Parsing a XML HttpResponse

Question

I'm trying to parse the XML HttpResponse i get from a HttpPost to a server (last.fm), for a last.fm android app. If i simply parse it to string i can see it being a normal xml string, with all the desired information. But i just cant parse the single NameValuePairs. This is my HttpResponse object:

HttpResponse response = client.execute(post);
HttpEntity r_entity = response.getEntity();

I tried two different things and non of them worked. First i tried to retrieve the NameValuePairs:

List<NameValuePair> answer = URLEncodedUtils.parse(r_entity);
String name = "empty";
String playcount = "empty";
for (int i = 0; i < answer.size(); i++){
   if (answer.get(i).getName().equals("name")){
      name = answer.get(i).getValue();
   } else if (answer.get(i).getName().equals("playcount")){
      playcount = answer.get(i).getValue();
   }
}

After this code, name and playcount remain "empty". So i tried to use a XML Parser:

DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document answer = db.parse(new DataInputStream(r_entity.getContent()));
NodeList nl = answer.getElementsByTagName("playcount");
String playcount = "empty";
for (int i = 0; i < nl.getLength(); i++) {
   Node n = nl.item(i);
   Node fc = n.getFirstChild();
   playcount Url = fc.getNodeValue();
}

This seems to fail much earlier since it doesn't even get to setting the playcount variable. But like i said if i perform this:

EntityUtils.toString(r_entity);

I will get a perfect xml string. So it should no problem to pars it since the HttpResponse contains the correct information. What am i doing wrong?

Answer 1

if (answer.get(i).getName() == "name"){

You can't use == to compare a String

When we use the == operator, we are actually comparing two object references, to see if they point to the same object. We cannot compare, for example, two strings for equality, using the == operator. We must instead use the .equals method, which is a method inherited by all classes from java.lang.Object.

Here's the correct way to compare two strings.

 String abc = "abc"; String def = "def";

// Bad way
if ( (abc + def) == "abcdef" )
 {
   ......
 }
 // Good way
 if ( (abc + def).equals("abcdef") )
 {
  .....
 }

Taken from Top Ten Errors Java Programmers Make

Answer 2

I solved it. The DOM XML parser needed a little more adjustment:

        HttpResponse response = client.execute(post);
        HttpEntity r_entity = response.getEntity();
        String xmlString = EntityUtils.toString(r_entity);
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = factory.newDocumentBuilder();
        InputSource inStream = new InputSource();
        inStream.setCharacterStream(new StringReader(xmlString));
        Document doc = db.parse(inStream);  

        String playcount = "empty";
        NodeList nl = doc.getElementsByTagName("playcount");
        for(int i = 0; i < nl.getLength(); i++) {
            if (nl.item(i).getNodeType() == org.w3c.dom.Node.ELEMENT_NODE) {
                 org.w3c.dom.Element nameElement = (org.w3c.dom.Element) nl.item(i);
                 playcount = nameElement.getFirstChild().getNodeValue().trim();
             }
        }

Answer 3

This is a very good tutorial on parsing XML from a feed. You can use it to build more robust apps that need to parse XML feeds I hope it helps