URL: http://ws.audioscrobbler.com/2.0/?method=chart.gethypedtracks&api_key=1732077d6772048ccc671c754061cb18&limit=10
From the above url I need to somehow remove the Artist name and the track name from the XML file produced from each Song given but I have no Idea how to work with an XML file structured in this way ??
Any help or pointers would be very much appreciated !
Thanks,
Ross
Here's a fully working class that loads the URL you have indicated and parses the Track and artist names.
Basically it reads the xml into a Document, and runs 2 xpath queries in loops to get the data you want.
The document itself is simple xml, if you reformat it, it looks like:
<?xml version="1.0" encoding="utf-8"?>
<lfm status="ok">
<tracks page="1" perPage="10" totalPages="50" total="500">
<track>
<name>Hysterical</name>
<duration>231</duration>
<percentagechange>3626</percentagechange>
<mbid/>
<url>http://www.last.fm/music/Clap+Your+Hands+Say+Yeah/_/Hysterical</url>
<streamable fulltrack="0">0</streamable>
<artist>
<name>Clap Your Hands Say Yeah</name>
...
All I did to clean it up was run it through a re-formatter like xmlstarlet as I mentioned in my comment. Note: you don't have to reformat it for java to read it if it's well formed. Human readable is all a re-format does for you.
The first xpath query gets the track name using a path lfm/tracks/track/name. You can use something like this xpath tester to try out your xpath queries (you can paste your xml in and it will reformat it too). If you don't understand xpath, there are many sources on the net.
The second xpath works relative to the current track name node, and looks for a following-sibling node of type artist with a name sub-node, and then displays the text of the node.
Here's the code
package net.fish;
import java.net.URL;
import java.net.URLConnection;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class ParseXML {
private static final DocumentBuilderFactory DOCUMENT_BUILDER_FACTORY = DocumentBuilderFactory.newInstance();
private static final XPathFactory XPATH_FACTORY = XPathFactory.newInstance();
public static void main(String[] args) throws Exception {
new ParseXML().parseXml("http://ws.audioscrobbler.com/2.0/?method=chart.gethypedtracks&api_key=1732077d6772048ccc671c754061cb18&limit=10");
}
private void parseXml(String urlPath) throws Exception {
URL url = new URL(urlPath);
URLConnection connection = url.openConnection();
DocumentBuilder db = DOCUMENT_BUILDER_FACTORY.newDocumentBuilder();
final Document document = db.parse(connection.getInputStream());
XPath xPathEvaluator = XPATH_FACTORY.newXPath();
XPathExpression nameExpr = xPathEvaluator.compile("lfm/tracks/track/name");
NodeList trackNameNodes = (NodeList) nameExpr.evaluate(document, XPathConstants.NODESET);
for (int i = 0; i < trackNameNodes.getLength(); i++) {
Node trackNameNode = trackNameNodes.item(i);
System.out.println(String.format("Track Name: %s" , trackNameNode.getTextContent()));
XPathExpression artistNameExpr = xPathEvaluator.compile("following-sibling::artist/name");
NodeList artistNameNodes = (NodeList) artistNameExpr.evaluate(trackNameNode, XPathConstants.NODESET);
for (int j=0; j < artistNameNodes.getLength(); j++) {
System.out.println(String.format(" - Artist Name: %s", artistNameNodes.item(j).getTextContent()));
}
}
}
}
Related
I want to manipulate xml doc having default namespace but no prefix. Is there a way to use xpath without namespace uri just as if there is no namespace?
I believe it should be possible if we set namespaceAware property of documentBuilderFactory to false. But in my case it is not working.
Is my understanding is incorrect or I am doing some mistake in code?
Here is my code:
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(false);
try {
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document dDoc = builder.parse("E:/test.xml");
XPath xPath = XPathFactory.newInstance().newXPath();
NodeList nl = (NodeList) xPath.evaluate("//author", dDoc, XPathConstants.NODESET);
System.out.println(nl.getLength());
} catch (Exception e) {
e.printStackTrace();
}
Here is my xml:
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns="http://www.mydomain.com/schema">
<author>
<book title="t1"/>
<book title="t2"/>
</author>
</root>
The XPath processing for a document that uses the default namespace (no prefix) is the same as the XPath processing for a document that uses prefixes:
For namespace qualified documents you can use a NamespaceContext when you execute the XPath. You will need to prefix the fragments in the XPath to match the NamespaceContext. The prefixes you use do not need to match the prefixes used in the document.
http://download.oracle.com/javase/6/docs/api/javax/xml/namespace/NamespaceContext.html
Here is how it looks with your code:
import java.util.Iterator;
import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
public class Demo {
public static void main(String[] args) {
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
try {
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document dDoc = builder.parse("E:/test.xml");
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext(new MyNamespaceContext());
NodeList nl = (NodeList) xPath.evaluate("/ns:root/ns:author", dDoc, XPathConstants.NODESET);
System.out.println(nl.getLength());
} catch (Exception e) {
e.printStackTrace();
}
}
private static class MyNamespaceContext implements NamespaceContext {
public String getNamespaceURI(String prefix) {
if("ns".equals(prefix)) {
return "http://www.mydomain.com/schema";
}
return null;
}
public String getPrefix(String namespaceURI) {
return null;
}
public Iterator getPrefixes(String namespaceURI) {
return null;
}
}
}
Note:
I also used the corrected XPath suggested by Dennis.
