Develop Reference

Parsing XML in a method returns nothing

try {
DocumentBuilder builder=factory.newDocumentBuilder();
Document doc = builder.parse("15122021.xml");
NodeList currencyList= doc.getElementsByTagName("Currency");
for(int i=0;i<currencyList.getLength();i++){
Node p = currencyList.item(i);
if(p.getNodeType()==Node.ELEMENT_NODE){
Element mainTag = (Element) p;
NodeList currencySellPriceList= mainTag.getElementsByTagName("ForexSelling");
NodeList currencyBuyPriceList = mainTag.getElementsByTagName("ForexBuying");
NodeList currencyNameList2= mainTag.getElementsByTagName("CurrencyName");
for(int j=0;j<currencyNameList2.getLength();j++){
Node c=currencyNameList2.item(j);
Node cbp=currencyBuyPriceList.item(j);
Node csp=currencySellPriceList.item(j);
if(c.getNodeType()==Node.ELEMENT_NODE && cbp.getNodeType()==Node.ELEMENT_NODE && csp.getNodeType()==Node.ELEMENT_NODE){
System.out.println("Currency name: "+c.getTextContent());
System.out.println("Buy price: "+cbp.getTextContent());
System.out.println("Sell price: "+csp.getTextContent());
}
}
}
}
} catch (ParserConfigurationException e) {
System.out.println(e.getMessage());
} catch (IOException e) {
System.out.println(e.getMessage());
} catch (SAXException e) {
System.out.println(e.getMessage());
}
I am trying to parse XML file like this in main method and it works.But when i try to take this code block to another method like this
public class XMLScraperBuilder {
public NodeList getBuyPrices() throws IOException, SAXException, ParserConfigurationException {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
NodeList currencySellPriceList=null;
DocumentBuilder builder=factory.newDocumentBuilder();
Document doc = builder.parse("15122021.xml");
NodeList currencyList= doc.getElementsByTagName("Currency");
for(int i=0;i<currencyList.getLength();i++){
Node currency = currencyList.item(i);
if(currency.getNodeType()==Node.ELEMENT_NODE){
Element mainTag = (Element) currency;
currencySellPriceList= mainTag.getElementsByTagName("ForexSelling");
for(int j=0;j<currencySellPriceList.getLength();j++){
Node c = currencySellPriceList.item(j);
}
}}
return currencySellPriceList;
}}
It returns nothing when i try to print the NodeList with a for loop in my main method(after creating an object from XMLScraperBuilder).Any ideas?

