaluate huge xml files using xpath?

You could use the StAX parser. It will take less memory than the DOM options. A good introduction to StAX is at http://tutorials.jenkov.com/java-xml/stax.html

First of all, XPath doesn't parse XML. Your createXMLDocument() method does that, producing as output a tree representation of the parsed XML. The XPath is then used to search the tree representation.
What you are really looking for is something that searches the XML on the fly, while it is being parsed.
One way to do this is with an XQuery system that implements "document projection" (for example, Saxon-EE). This will analyze your query to see what parts of the document are needed, and when you parse your document, it will build a tree containing only those parts of the document that are actually needed.
If the query is as simple as the one in your example, however, then it isn't too hard to code it as a SAX application, where events such as startElement and endElement are notified by the XML parser to the application, without building a tree in memory.

How can I automate the XML Parsing using JDOM

I have to parse an XML file using JDOM and get some infos from all his elements.
<?xml version="1.0" encoding="UTF-8"?>
<root>
<element1>something</element1>
<element2>
<subelement21>moo</subelement21>
<subelement22>
<subelement221>toto</subelement221>
<subelement222>tata</subelement222>
</subelement22>
</element2>
</root>
So, for the element1 it's easy. But for the element2 I have to go through his children and if the children has children go through them too and so on.
public static void getInfos(Vector<String> files) {
Document document = null;
Element root = null;
SAXBuilder sxb = new SAXBuilder();
for (int i =0 ; i< files.size() ; i++)
{
System.out.println("n°" + i + " : " + files.elementAt(i));
try
{
document = sxb.build(files.elementAt(i));
root = document.getRootElement();
List<?> listElements = root.getChildren();
Iterator<?> it = listElements.iterator();
while(it.hasNext())
{
Element courant = (Element)it.next();
System.out.println(courant.getName());
if(courant.getChildren().size() > 0)
{
// here is the problem -> the element has a children
}
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
What do you suggest in this case, like a recursive call or something else so I can use the same function.
Thanks.

I would use SAX. I'd keep a stack in the contenthandler that tracked what my current path was in the document, and keep a buffer that my characters method appended to. In endElement I'd get the content from the buffer and clear it out, then use the current path to decide what to do with it.
(this is assuming this document has no mixed-content.)
Here's a link to an article on using SAX to process complex XML documents, it expands on what I briefly described into an approach that handles recursive data structures. (It also has a predecessor article that is an introduction to SAX.)

You could consider using XPath to get the exact elements you want. The example here uses namespaces but the basic idea holds.

How do you traverse and store XML in Blackberry Java app?

I'm having a problem accessing the contents of an XML document.
My goal is this:
Take an XML source and parse it into a fair equivalent of an associative array, then store it as a persistable object.
the xml is pretty simple:
<root>
<element>
<category_id>1</category_id>
<name>Cars</name>
</element>
<element>
<category_id>2</category_id>
<name>Boats</name>
</element>
</root>
Basic java class below. I'm pretty much just calling save(xml) after http response above. Yes, the xml is properly formatted.
import java.io.IOException;
import java.util.Hashtable;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import java.util.Vector;
import net.rim.device.api.system.PersistentObject;
import net.rim.device.api.system.PersistentStore;
import net.rim.device.api.xml.parsers.DocumentBuilder;
import net.rim.device.api.xml.parsers.DocumentBuilderFactory;
public class database{
private static PersistentObject storeVenue;
static final long key = 0x2ba5f8081f7ef332L;
public Hashtable hashtable;
public Vector venue_list;
String _node,_element;
public database()
{
storeVenue = PersistentStore.getPersistentObject(key);
}
public void save(Document xml)
{
venue_list = new Vector();
storeVenue.setContents(venue_list);
Hashtable categories = new Hashtable();
try{
DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory. newInstance();
DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
docBuilder.isValidating();
xml.getDocumentElement ().normalize ();
NodeList list=xml.getElementsByTagName("*");
_node=new String();
_element = new String();
for (int i=0;i<list.getLength();i++){
Node value=list.item(i).getChildNodes().item(0);
_node=list.item(i).getNodeName();
_element=value.getNodeValue();
categories.put(_element, _node);
}
}
catch (Exception e){
System.out.println(e.toString());
}
venue_list.addElement(categories);
storeVenue.commit();
}
The code above is the work in progress, and is most likely heavily flawed. However, I have been at this for days now. I can never seem to get all child nodes, or the name / value pair.
When I print out the vector as a string, I usually end up with results like this:
[{ = root, = element}]
and that's it. No "category_id", no "name"
Ideally, I would end up with something like
[{1 = cars, 2 = boats}]
Any help is appreciated.
Thanks

