一、Netty应用场景

讲了一些Netty的组件，来聊一聊大家最关心的事情吧，他能够做什么？毕竟，我们学习就是拿来用的嘛。我可以简单的概括一下，凡是牵扯到网络相关的，都可以使用Neety去实现！

构建高性能、低时延的各种 Java 中间件，例如 MQ、分布式服务框架、ESB 消息总线等，Netty 主要作为基础通信框架提供高性能、低时延的通信服务；公有或者私有协议栈的基础通信框架，例如可以基于 Netty 构建异步、高性能的 WebSocket 协议栈；
各领域应用，例如大数据、游戏等，Netty 作为高性能的通信框架用于内部各模块的数据分发、传输和汇总等，实现模块之间高性能通信。
接下来的几篇，会围绕Netty实现相关功能进行展开。

二、Netty实现文件的上传和下载

1、MultipartRequest

import io.netty.handler.codec.http.multipart.FileUpload;
import org.json.simple.JSONObject;
import java.util.Map;
/**
 * <p>请求对象</p>
 *
 * @author DarkKing 
 */
public class MultipartRequest {
    private Map<String, FileUpload> fileUploads;
    private JSONObject params;
    public Map<String, FileUpload> getFileUploads() {
        return fileUploads;
    }
    public void setFileUploads(Map<String, FileUpload> fileUploads) {
        this.fileUploads = fileUploads;
    }
    public JSONObject getParams() {
        return params;
    }
    public void setParams(JSONObject params) {
        this.params = params;
    }
}

定义了一个http封装的对象。保存对应的传参数。

2、FileServer

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import java.net.InetSocketAddress;
/**
 * 作者：DarkKIng
 * 创建日期：2019/12/17
 * 类说明：文件下载服务端
 */
public class FileServer {
    private final int port;
    public FileServer(int port) {
        this.port = port;
    }
    public static void main(String[] args) throws InterruptedException {
        int port = 9999;
        FileServer fileServer = new FileServer(port);
        System.out.println("服务器即将启动");
        fileServer.start();
        System.out.println("服务器关闭");
    }
    public void start() throws InterruptedException {
        final FileServerHandle serverHandler = new FileServerHandle();
        /*线程组*/
        EventLoopGroup group = new NioEventLoopGroup();
        Pipeline pipeline = new Pipeline();
        try {
            /*服务端启动必须*/
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)/*将线程组传入*/
                    .channel(NioServerSocketChannel.class)/*指定使用NIO进行网络传输*/
                    .localAddress(new InetSocketAddress(port))/*指定服务器监听端口*/
                    /*服务端每接收到一个连接请求，就会新启一个socket通信，也就是channel，
                    所以下面这段代码的作用就是为这个子channel增加handle*/
                    .childHandler(pipeline);
            ChannelFuture f = b.bind().sync();/*异步绑定到服务器，sync()会阻塞直到完成*/
            System.out.println("Netty server  start,port is " + port);
            f.channel().closeFuture().sync();/*阻塞直到服务器的channel关闭*/
        } finally {
            group.shutdownGracefully().sync();/*优雅关闭线程组*/
        }
    }
}

使用netty实现服文件服务器端。

3、Pipeline

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpRequestDecoder;
import io.netty.handler.codec.http.HttpResponseEncoder;
import io.netty.util.concurrent.DefaultEventExecutorGroup;
import io.netty.util.concurrent.EventExecutorGroup;
/**
 * 作者：DarkKIng
 * 创建日期：2019/12/17
 * 作用：职责链
 */
public class Pipeline extends ChannelInitializer<SocketChannel> {
    private EventExecutorGroup businessEventExecutorGroup = new DefaultEventExecutorGroup(10);
    @Override
    protected void initChannel(SocketChannel ch) {
        ChannelPipeline pipeline = ch.pipeline();
        /**
         * http服务器端对response编码
         */
        pipeline.addLast("encoder", new HttpResponseEncoder());
        /**
         * http服务器端对request解码3.
         */
        pipeline.addLast("decoder", new HttpRequestDecoder());
        /**
         * 合并请求
         */
        pipeline.addLast("aggregator", new HttpObjectAggregator(655300000));
        /**
         * 正常业务逻辑处理
         */
        pipeline.addLast(businessEventExecutorGroup, new FileServerHandle());
    }
}

