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.

How to read XML child node values by using a loop in java

Here is my xml code...
<flow>
<TaskID>100</TaskID>
<TaskID>101</TaskID>
<TaskID>102</TaskID>
<TaskID>103</TaskID>
</flow>
I want to know how to get taskID values in a for loop in java. Please help me...

DOM parser solution, fairly simple, no extra libraries required.
public static void main(String[] args) throws SAXException, IOException,
ParserConfigurationException {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
String input = "<outer>";
input += "<otherstuff><TaskID>123</TaskID></otherstuff>";
input += "<flow>";
input += "<TaskID>100</TaskID>";
input += "<TaskID>101</TaskID>";
input += "<TaskID>102</TaskID>";
input += "<TaskID>103</TaskID>";
input += "</flow>";
input += "</outer>";
Document document = builder.parse(new InputSource(new StringReader(
input)));
NodeList flowList = document.getElementsByTagName("flow");
for (int i = 0; i < flowList.getLength(); i++) {
NodeList childList = flowList.item(i).getChildNodes();
for (int j = 0; j < childList.getLength(); j++) {
Node childNode = childList.item(j);
if ("TaskID".equals(childNode.getNodeName())) {
System.out.println(childList.item(j).getTextContent()
.trim());
}
}
}
}
You'd need to use a FileReader instead if your input came from a file.
Document document = builder.parse(new InputSource(new FileReader(
new File("foo.xml"))));
An alternative to getElementsByTagName() is XPath, a query language for XML, this is particularly useful if you have complicated set of conditions to match.
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile("//flow/TaskID/text()");
Object result = expr.evaluate(document, XPathConstants.NODESET);
NodeList nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
System.out.println(nodes.item(i).getTextContent());
}
If your XML file is large, like 100s of MB / GB or you're on a low memory platform then consider a SAX parser.
String input = "<flow><TaskID>100</TaskID><TaskID>101</TaskID><TaskID>102</TaskID><TaskID>103</TaskID></flow>";
SAXParser sax = SAXParserFactory.newInstance().newSAXParser();
DefaultHandler handler = new DefaultHandler() {
private StringBuilder buffer = new StringBuilder();
#Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
if ("TaskID".equals(qName)) {
System.out.println(buffer);
buffer = new StringBuilder();
}
}
#Override
public void characters(char[] ch, int start, int length)
throws SAXException {
buffer.append(ch, start, length);
}
#Override
public void startElement(String uri, String localName,
String qName, Attributes attributes) throws SAXException {
buffer = new StringBuilder();
}
};
sax.parse(new InputSource(new StringReader(input)), handler);

Here's an example using JDOM, which provides a more pleasant API over existing Java XML parsers:
import java.io.File;
import org.jdom2.*;
import org.jdom2.input.*;
public class Test {
// TODO: More appropriate exception handling :)
public static void main (String[] args) throws Exception {
SAXBuilder builder = new SAXBuilder();
Document doc = builder.build(new File("test.xml"));
Element root = doc.getRootElement();
for (Element element : root.getChildren("TaskID")) {
System.out.println(element.getText());
}
}
}
Of course, this assumes that the XML document is small enough to be loaded into memory.
(Obviously you can use the built-in libraries too, and if you're not doing much XML work then that would be fine - I just find them a bit primitive if you're doing any significant amount of work.)

With xpath Here is more information:
http://www.vogella.com/articles/JavaXML/article.html

I personally use JDOM library for all my XML manipulation.. Below is how I would do it;
String xml = "<flow> " +
"<TaskID>100</TaskID>" +
"<TaskID>101</TaskID>" +
"<TaskID>102</TaskID>" +
"<TaskID>103</TaskID>" +
"</flow>";
org.jdom.Document doc = new SAXBuilder().build(new StringReader(xml));
org.jdom.Element rootElement = doc.getRootElement();
List<Element> eles = rootElement.getChildren("TaskID");
for(Element el : eles)
System.out.println(el.getName()+" : "+el.getValue());
You can get it's documentation here: http://www.jdom.org/

Read Xml Children with SAX
<?xml version="1.0"?>
<Patriarch>
<name>Bill</name>
<wife>
<name>Vi</name>
</wife>
<son>
<name>Bill</name>
</son>
<daughter>
<name>Jeri</name>
<husband>
<name>Mark</name>
</husband>
<son>
<name>Greg</name>
</son>
<son>
<name>Tim</name>
</son>
<son>
<name>Mark</name>
</son>
<son>
<name>Josh</name>
<wife>
<name>Kristine</name>
</wife>
<son>
<name>Blake</name>
</son>
<daughter>
<name>Liah</name>
</daughter>
</son>
</daughter>
</Patriarch>
And Java code:
public class ParseXmlSAX {
public static void main(String[] args) {
new ParseXmlSAX("file.xml");
}
public ParseXmlSAX(final String file) {
try {
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
DefaultHandler handler = new DefaultHandler() {
String key = null;
public void startElement(String uri, String localName, String qName, Attributes attributes)
throws SAXException {
if (key == null)
key = "|";
else
key += qName + "|";
}
public void endElement(String uri, String localName, String qName) throws SAXException {
if (!key.equals("|"))
key = key.substring(0, key.lastIndexOf(qName));
}
public void characters(char ch[], int start, int length) throws SAXException {
String conteudo = new String(ch, start, length).trim();
if (!conteudo.isEmpty()) {
System.out.println(key + " = " + conteudo);
}
}
};
saxParser.parse(this.getClass().getResourceAsStream(file), handler);
} catch (Exception e) {
e.printStackTrace();
}
}
}

