java - Why am I getting this error Premature end of file?

Question

I am trying to parse an XML response, but I am failing miserably. I thought initially that the xml was just not being returned in the response, so I crafted up the code below with a direct link to my xml file online. I am able to print the XML to screen with no problems. However when I call my parse method I get Premature end of file.

It works if I pass the URL directly:

• builder.parse("");

but fails when I passed an InputStream:

• builder.parse(connection.getInputStream());

    try {
      URL url = new URL(xml);
      URLConnection uc =  url.openConnection();
      HttpURLConnection  connection = (HttpURLConnection )uc;
  
      connection.setDoInput(true);
      connection.setDoOutput(true);
  
      InputStream instream;
      InputSource source;
      //get XML from InputStream
      if(connection.getResponseCode()>= 200){
          connection.connect();       
          instream = connection.getInputStream();         
          parseDoc(instream);     
      }
      else{
          instream = connection.getErrorStream();
      }
  
  
  } catch (MalformedURLException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (ParserConfigurationException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (SAXException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  }
  
  
  
   static void parseDoc(InputStream instream) throws ParserConfigurationException,
   SAXException, IOException{
  
  
    BufferedReader buff_read = new BufferedReader(new InputStreamReader(instream,"UTF-8"));
      String  inputLine = null;
  
      while((inputLine = buff_read.readLine())!= null){
          System.out.println(inputLine);
      }
  
    DocumentBuilderFactory factory =DocumentBuilderFactory.newInstance();
    factory.isIgnoringElementContentWhitespace();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(instream);
  }
  

The errors I am getting:

    [Fatal Error] :1:1: Premature end of file.
org.xml.sax.SAXParseException: Premature end of file.
    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 com.ameba.api.network.MainApp.parseDoc(MainApp.java:78)
    at com.ameba.api.network.MainApp.main(MainApp.java:41)

Answer 1

When you do this,

while((inputLine = buff_read.readLine())!= null){
        System.out.println(inputLine);
    }

You consume everything in instream, so instream is empty. Now when try to do this,

Document doc = builder.parse(instream);

The parsing will fail, because you have passed it an empty stream.