The following also appears to work, and is closer to your original question:
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
public class Demo {
public static void main(String[] args) {
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document dDoc = builder.parse("E:/test.xml");
XPath xPath = XPathFactory.newInstance().newXPath();
NodeList nl = (NodeList) xPath.evaluate("/root/author", dDoc, XPathConstants.NODESET);
System.out.println(nl.getLength());
} catch (Exception e) {
e.printStackTrace();
}
}
}
Blaise Doughan is right, attached code is correct.
Problem was somewhere elese. I was running all my tests through Application launcher in Eclipse IDE and nothing was working. Then I discovered Eclipse project was cause of all grief. I ran my class from command prompt, it worked. Created a new eclipse project and pasted same code there, it worked there too.
Thank you all guys for your time and efforts.
I've written a simple NamespaceContext implementation (here), that might be of help. It takes a Map<String, String> as input, where the key is a prefix, and the value is a namespace.
It follows the NamespaceContext spesification, and you can see how it works in the unit tests.
Map<String, String> mappings = new HashMap<>();
mappings.put("foo", "http://foo");
mappings.put("foo2", "http://foo");
mappings.put("bar", "http://bar");
context = new SimpleNamespaceContext(mappings);
context.getNamespaceURI("foo"); // "http://foo"
context.getPrefix("http://foo"); // "foo" or "foo2"
context.getPrefixes("http://foo"); // ["foo", "foo2"]
Note that it has a dependency on Google Guava
I want to convert a dom nodelist to a json array and send the result to a rest client:
Each node of the xml represents the following:
<A NAME="x" COUNT="y">
<B KEY="z1" VALUE="z2"/>
<B KEY="z3" VALUE="z4"/>
</A>
I want that i i will have for the output an array of objects where each object looks like the following:
{"NAME":"x",
"COUNT":"y",
"B": [ {"KEY": "z1, VALUE:"z2"},
{"KEY":"z3", VALUE:"z4"} ]
}
I tried to use the GSON library:
package com.a;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class Test {
private static final String XPATH = "/A/B";
public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException, XPathExpressionException {
File f = new File("C:/Users/abc/Desktop/a.xml");
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = null;
builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(f);
XPath xPath = XPathFactory.newInstance().newXPath();
NodeList nodeList = (NodeList) xPath.compile(XPATH).evaluate(xmlDocument, XPathConstants.NODESET);
Gson gson = new GsonBuilder().setPrettyPrinting().create();
String jsonOutput = gson.toJson(nodeList);
System.out.println(jsonOutput);
}
}
but i am getting an error
Exception in thread "main" java.lang.StackOverflowError at
java.lang.StringBuffer.append(StringBuffer.java:224) at
java.io.StringWriter.write(StringWriter.java:84) at
com.google.gson.stream.JsonWriter.newline(JsonWriter.java:569) at
com.google.gson.stream.JsonWriter.beforeName(JsonWriter.java:586)
How can i fix this code?
As it is possible to convert a whole xml to json (Quickest way to convert XML to JSON in Java)
I assume that it is possible to convert dom nodes to json. What is wrong here?
What's wrong ? you simply don't use the lib described on your link (Quickest way to convert XML to JSON in Java)
Gson will use java reflection to generate a json string from any object. From a DOM Document (or node), even when it doesn't end up with a StackOverflowError, it will not produce what you expect. here is the result for your XML:
{"fNamespacesEnabled":false,"mutationEvents":false,"actualEncoding":"UTF-8","standalone":false,"fDocumentURI":"...a.xml","changes":0,"allowGrammarAccess":false,"errorChecking":true,"ancestorChecking":true,"xmlVersionChanged":false,"documentNumber":0,"nodeCounter":0,"xml11Version":false,"flags":6}
Actually it seems that if any method has been invoked on a DOM Document (ex: getDocumentElement), the gson.toJson end up with a StackOverflowError.
As you can see in the link, a jar that will do the job can be found here: http://mvnrepository.com/artifact/org.json/json
It implies that you re-convert the nodes extracted with your XPath to string.
