checgg

@Aruforce @zhuyichen1017

https://github.com/netty/netty/tree/4.1/example/src/main/java/io/netty/example/http/helloworld

65-69 行:

```
/*
* Copyright 2013 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.example.http.helloworld;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpObject;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpUtil;

import static io.netty.handler.codec.http.HttpHeaderNames.CONNECTION;
import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;
import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_TYPE;
import static io.netty.handler.codec.http.HttpHeaderValues.CLOSE;
import static io.netty.handler.codec.http.HttpHeaderValues.KEEP_ALIVE;
import static io.netty.handler.codec.http.HttpHeaderValues.TEXT_PLAIN;
import static io.netty.handler.codec.http.HttpResponseStatus.OK;

public class HttpHelloWorldServerHandler extends SimpleChannelInboundHandler<HttpObject> {
private static final byte[] COnTENT= { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd' };

@Override
public void channelReadComplete(ChannelHandlerContext ctx) {
ctx.flush();
}

@Override
public void channelRead0(ChannelHandlerContext ctx, HttpObject msg) {
if (msg instanceof HttpRequest) {
HttpRequest req = (HttpRequest) msg;

boolean keepAlive = HttpUtil.isKeepAlive(req);
FullHttpResponse respOnse= new DefaultFullHttpResponse(req.protocolVersion(), OK,
Unpooled.wrappedBuffer(CONTENT));
response.headers()
.set(CONTENT_TYPE, TEXT_PLAIN)
.setInt(CONTENT_LENGTH, response.content().readableBytes());

if (keepAlive) {
if (!req.protocolVersion().isKeepAliveDefault()) {
response.headers().set(CONNECTION, KEEP_ALIVE);
}
} else {
// Tell the client we're going to close the connection.
response.headers().set(CONNECTION, CLOSE);
}
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
ChannelFuture f = ctx.write(response);

if (!keepAlive) {
f.addListener(ChannelFutureListener.CLOSE);
}
}
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}

```

一位常年潜水的个人开发者，没有任何广告哈~~
写了一些本人的一点沉淀和思考。

这个问题的实际需求是什么？
1 防止提交两次？
这只能客户端去解决。

2 防止数据入库两次？
那么重复提交的定义是什么？
两个客户端，提交同一份数据，算重复提交吗？
如果算，设置数据库唯一索引就好，写入相同数据会失败。
如果不算，服务端没法验证。因为客户端请求都可以伪造。

这是啥问题？
并行和并发的定义是啥，不理解，能否补充一下英文关键词或者具体业务场景？
大量 IO 是指的磁盘 IO 还是网络 IO ？