/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package nonblocking;
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import java.io.IOException;
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import java.nio.charset.StandardCharsets;
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import javax.servlet.AsyncContext;
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import javax.servlet.ReadListener;
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import javax.servlet.ServletException;
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import javax.servlet.ServletInputStream;
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import javax.servlet.ServletOutputStream;
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import javax.servlet.WriteListener;
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import javax.servlet.http.HttpServlet;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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/**
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* This doesn't do anything particularly useful - it just counts the total
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* number of bytes in a request body while demonstrating how to perform
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* non-blocking reads.
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*/
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public class ByteCounter extends HttpServlet {
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private static final long serialVersionUID = 1L;
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@Override
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protected void doGet(HttpServletRequest req, HttpServletResponse resp)
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throws ServletException, IOException {
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resp.setContentType("text/plain");
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resp.setCharacterEncoding("UTF-8");
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resp.getWriter().println("Try again using a POST request.");
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}
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@Override
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protected void doPost(HttpServletRequest req, HttpServletResponse resp)
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throws ServletException, IOException {
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resp.setContentType("text/plain");
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resp.setCharacterEncoding("UTF-8");
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// Non-blocking IO requires async
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AsyncContext ac = req.startAsync();
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// Use a single listener for read and write. Listeners often need to
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// share state to coordinate reads and writes and this is much easier as
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// a single object.
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@SuppressWarnings("unused")
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CounterListener listener = new CounterListener(
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ac, req.getInputStream(), resp.getOutputStream());
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}
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/**
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* Keep in mind that each call may well be on a different thread to the
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* previous call. Ensure that changes in values will be visible across
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* threads. There should only ever be one container thread at a time calling
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* the listener.
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*/
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private static class CounterListener implements ReadListener, WriteListener {
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private final AsyncContext ac;
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private final ServletInputStream sis;
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private final ServletOutputStream sos;
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private volatile boolean readFinished = false;
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private volatile long totalBytesRead = 0;
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private byte[] buffer = new byte[8192];
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private CounterListener(AsyncContext ac, ServletInputStream sis,
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ServletOutputStream sos) {
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this.ac = ac;
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this.sis = sis;
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this.sos = sos;
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// In Tomcat, the order the listeners are set controls the order
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// that the first calls are made. In this case, the read listener
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// will be called before the write listener.
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sis.setReadListener(this);
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sos.setWriteListener(this);
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}
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@Override
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public void onDataAvailable() throws IOException {
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int read = 0;
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// Loop as long as there is data to read. If isReady() returns false
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// the socket will be added to the poller and onDataAvailable() will
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// be called again as soon as there is more data to read.
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while (sis.isReady() && read > -1) {
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read = sis.read(buffer);
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if (read > 0) {
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totalBytesRead += read;
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}
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}
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}
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@Override
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public void onAllDataRead() throws IOException {
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readFinished = true;
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// If sos is not ready to write data, the call to isReady() will
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// register the socket with the poller which will trigger a call to
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// onWritePossible() when the socket is ready to have data written
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// to it.
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if (sos.isReady()) {
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onWritePossible();
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}
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}
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@Override
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public void onWritePossible() throws IOException {
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if (readFinished) {
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// Must be ready to write data if onWritePossible was called
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String msg = "Total bytes written = [" + totalBytesRead + "]";
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sos.write(msg.getBytes(StandardCharsets.UTF_8));
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ac.complete();
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}
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}
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@Override
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public void onError(Throwable throwable) {
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// Should probably log the throwable
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ac.complete();
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}
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}
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}
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