Generating a Response

Besides the request object, the container passes an object that implements the HttpServletResponse interface as an argument to the doGet( ) and doPost( ) methods. This interface defines methods for getting a writer or stream for the response body. It also defines methods for setting the response status code and headers. Example 19-3 contains the code for a servlet that uses some of the methods.

Example 19-3. Using HttpServletResponse methods
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
  
public class HelloMIME extends HttpServlet {
    private static final int TEXT_TYPE = 0;
    private static final int IMAGE_TYPE = 1;
  
    public void doGet(HttpServletRequest request, 
        HttpServletResponse response) 
        throws ServletException, IOException {
  
        String greeting = "Hello World!";
        int majorType = TEXT_TYPE;
        String type = request.getParameter("type");
        if ("plain".equals(type)) {
            response.setContentType("text/plain");
        }
        else if ("html".equals(type)) {
            response.setContentType("text/html");
            greeting = "<html><body><h1>" + greeting +
                "</h1></body></html>";
        }
        else if ("image".equals(type)) {
            response.setContentType("image/gif");
            majorType = IMAGE_TYPE;
        }
        else {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, 
                "Please specify a valid response type");
            return;
        }
  
        if (majorType == TEXT_TYPE) {
            PrintWriter out = response.getWriter(  );
            out.println(greeting);
        }
        else {
            OutputStream os = response.getOutputStream(  ); ServletContext application = getServletContext( ); InputStream ...

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