CODEWITHSUNDEEP
javaxml
gadzik
gadzik

Reputation: 47

parsing XML from URL in java

Hello i have a big problem . i have to parse XML file from URL/HTTP and work on it in java , but i get exception always when i do it . address is ok because it is www of a bank . please help me 

import java.net.URL;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;

public class MainClass {
public static void main(String [] args){
    String url = "http://api.nbp.pl/api/exchangerates/rates/c/gbp/2015-01-01/2015-01-31";   
    try
    {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(new URL(url).openStream());

        doc.getDocumentElement().normalize();
        System.out.println ("Root element: " + 
                    doc.getDocumentElement().getNodeName());

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
}
}

error :

[Fatal Error] :1:1: Content is not allowed in prolog. org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) at javax.xml.parsers.DocumentBuilder.parse(Unknown Source) at pl.parser.nbp.MainClass.main(MainClass.java:17)

and second case :

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class MainClass {
public static void main(String [] args){
    String url = "http://api.nbp.pl/api/exchangerates/rates/a/gbp/2012-01-01/2012-01-31/";   
    try
    {
        DocumentBuilderFactory f = 
                DocumentBuilderFactory.newInstance();
        DocumentBuilder b = f.newDocumentBuilder();
        Document doc = b.parse(url);

        doc.getDocumentElement().normalize();
        System.out.println ("Root element: " + 
                    doc.getDocumentElement().getNodeName());

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
}
}

error :

[Fatal Error] :1:1: Content is not allowed in prolog. org.xml.sax.SAXParseException; systemId: http://api.nbp.pl/api/exchangerates/rates/a/gbp/2012-01-01/2012-01-31/; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) at javax.xml.parsers.DocumentBuilder.parse(Unknown Source) at pl.parser.nbp.MainClass.main(MainClass.java:19)

Upvotes: 2

Views: 10966

Answers (2)

Guenther
Guenther

Reputation: 2045

The problem is that readind directly from the URL, the site will return the data in json format. You need to open the URL, requesting xml

public static void main(String [] args){
    String url = "http://api.nbp.pl/api/exchangerates/rates/a/gbp/2012-01-01/2012-01-31/";
    DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
    f.setNamespaceAware(false);
    f.setValidating(false);
    DocumentBuilder b = f.newDocumentBuilder();
    URLConnection urlConnection = new URL(url).openConnection();
    urlConnection.addRequestProperty("Accept", "application/xml");
    Document doc = b.parse(urlConnection.getInputStream());
    doc.getDocumentElement().normalize();
    System.out.println ("Root element: " +  doc.getDocumentElement().getNodeName());
}

This will print 

Root element: ExchangeRatesSeries

Upvotes: 2

vempo
vempo

Reputation: 3153

By default, the URL returns data in JSON format. You see an XML in the browser because the way the browser negotiates a return type (via Accept header).

You can either parse the data as JSON, or change the URL to http://api.nbp.pl/api/exchangerates/rates/c/gbp/2015-01-01/2015-01-31?format=xml.

Notice ?format=xml at the end.

See the User manual.

Upvotes: 1

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