public class Modifier {
public void modifyXML() {
String strSrcFile = "E:\\projects\\input\\sample.xml";
String strOutputFile = "E:\\projects\\output\\sample.xml";
try {
DocumentBuilderFactory docFactory = DocumentBuilderFactory
.newInstance();
DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
Document doc = docBuilder.parse(strSrcFile);
Node company = doc.getFirstChild();
System.out.println(company.hasChildNodes());
NodeList nl = company.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
// System.out.println("inner node::"+node.getNodeName());
if (node.hasChildNodes()) {
System.out.println("outer node::" + node.getNodeName());
readChildNodes(node);
} else {
}
}
TransformerFactory transformerFactory = TransformerFactory
.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(new File(strOutputFile));
transformer.transform(source, result);
} catch (Exception ee) {
ee.printStackTrace();
}
// Get the root element
}
public void readChildNodes(Node node)
{
NodeList nl = node.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node innernode = nl.item(i);
//System.out.println("mediam stage node::"+innernode.getNodeName());
if (innernode.hasChildNodes()) {
System.out.println("inner node::"+innernode.getNodeName());
readChildNodes(innernode);
}
else{
System.out.println("node dont have childs node::"+innernode.getNodeName());
}
}
}
public void replaceGraphicCode(Node innernode) {
NamedNodeMap attr = innernode.getAttributes();
Node nodeAttr = attr.getNamedItem("id");
String IDvalue = nodeAttr.getTextContent();
// nodeAttr.setTextContent("2");
}
public void replaceOriginator(Node innernode) {
NamedNodeMap attr = innernode.getAttributes();
Node nodeAttr = attr.getNamedItem("enterpriseCode");
}
public static void main(String[] args) {
Modifier objModifier = new Modifier();
objModifier.modifyXML();
}
}

XQUERY JAVA not working

I'm getting some attributes from a complex XML file:
<rsp>
<csl d='10775.916760613756' id='2003' nam='AUTOS TEZIUTLÁN, S.A. DE C.V.'
adr='KM. 1 CARR. TEZIUTLÁN-TLAPACOYAN' tel='231312-12-05'
lat='19.826765' lon='-97.347906' />
<csl d='10789.680721293766' id='2019' nam='AUTOMOVILÍSTICA DE TEHUACAN, S.A. DE C.V.'
adr='BLVD. ADOLFO LOPEZ MATEOS NO. 3623' tel='238382-44-33'
lat='18.467281' lon='-97.417901' />
<csl d='10848.586325071066' id='2013' nam='AUTOMOTRIZ DE LA SIERRA, S.A. DE C.V.'
adr='AUSENCIO T. JIMÉNEZ No. 1' tel='776762-05-42'
lat='20.174386' lon='-98.06125' />
<csl d='10866.815936520663' id='2028' nam='MOTORES ALEMANES RIVERA S.A. DE C.V.'
adr='CALZADA IGNACIO ZARAGOZA NO. 180' tel='222286-02-02'
lat='19.064258' lon='-98.179042' />
<csl d='10867.374198658401' id='2012' nam='ARMENTA AUTOMOTRIZ, S.A. DE C.V.'
adr='24 NORTE No. 214' tel='222235-87-68'
lat='19.038912' lon='-98.183101' />
</rsp>
But my XQUERY only gives me the first attribute and only that using this class:
public class XMLParser {
private String[] resultTable;
public XMLParser(){}
public String[] stringToXML(String xmlString) {
try{
DocumentBuilderFactory dBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dBuilderFactory.newDocumentBuilder();
InputSource iSource = new InputSource();
iSource.setCharacterStream(new StringReader(xmlString));
Document doc = dBuilder.parse(iSource);
NodeList nList = doc.getElementsByTagName("tpr");
resultTable = new String [nList.getLength()];
for (int i=0; i<nList.getLength(); i++){
Element e = (Element)nList.item(i);
NodeList pCode = e.getElementsByTagName("tpr");
Element line = (Element)pCode.item(0);
resultTable[i] = getCharacterDataFromElement(line);
}
}
catch(Exception e) {
e.printStackTrace();
}
return resultTable;
}
public static String getCharacterDataFromElement(Element e) {
Node child = e.getFirstChild();
if (child instanceof CharacterData) {
CharacterData cData = (CharacterData) child;
return cData.getData();
}
return "null";
}
public static String getParamByXPath(String xmlString, String expression) {
String ret = "";
XPath xpath = XPathFactory.newInstance().newXPath();
try{
DocumentBuilderFactory dBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dBuilderFactory.newDocumentBuilder();
InputSource iSource = new InputSource();
iSource.setCharacterStream(new StringReader(xmlString));
Document doc = dBuilder.parse(iSource);
XPathExpression exp = xpath.compile(expression);
Object result = exp.evaluate(doc);
if (result instanceof String) ret = (String)result;
else if (result instanceof Boolean) ret = result.toString();
else if (result instanceof Double) ret = result.toString();
else if (result instanceof NodeList) {
NodeList list = (NodeList) result;
Node node = list.item(0);
Log.d("LIST", Integer.toString(list.getLength()));
ret = node.getTextContent();
}
}catch(Exception e) {
e.printStackTrace();
}
return ret;
}
I'm invoking the method with this line:
String loc1 = XMLParser.getParamByXPath(service, "//#d");
I have been using other Querys, but the result is always the first element... what could I be missing?

The //#d XPath will return a list of all #d attribute nodes in your document.
Your Java code:
else if (result instanceof NodeList) {
NodeList list = (NodeList) result;
Node node = list.item(0); // <-- THIS ONE HERE
Log.d("LIST", Integer.toString(list.getLength()));
ret = node.getTextContent();
}
will then take the first one (list.item(0)) and that's what you're getting.
It looks like your "issue" is with the Java logic, not the XPath.

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.