❌ No, you cannot use both PrintWriter and ServletOutputStream simultaneously in a servlet for the same response.

It is forbidden by the Servlet specification.
Mixing them causes IllegalStateException.

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🧠 Why?

• The response can either be character-based (PrintWriter) or byte-based (ServletOutputStream).
• Not both.
• Once you get one, the underlying response output handling is set (to either character encoding mode or binary mode).
• Mixing would break the HTTP response stream.

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⚡ Example of what NOT to do:

protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    
    PrintWriter writer = response.getWriter();
    ServletOutputStream outputStream = response.getOutputStream(); // ❌ WRONG!
}

✅ As soon as you call response.getWriter(), trying to call response.getOutputStream() will throw an exception at runtime.

Or vice versa.

🎯 Servlet Specification (Official) says:

If getWriter() has been called, then calling getOutputStream() must throw an IllegalStateException, and vice versa.

🚀 How to decide which one to use?

Situation	Use
You send text (HTML, JSON, plain text)	PrintWriter
You send binary data (images, PDFs, zip files)	ServletOutputStream

✅ Always pick one early when building the response, depending on what you’re sending.

🛠️ Correct usage examples

✅ Use only PrintWriter:

protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html; charset=UTF-8");
    PrintWriter out = response.getWriter();
    out.println("<h1>Hello World!</h1>");
}

✅ Use only ServletOutputStream:

protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("application/octet-stream");
    ServletOutputStream out = response.getOutputStream();
    out.write(new byte[]{1, 2, 3, 4});
}

🔥 Super Quick Summary:

	PrintWriter	ServletOutputStream
Type	Character stream	Byte stream
getWriter() locks response into	Character mode
getOutputStream() locks response into	Binary mode
Use both together?	❌ NO, IllegalStateException