nullpointerexception while trying to read from xml file with dom parser

I am trying to read from xml file but I get a null pointer exception.
this is the xml file:
<war>
<missileLaunchers>
<launcher id="L101" isHidden="false">
<missile id="M1" destination="Sderot" launchTime="2" flyTime="12" damage="1500"/>
<missile id="M2" destination="Beer-Sheva" launchTime="5" flyTime="7" damage="2000"/>
</launcher>
<launcher id="L102" isHidden="true">
<missile id="M3" destination="Ofakim" launchTime="4" flyTime="3" damage="5000"/>
<missile id="M4" destination="Beer-Sheva" launchTime="9" flyTime="7" damage="1000"/>
</launcher>
</missileLaunchers>
<missileDestructors >
<destructor id="D201">
<destructdMissile id="M1" destructAfterLaunch="4"/>
<destructdMissile id="M3" destructAfterLaunch="7" />
<destructdMissile id="M4" destructAfterLaunch="2"/>
</destructor>
<destructor id="D202">
<destructdMissile id="M2" destructAfterLaunch="3"/>
</destructor>
</missileDestructors>
<missileLauncherDestructors >
<destructor type="plane" >
<destructedLanucher id="L101" destructTime="4"/>
</destructor>
<destructor type="ship">
<destructedLanucher id="L102" destructTime="8" />
<destructedLanucher id="L102" destructTime="12"/>
</destructor>
</missileLauncherDestructors>
</war>
and this is the code:
public class XmlReader
{
File fXmlFile=null;
DocumentBuilderFactory dbFactory=null;
DocumentBuilder dBuilder=null;
Document doc=null;
public XmlReader(String filePath) throws ClassNotFoundException
{
if(filePath!=null)
{
this.fXmlFile = new File(filePath);
dbFactory = DocumentBuilderFactory.newInstance();
try {
dBuilder = dbFactory.newDocumentBuilder();
} catch (ParserConfigurationException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
doc = dBuilder.parse(fXmlFile);
doc.getDocumentElement().normalize();
} catch (SAXException | IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
else System.out.println("Xml file not found");
}
//gets value by tag name
private static String getTagValue(String tag, Element element) {
if(element.hasChildNodes())
{
NodeList nodeList = element.getElementsByTagName(tag).item(0).getChildNodes();
Node node = (Node) nodeList.item(0);
if(node==null)
return null;
return node.getNodeValue();
}
else return element.getNodeValue();
}
//launcher
public List<Launcher> readLauncher() throws Exception
{
List<Launcher> launcherList = new ArrayList<Launcher>();
try
{
NodeList nList = doc.getElementsByTagName("launcher");
for(int i=0;i<nList.getLength();i++)
{launcherList.add(getLauncher(nList.item(i)));}
}
catch (Exception e)
{
e.printStackTrace();
}
return launcherList;
}
//builds the object
private static Launcher getLauncher(Node node)
{
//XMLReaderDOM domReader = new XMLReaderDOM();
Launcher launcher = new Launcher();
if (node.getNodeType() == Node.ELEMENT_NODE)
{
Element element = (Element) node;
// launcher.setIsHidden(Boolean.parseBoolean(getTagValue("isHidden", element)));
// launcher.setId(getTagValue("id", element));
System.out.println("id = "+getTagValue("id", element));
System.out.println("ishidden = "+getTagValue("isHidden", element));
}
return launcher;
}
}
And this is the stack trace:
java.lang.NullPointerException
at XmlReader.getTagValue(XmlReader.java:56)
at XmlReader.getLauncher(XmlReader.java:96)
at XmlReader.readLauncher(XmlReader.java:78)
at Program.main(Program.java:27)
I can not change the format of the xml file.
It seems to fail when it tries to get the actual value of the node's fields or so I assume.
Though I don;t understand the reason...when I check the size of the node list it turns fine it does give me 2.

The problem is below line:
System.out.println("id = " + getTagValue("id", element));
where getTagValue("id", element) is calling
NodeList nodeList = element.getElementsByTagName(tag).item(0).getChildNodes();
Here element.getElementsByTagName("id") will return null
It should be get from attribute
// gets value by tag name
private static String getTagValue(String tag, Element element) {
return element.getAttributeNode(tag).getValue();
}

You are calling getElementsByTagName() in getTagValues, however you are trying to retrieve attributes of the tag. You may need to call getAttribute() instead. For Example:
element.getAttribute(attributeName)
where attributeName is "id" or "isHidden". This will return the value as a String and can be returned directly with no further processing.

Simple XML parse XML to List

I use Simple XML (simple-xml-2.6.2.jar) to parse xml file like:
<?xml version="1.0" encoding="UTF-8" ?>
<orderList>
<order id="1">
<name>NAME1</name>
</order>
<order id="2">
<name>NAME2</name>
</order>
</orderList>
The root Element contains subElements.
I wanna it be ArrayList, How to do it?

Here's a possible solution, hope it helps you:
Annotations of Order class:
#Root(name="order")
public class Order
{
#Attribute(name="id", required=true)
private int id;
#Element(name="name", required=true)
private String name;
public Order(int id, String name)
{
this.id = id;
this.name = name;
}
public Order() { }
// Getter / Setter
}
Example class, containing the list:
#Root(name="elementList")
public class Example
{
#ElementList(required=true, inline=true)
private List<Order> list = new ArrayList<>();
// ...
}
And here's some code for reading your code:
Serializer ser = new Persister();
Example example = ser.read(Example.class, file); // file = your xml file
// 'list' now contains all your Orders

List is an interface, ArrayList is one of its implementation, like:
List<Order> l = new ArrayList<Order>()
So if you have a List , you basically have what you want.

