Buffering

• Guessing the right length is hard. Instead, write to a buffer. Server sets the Content-Length automatically. Set by:

  public void ServletResponse.setBufferSize(int size);

• You can get the current buffer size with

  public int ServletResponse.getBufferSize();

• You can find out it has already been committed with

  public boolean ServletResponse.isCommitted();

• And call reset() to clear it. Here is an example:

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class Buffering extends HttpServlet {

  public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    res.setBufferSize(8 * 1024); // 8K buffer
    res.setContentType("text/html");
    PrintWriter out = res.getWriter();

    int size = res.getBufferSize(); // returns 8096 or greater

    out.println("The client won't see this");
    res.reset();
    out.println("Nor will the client see this!");
    res.reset();
    out.println("And this won't be seen if sendError() is called");
    if (req.getParameter("important_parameter") == null) {
      res.sendError(res.SC_BAD_REQUEST, "important_parameter needed");
    }
  }
}