Recuperar XML de URL

Tengo algunos problemas para recuperar un xml de la URL con el siguiente código:

    private static String getAlbumArt(String artistName, String albumName){
        try{
        XMLParser xml_parser = new XMLParser();
        String xml = xml_parser.getXmlFromUrl(getAlbumURL(artistName, albumName));
        Document doc = xml_parser.getDomElement(xml);
        NodeList N = doc.getElementsByTagName("album");
        Node node = N.item(0);
        NodeList N2 = node.getChildNodes();
        System.out.println("1------");
            for (int i = 0; i < N2.getLength(); i++) {
                Node detailNode = N2.item(i);
                if (detailNode.getNodeType() == Node.ELEMENT_NODE)
                    {
                    System.out.println("2------");
                    if (detailNode.getNodeName().equalsIgnoreCase("image")) 
                    {
                        String sizeVal = ((Element) detailNode).getAttribute("size");
                        String url = detailNode.getTextContent();
                        if (sizeVal.equalsIgnoreCase("large")) {
                            return url;
                        }
                    }
                    }
        }
        }
        catch (Exception e){
        }
        return null;
    }

La función xml a la que llamo en el código anterior:

public String getXmlFromUrl(String url) {
    String xml = null;
    try {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        xml = EntityUtils.toString(httpEntity);
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return xml;
}

getAlbumURL:

    public static String getAlbumURL(String artist, String album){
        return URL_METHOD + METHOD_GETALBUM + AMPERSAND
                + API_KEY + AMPERSAND
                + PARAM_ARTIST + artist + AMPERSAND
                + PARAM_ALBUM + album;
    }

Analizador XML:

XMLParser de clase pública {

// constructor
public XMLParser() {
}

//Get XML from URL
public String getXmlFromUrl(String url) {
    String xml = null;
    try {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        xml = EntityUtils.toString(httpEntity);
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return xml;
}

//Get dom element
public Document getDomElement(String xml){
    Document doc = null;
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    try {

        DocumentBuilder db = dbf.newDocumentBuilder();
        InputSource is = new InputSource();
            is.setCharacterStream(new StringReader(xml));
            doc = db.parse(is); 

        } 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 doc;
}

//Get nod element
 public final String getElementValue(Node elem ) {
     Node child;
     if( elem != null){
         if (elem.hasChildNodes()){
             for( child = elem.getFirstChild(); child != null; child = child.getNextSibling() ){
                 if( child.getNodeType() == Node.TEXT_NODE  ){
                     return child.getNodeValue();
                 }
             }
         }
     }
     return "";
 }

//Get element value
 public String getValue(Element item, String str) {     
     NodeList nlList = item.getElementsByTagName(str).item(0).getChildNodes();
     Node nValue = (Node) nlList.item(0);
     return nValue.getNodeValue();
    }

}

Algunas ideas ? En serio, no sé qué está mal. Utilicé esto antes y funcionó.