If I've interpreted your question correctly, you want a list of orders. I've not tested this for your setup but this works for me for a similar xml structure (assumes you have a custom class called Order):
List<Order> orders = new ArrayList<Order>();
XMLDOMParser parser = new XMLDOMParser();
AssetManager manager = context.getAssets();
InputStream stream;
try {
stream = manager.open("test.xml"); //need full path to your file here - mine is stored in assets folder
Document doc = parser.getDocument(stream);
}catch(IOException ex){
System.out.printf("Error reading xml file %s\n", ex.getMessage());
}
NodeList nodeList = doc.getElementsByTagName("order");
for (int i = 0; i < nodeList.getLength(); i++) {
Element e = (Element) nodeList.item(i); //each order item
Node order=nodeList.item(i);
subList = order.getFirstChild(); //get the name child node
orders.add(order);
}
//XMLDOMParser Class
public class XMLDOMParser {
//Returns the entire XML document
public Document getDocument(InputStream inputStream) {
Document document = null;
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder db = factory.newDocumentBuilder();
InputSource inputSource = new InputSource(inputStream);
document = db.parse(inputSource);
} catch (ParserConfigurationException e) {
Log.e("Error: ", e.getMessage());
return null;
} catch (SAXException e) {
Log.e("Error: ", e.getMessage());
return null;
} catch (IOException e) {
Log.e("Error: ", e.getMessage());
return null;
}
return document;
}
/*
* I take a XML element and the tag name, look for the tag and get
* the text content i.e for <employee><name>Kumar</name></employee>
* XML snippet if the Element points to employee node and tagName
* is name I will return Kumar. Calls the private method
* getTextNodeValue(node) which returns the text value, say in our
* example Kumar. */
public String getValue(Element item, String name) {
NodeList nodes = item.getElementsByTagName(name);
return this.getTextNodeValue(nodes.item(0));
}
private final String getTextNodeValue(Node node) {
Node child;
if (node != null) {
if (node.hasChildNodes()) {
child = node.getFirstChild();
while(child != null) {
if (child.getNodeType() == Node.TEXT_NODE) {
return child.getNodeValue();
}
child = child.getNextSibling();
}
}
}
return "";
}
}

Xpath can't query tag with namespace

I have xml like below (Google API), but can't get gphoto:id element value. How to do that ? Notice: When i'm using domFactory.setNamespaceAware(true);, /feed/entry xpath stops working.
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
xmlns:gphoto="http://schemas.google.com/photos/2007"
xmlns:media="http://search.yahoo.com/mrss/"
xmlns:openSearch="http://a9.com/-/spec/opensearchrss/1.0/">
<entry>
<title type="text">Test</title>
<author>
<name>username</name>
<uri>https://picasaweb.google.com/113422203255202384532</uri>
</author>
<gphoto:id>57060151229174417</gphoto:id>
</entry>
</feed>
Java
NodeList nodes = (NodeList) path(body, "/feed/entry", XPathConstants.NODESET);
for (int i = 0; i < nodes.getLength(); i++) {
Node n = nodes.item(i);
XPath xpath = XPathFactory.newInstance().newXPath();
// empty :(
System.out.println(
xpath.evaluate("id[namespace-uri()='http://schemas.google.com/photos/2007']",n)
);
// empty too :(
System.out.println(
xpath.evaluate("gphoto:id",n)
);
// ok
System.out.println(
xpath.evaluate("author",n)
);
l.add(new Album("", "", ""));
}
path method
private Object path(String content, String path, QName returnType) {
try {
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(content)));
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile(path);
return expr.evaluate(doc, returnType);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
SOLVED according to #gioele answer path() method is now like below:
private Object path(String content, String path, QName returnType) {
try {
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(content)));
XPath xpath = XPathFactory.newInstance().newXPath();
NamespaceContext nsContext = new NamespaceContext() {
#Override
public Iterator getPrefixes(String namespaceURI) {
return null;
}
#Override
public String getPrefix(String namespaceURI) {
return null;
}
#Override
public String getNamespaceURI(String prefix) {
if ("gphoto".equals(prefix))
return "http://schemas.google.com/photos/2007";
if ("media".equals(prefix))
return "http://search.yahoo.com/mrss/";
if("".equals(prefix))
return "http://www.w3.org/2005/Atom";
throw new IllegalArgumentException(prefix);
}
};
xpath.setNamespaceContext(nsContext);
XPathExpression expr = xpath.compile(path);
return expr.evaluate(doc, returnType);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}