You can do it with that:
private static String toString(Node n) throws TransformerFactoryConfigurationError, TransformerException {
Transformer transformer = TransformerFactory.newInstance().newTransformer();
StreamResult result = new StreamResult(new StringWriter());
DOMSource source = new DOMSource(n);
transformer.transform(source, result);
return result.getWriter().toString();
}
With all that, all you have to do is to loop through your nodeList, convert it to string, and then convert it to json
for (int i = 0; i < nodeList.getLength(); i++) {
Node n = nodeList.item(i);
JSONObject xmlJSONObj = XML.toJSONObject(toString(n));
String jsonPrettyPrintString = xmlJSONObj.toString(1);
System.out.println(jsonPrettyPrintString);
}
I am following some tutorials to make a XML Parser..
I can't get futher because it says the method getElementsByTagName() is undefined for the type Document.
what did i do wrong?
import org.jdom2.Document;
import org.jdom2.input.SAXBuilder;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;
public class Parser {
public static void main(String[] args) {
try {
SAXBuilder parser = new SAXBuilder();
Document doc =
parser.build("http://developerlife.com/xmljavatutorial1/AddressBook.xml");
NodeList listOfPersons = doc.getElementsByTagName("PERSON");
int numberOfPersons = listOfPersons.getLength();
} catch (Exception e){}
}
}
You first need to take a reference to the root element of your document. Try this:
Element root = doc.getDocumentElement();
NodeList listOfPersons = root.getElementsByTagName("PERSON");
Your Element class is using the DOM, while your Document class is using JDOM2. It's not clear whether your intent is to use DOM or JDOM2, but I doubt that you intended to mix them. Check your import statements.
(If you haven't decided yet, JDOM2 is much preferable.)
I am trying to use the namespace-uri() function in XPath to retrieve nodes based on their fully qualified name. The query //*[local-name() = 'customerName' and namespace-uri() = 'http://example.com/officeN'] in this online XPath tester, among others, correctly returns the relevant nodes. Yet the following self-contained Java class does not retrieve anything. What am I doing wrong with namespace-uri()?
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
public class Test{
public static void main(String[] args)throws Exception {
XPathExpression expr = XPathFactory.newInstance().newXPath().compile(
"//*[local-name() = 'customerName' and namespace-uri() = 'http://example.com/officeN']");
String xml=
"<Agents xmlns:n=\"http://example.com/officeN\">\n"+
"\t<n:Agent>\n\t\t<n:customerName>Joe Shmo</n:customerName>\n\t</n:Agent>\n"+
"\t<n:Agent>\n\t\t<n:customerName>Mary Brown</n:customerName>\n\t</n:Agent>\n</Agents>";
System.out.println(xml);
Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
System.err.println("\n\nNodes:");
for (int i = 0; i < nodes.getLength(); i++) {
System.err.println(nodes.item(i));
}
}
}
The query looks fine. You also need to declare your DocumentBuilderFactory to be "namespace-aware".
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
dbf.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
My goal is executing an XQuery using XPath.
My XML file is:
<?xml version="1.0" encoding="UTF-8"?>
<postes>
<poste>
<gouvernourat>Kairouan</gouvernourat>
<ville>Kairouan sud</ville>
<cp>3100</cp>
</poste>
<poste>
<gouvernourat>Tunis</gouvernourat>
<ville>Ghazela</ville>
<cp>1002</cp>
</poste>
</postes>
My Java code is:
package xmlparse;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class QueryXML {
public void query() throws ParserConfigurationException, SAXException,
IOException, XPathExpressionException {
// Standard of reading a XML file
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder;
Document doc = null;
XPathExpression expr = null;
builder = factory.newDocumentBuilder();
doc = builder.parse("a.xml"); //C:\\Users\\aymen\\Desktop\\
// Create a XPathFactory
XPathFactory xFactory = XPathFactory.newInstance();
// Create a XPath object
XPath xpath = xFactory.newXPath();
// Compile the XPath expression
expr = xpath.compile("/postes/poste[gouvernourat='Tunis']/ville/text()");
// Run the query and get a nodeset
Object result = expr.evaluate(doc, XPathConstants.NODESET);
// Cast the result to a DOM NodeList
NodeList nodes = (NodeList) result;
for (int i=0; i<nodes.getLength();i++){
System.out.println(nodes.item(i).getNodeValue());
}
}
public static void main(String[] args) throws XPathExpressionException, ParserConfigurationException, SAXException, IOException {
QueryXML process = new QueryXML();
process.query();
}
}
When I launch this Java code the result is displayed on the console correctly (System.out.println).
But if I copy this code to my Android application and change System.out.println(nodes.item(i).getNodeValue()); to Text2.setText(nodes.item(i).getNodeValue()); (I have a TextView named Text2)
When I execute the code and I click the button the TextView stays empty (No error for Force Close)
Thank you in advance
Attribute names needs to start with '#' while using XPath in Android.
So change
[gouvernourat='Tunis']
To
[#gouvernourat='Tunis']
Refer http://developer.android.com/reference/javax/xml/xpath/package-summary.html for details.