ignoring DOCTYPE from xml String

I am trying to ignore the DOCTYPE declaration in the input xmlstring and parse it using a DTD from fixed location .
For ex: Instead of using <xml version='1.0'><DOCTYPE INPUT SYSTEM "file//localhost/../../../ex.dtd">
I want to use <xml version='1.0'><DOCTYPE INPUT SYSTEM "ex.dtd"> and make the parser get the dtd from a fixed location.
How can i do it..?I know theres a work around for this by playing with Strings .I want to know if theres a any way we can configure this in the parser itself . Portion of the code is as below ..

java.io.InputStream input=null;
input=new java.io.ByteArrayInputStream(xmlString.getBytes());
out = new OutputStreamWriter (System.out, "UTF8");
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true);
factory.newSAXParser().parse( input, new xmlHandler());

Thx in advance ...
prabhu