StreamSource and StreamResult

The StreamSource and StreamResult classes are used as sources and targets for transforms from sequences of bytes and characters. This includes streams, readers, writers, strings, and files. What unifies these is that none of them know they contain an XML document. Indeed, on input they may not always contain an XML document. If so, an exception will be thrown as soon as you attempt to build a Transformer or a Templates object from the StreamSource.

package javax.xml.transform.stream;

public class StreamSource implements Source {

  public static final String FEATURE =
   "http://javax.xml.transform.stream.StreamSource/feature";

  public StreamSource();
  public StreamSource(InputStream inputStream);
  public StreamSource(InputStream inputStream, String systemID);
  public StreamSource(Reader reader);
  public StreamSource(Reader reader, String systemID);
  public StreamSource(String systemID);
  public StreamSource(File f);
  
  public void        setInputStream(InputStream inputStream);
  public InputStream getInputStream();
  public void        setReader(Reader reader);
  public Reader      getReader();
  public void        setPublicId(String publicID);
  public String      getPublicId();
  public void        setSystemId(String systemID);
  public String      getSystemId();
  public void        setSystemId(File f);
  
}

You should not specify both an InputStream and a Reader. If you do, which one the processor reads from is implementation dependent. If neither an InputStream nor a Reader is available, then the processor will attempt to open a connection to the URI specified by the system ID. You should set the system ID even if you do specify an InputStream or a Reader because this will be needed to resolve relative URLs that appear inside the stylesheet and input document.

package javax.xml.transform.stream;

public class StreamResult implements Result

  public static final String FEATURE =
   "http://javax.xml.transform.stream.StreamResult/feature";

  public StreamResult() {}
  public StreamResult(OutputStream outputStream);
  public StreamResult(Writer writer);
  public StreamResult(String systemID);
  public StreamResult(File f);
  
  public void         setOutputStream(OutputStream outputStream);
  public OutputStream getOutputStream();
  public void         setWriter(Writer writer);
  public Writer       getWriter();
  public void         setSystemId(String systemID);
  public void         setSystemId(File f);
  public String       getSystemId();
  
}

You should specify the system ID URL and one of the other identifiers (File, OutputStream, Writer, or String.) If you specify more than one possible target, which one the processor chooses is implementation dependent.