Before compiling your xpath you need to register a NamespaceContext.
Have a look at the code in https://github.com/gioele/xpathapi-jaxp/blob/master/src/main/java/it/svario/xpathapi/jaxp/NodeNamespaceContext.java.
If you want to avoid all these complications, you can use the XPathAPI library:
Map<String, String> nsMap = new HashMap<String, String>();
nsMap.put(XMLConstants.DEFAULT_NS_PREFIX, "http://www.w3.org/2005/Atom");
nsMap.put("gphoto", "http://schemas.google.com/photos/2007");
List<Node> entries = XPathAPI.selectListOfNodes(doc, "/feed/entry", nsMap);
for (Node entry : entries) {
String id = XPathAPI.selectSingleNodeAsString(entry, "gphoto:id", nsMap);
// or, if you prefer a Node
// Node id = XPathAPI.selectSingleNode(entry, "gphoto:id", nsMap);
}
Disclaimer: I am the creator of XPathAPI-JAXP.

A much easier way to deal with the namespace issue is just to redirect the call from the NamespaceContext to the document lookupNamespaceURI() method. This will return "http://search.yahoo.com/mrss/" when called with "media" etc...
xPath.setNamespaceContext(new NamespaceContext() {
#Override
public String getNamespaceURI(String prefix) {
return doc.lookupNamespaceURI(prefix);
}
#Override
public Iterator<?> getPrefixes(String arg0) {
return null;
}
#Override
public String getPrefix(String arg0) {
return null;
}
});

Java DOM XML Parsing

So I have an XML file in the format:
<projectlist>
<project>
<name>test</name>
<type>deploy</type>
<environment>dev</environment>
<server>test01</server>
<server>test02</server>
<server>test03</server>
</project>
</projectlist>
I'm trying to parse this file and build an object that I can populate a JListBox with the names and a radiobutton group with the different servers, however each project consists of a different amount of servers. How do I iterate the nodes/childnodes to build the object with multiple servers. Here is snippets of the code I'm using borrowed from a website and some from me and I'm not very good at coding yet so bear with me please. When I debug it starts to parse & build the object but once it gets to the server names it prints a null pointer exception so I'm doing something totally wrong.
public class XMLParser {
public Project currentProject = new Project();
public void parseXML() throws Exception {
try {
File file = new File("c:\\projectlist.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(file);
doc.getDocumentElement().normalize();
NodeList nList = doc.getElementsByTagName("project");
for (int temp = 0; temp < nList.getLength(); temp++) {
Node nNode = nList.item(temp);
if (nNode.getNodeType() == Node.ELEMENT_NODE) {
Element eElement = (Element) nNode;
currentProject.SetAppName(getTagValue("name", eElement));
currentProject.SetType(getTagValue("type", eElement));
currentProject.SetEnvironment(getTagValue("environment", eElement));
currentProject.SetServerName(getTagValue("server", eElement));
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
private static String getTagValue(String sTag, Element eElement) {
NodeList nlList = eElement.getElementsByTagName(sTag).item(0).getChildNodes();
Node nValue = (Node) nlList.item(0);
return nValue.getNodeValue();
}
public final class Project {
protected String AppName = null;
protected String Type = null;
protected List<String> ServerNames = null;
protected String Environment = null;
public void SetAppName(String AppName) {
this.AppName = AppName;
}
public void SetType(String DeployType) {
this.Type = DeployType;
}
public void SetServerName(String ServerName) {
this.ServerNames.add(ServerName);
}
public void SetEnvironment(String Environment) {
this.Environment = Environment;
}
public String getAppName() {
return AppName;
}
public String getType() {
return Type;
}
public List<String> getServerName() {
return ServerNames;
}
public String getEnvironment() {
return Environment;
}
}

Your exception is being caused because you didn't initialize ServerNames in your Project class. Try to initialize it as follows and rerun:
final protected List<String> ServerNames = new ArrayList<String>();

If your xml was created using an xsd schema, you could instead use JAXB to create classes for it, using the xjc tool. That should make your life a bit easier.