Protocol error trying to parse XML response in Java

I am successfully making an API call that is a SOAP request with an account number in the body. I connected using Httpurlconnection and I am reading those results using BufferedReader:

if (responseCode == HttpURLConnection.HTTP_OK) {​​​​​ // success
    BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
    String inputLine;
    StringBuffer response = new StringBuffer();
    while ((inputLine = in.readLine()) != null) {​​​​​
    {​​​​​
        sb.append(inputLine).append("n");
        String xml2String = sb.toString();

Then using documentbuilderfactory to build the doc to read into the parser:

DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = dbFactory.newDocumentBuilder();
Document xmlDom = docBuilder.parse(new InputSource(inputLine));

And then try to parse:

DOMParser parser = new DOMParser();
parser.parse(new InputSource(new StringReader(returnList.item(0).getTextContent())));
Document doc = parser.getDocument();
NodeList responsedata = doc.getDocumentElement().getChildNodes();

NodeList returnList = xmlDom.getElementsByTagName(“DATA”);

// Get the DATA
DOMParser parser = new DOMParser();
parser.parse(new InputSource(new StringReader(returnList.item(0).getTextContent())));
Document doc = parser.getDocument();
NodeList responsedata = doc.getDocumentElement().getChildNodes();

This is the error I get (which includes the output from the API request):

Exception,no protocol:
{​​​​​"d":"<DATA><BussFlds><FieldName>FirstName</FieldName><Value><![CDATA[TESTY]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>LastName</FieldName><Value><![CDATA[TESTER]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>TYPE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>DATE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>CUSTCODE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>PREMCODE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>ADDRESS</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>CITY</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>STATE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>ZIP</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>ZIP4</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>ACCTBALANCE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>PASTDUE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds><BussFlds><FieldName>PHONE</FieldName><Value><![CDATA[]]></Value><DataType>String</DataType><Format></Format><Editable>True</Editable></BussFlds></DATA>"}​​​​​

I suspect that it is that curly bracket data on the first row or missing header information but I am not sure if that is the issue or how to fix it. Thanks!

Answer

This response:

{"d":"<DATA><BussFlds>…

is not XML. You cannot read it with a DocumentBuilder.

That response is in a format known as JSON. You cannot use an XML parser to read it.

So, you will want to pass the response to a JSON parser, not an XML parser.

A JSON “object” is basically a dictionary (that is, a lookup table) with string keys. Your response has exactly one entry, whose key is "d". So you first need to parse the response as JSON:

String xml;
try (JsonParser jsonParser = Json.createParser(con.getInputStream())) {
    xml = jsonParser.getObject().getString("d");
}

(There are other JSON parsing libraries available. I chose the one that is part of Java EE for the above example.)

Notice that the code does not attempt to read con.getInputStream() as a string first. There is no benefit to doing that. The parser accepts an InputStream directly. Which means there is no need to use InputStreamReader, or BufferedReader, or StringBuffer.

Now that you have XML content in the xml variable, you can parse it with DocumentBuilder:

DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = dbFactory.newDocumentBuilder();
Document xmlDom = docBuilder.parse(new InputSource(new StringReader(xml)));

Side note: You should never use StringBuffer. Use StringBuilder instead. StringBuffer is a 26-year-old class that was part of Java 1.0, and it is designed for multithreaded use, which is almost never needed, and which adds a lot of overhead.