parsing XML from URL in java

Question

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)

Guenther · Accepted Answer · 2016-08-11 19:46:22Z

2

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

answered Aug 11, 2016 at 19:46

Guenther

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1 Comment

JBoy Over a year ago

f.setNamespaceAware(false); and f.setValidating(false); can be omitted as their default values is false

vempo · Accepted Answer · 2016-08-11 19:30:49Z

1

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.

answered Aug 11, 2016 at 19:30

vempo

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1 Comment

waszgie Over a year ago

thank you very much you save my life !! you are great !!

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