Here's a fixed version of your program. Changes that I made are as follows:
I removed the DocBuilder-stuff from the save() method. These calls are needed to construct a new Document. Once you have such an object (and you do since it is passed in as an argument) you don't need the DocumentBuilder anymore. A proper use of DocumentBuilder is illustrated in the main method, below.
_node,_element need not be fields. They get new values with each pass through the loop inside save so I made them local variables. In addition I changed their names to category and name to reflect their association with the elements in the XML document.
There's never a need to create a new String object by using new String(). A simple "" in enough (see the initialization of the category and name variables).
Instead of looping over everything (via "*") the loop now iterates over element elements. Then there is a an inner loop that iterates over the children of each element, namely: its category_id and name elements.
In each pass of the inner we set either the category or the name variable depending on the name of the node at hand.
The actual value that is set to these variables is obtained by via node.getTextContent() which returns the stuff between the node's enclosing tags.
class database:
public class database {
private static PersistentObject storeVenue;
static final long key = 0x2ba5f8081f7ef332L;
public Hashtable hashtable;
public Vector venue_list;
public database() {
storeVenue = PersistentStore.getPersistentObject(key);
}
public void save(Document xml) {
venue_list = new Vector();
storeVenue.setContents(venue_list);
Hashtable categories = new Hashtable();
try {
xml.getDocumentElement().normalize();
NodeList list = xml.getElementsByTagName("element");
for (int i = 0; i < list.getLength(); i++) {
String category = "";
String name = "";
NodeList children = list.item(i).getChildNodes();
for(int j = 0; j < children.getLength(); ++j)
{
Node n = children.item(j);
if("category_id".equals(n.getNodeName()))
category = n.getTextContent();
else if("name".equals(n.getNodeName()))
name = n.getTextContent();
}
categories.put(category, name);
System.out.println("category=" + category + "; name=" + name);
}
} catch (Exception e) {
System.out.println(e.toString());
}
venue_list.addElement(categories);
storeVenue.commit();
}
}
Here's a main method:
public static void main(String[] args) throws Exception {
DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory
.newInstance();
DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
docBuilder.isValidating();
Document xml = docBuilder.parse(new File("input.xml"));
database db = new database();
db.save(xml);
}

Thank you so much. With only slight modification I was able to do exactly what I was looking for.
Here are the modifications I had to do:
Even though I am building in 1.5, getTextContent was not available. I had to use category = n.getFirstChild().getNodeValue(); to obtain the value of each node. Though there may have been a simple solution like updating my build settings, I am not familiar enough with BB requirements to know when it is safe to stray from the default recommended build settings.
In the main, I had to alter this line:
Document xml = docBuilder.parse(new File("input.xml"));
so that it was reading from an InputStream delivered from my web server, and not necessarily a local file - even though I wonder if storing the xml local would be more efficient than storing a vector full of hash tables.
...
InputStream responseData = connection.openInputStream();
Document xmlParsed = docBuilder.parse(result);
Obviously I skipped over the HTTP connection portion for the sake of keeping this readable.
Your help has saved me a full weekend of blind debugging. Thank you very much! Hopefully this post will help someone else as well.

//res/xml/input.xml
private static String _xmlFileName = "/xml/input.xml";
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
InputStream inputStream = getClass().getResourceAsStream( _xmlFileName );
Document document = builder.parse( inputStream );