Threads not waiting for I/O operations to finish

• Introduced in 1.4
• Enhanced in java 1.7
• Netty - a non-blocking I/O client-server framework

With traditional IO if streamed data is slower than the server can read then the server thread is waiting for that data

                public class BlockingIoServlet extends HttpServlet {
                    protected void doGet(HttpServletRequest request, HttpServletResponse response)
                         throws IOException, ServletException {     
                 ServletInputStream input = request.getInputStream();
                       byte[] b = new byte[1024];
                       int len = -1;
                       while ((len = input.read(b)) != -1) {
                          . . . 
                       }
                   }
                }
                

Servlet 3.1 enhancements

• Ability to register EventListeners
• Ability to check Input/Output Stream readiness
• Ability to check Input/Output Stream compleetnes

ServletInputStream has the ability to regiser a ReadListener

                AsyncContext context = request.startAsync();
                ServletInputStream input = request.getInputStream();
                input.setReadListener(new MyReadListener(input, context));
              

ServletOutputStream has the ability to regiser a WriteListener

                AsyncContext context = request.startAsync();
                ServletOutputStream responeOutput = response.getOutputStream();

                responeOutput.setWriteListener(new WriteListener() { 
                    @Override
                    public void onWritePossible() throws IOException {
                      while (responeOutput.isReady()) { 
                        // write
                      }
                    }
                    @Override
                    public void onError(Throwable t) { 
                      // Error handling
                      context.complete();
                    }
                  });
              
              

• Instructions Starter with blocking I/O
• Step1 Starter with blocking I/O
• Step2 Non-Blocking Upload
• Step3 Non-Blocking Download