AsyncReadServlet.java

package me.chanjar.learning;

import org.apache.commons.lang3.exception.ExceptionUtils;

import javax.servlet.AsyncContext;
import javax.servlet.ReadListener;
import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(value = "/async-read", asyncSupported = true)
public class AsyncReadServlet extends HttpServlet {

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    System.out.println("Servlet thread: " + Thread.currentThread().getName());
    AsyncContext asyncCtx = req.startAsync();
    ServletInputStream is = req.getInputStream();
    is.setReadListener(new ReadListener() {
      private int totalReadBytes = 0;

      @Override
      public void onDataAvailable() {
        System.out.println("ReadListener thread: " + Thread.currentThread().getName());

        try {
          byte buffer[] = new byte[1 * 1024];
          int readBytes = 0;
          while (is.isReady() && !is.isFinished()) {
            int length = is.read(buffer);
            if (length == -1 && is.isFinished()) {
              asyncCtx.complete();
              System.out.println("Read: " + readBytes + " bytes");
              System.out.println("Total Read: " + totalReadBytes + " bytes");
              return;
            }
            readBytes += length;
            totalReadBytes += length;

          }
          System.out.println("Read: " + readBytes + " bytes");

        } catch (IOException ex) {
          ex.printStackTrace();
          asyncCtx.complete();
        }
      }

      @Override
      public void onAllDataRead() {
        try {
          System.out.println("Total Read: " + totalReadBytes + " bytes");
          asyncCtx.getResponse().getWriter().println("Finished");
        } catch (IOException ex) {
          ex.printStackTrace();
        }
        asyncCtx.complete();
      }

      @Override
      public void onError(Throwable t) {
        System.out.println(ExceptionUtils.getStackTrace(t));
        asyncCtx.complete();
      }
    });

  }

}