编写职责链，请求会从入栈以次从上到下经过编解码，请求和秉承HTTPObject，最后执行业务类FileServerHandle。

4、FileServerHandle

import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.handler.codec.http.*;
import io.netty.handler.codec.http.multipart.*;
import io.netty.util.CharsetUtil;
import org.json.simple.JSONObject;
import java.io.*;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
/**
 * 作者：DarkKIng
 * 创建日期：2019/12/17
 * 类说明：文件下载handler
 */
@Sharable
public class FileServerHandle extends SimpleChannelInboundHandler<FullHttpRequest> {
    /*客户端读到数据以后，就会执行*/
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request)
            throws Exception {
        //打印请求url
        System.out.println(request.uri());
        //下载任务处理
        if (request.uri().equals("/downFile")) {
            responseExportFile(ctx, "D://model.txt", "model.txt");
        }
        //上传接口处理
        if (request.uri().equals("/upLoadFile")) {
            MultipartRequest MultipartBody = getMultipartBody(request);
            Map<String, FileUpload> fileUploads = MultipartBody.getFileUploads();
            //输出文件信息
            for (String key : fileUploads.keySet()) {
                //获取文件对象
                FileUpload file = fileUploads.get(key);
                System.out.println("fileName is" + file.getFile().getPath());
                //获取文件流
                InputStream in = new FileInputStream(file.getFile());
                BufferedReader bf = new BufferedReader(new InputStreamReader(in));
                String content = bf.lines().collect(Collectors.joining("\n"));
                //打印文件
                System.out.println("content is \n" + content);
            }
            //输出参数信息
            JSONObject params = MultipartBody.getParams();
            //输出文件信息
            System.out.println(JSONObject.toJSONString(params));
        }
    }
    /*连接建立以后*/
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.copiedBuffer(
                "Hello Netty", CharsetUtil.UTF_8));
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
    /**
     * <p>
     * 返回下载内容
     * </p>
     *
     * @param ctx
     * @author DarkKing 2019-12-17
     */
    public static void responseExportFile(ChannelHandlerContext ctx, String path, String name) {
        File file = new File(path);
        try {
            //随机读取文件
            final RandomAccessFile raf = new RandomAccessFile(file, "r");
            long fileLength = raf.length();
            //定义response对象
            HttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
            //设置请求头部
            response.headers().set(HttpHeaderNames.CONTENT_LENGTH, fileLength);
            response.headers().set(HttpHeaderNames.CONTENT_TYPE, "application/octet-stream; charset=UTF-8");
            response.headers().add(HttpHeaderNames.CONTENT_DISPOSITION,
                    "attachment; filename=\"" + URLEncoder.encode(file.getName(), "UTF-8") + "\";");
            ctx.write(response);
            //设置事件通知对象
            ChannelFuture sendFileFuture = ctx
                    .write(new DefaultFileRegion(raf.getChannel(), 0, fileLength), ctx.newProgressivePromise());
            sendFileFuture.addListener(new ChannelProgressiveFutureListener() {
                //文件传输完成执行监听器
                @Override
                public void operationComplete(ChannelProgressiveFuture future)
                        throws Exception {
                    System.out.println("file {} transfer complete.");
                }
                //文件传输进度监听器
                @Override
                public void operationProgressed(ChannelProgressiveFuture future,
                                                long progress, long total) throws Exception {
                    if (total < 0) {
                        System.out.println("file {} transfer progress: {}");
                    } else {
                        System.out.println("file {} transfer progress: {}/{}");
                    }
                }
            });
            //刷新缓冲区数据，文件结束标志符
            ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * 功能描述
     * <p>解析文件上传</p>
     *
     * @author DarkKing 2019/10/9 15:24
     * @params [ctx, httpDecode]
     */
    private static MultipartRequest getMultipartBody(FullHttpRequest request) {
        try {
            //创建HTTP对象工厂
            HttpDataFactory factory = new DefaultHttpDataFactory(true);
            //使用HTTP POST解码器
            HttpPostRequestDecoder httpDecoder = new HttpPostRequestDecoder(factory, request);
            httpDecoder.setDiscardThreshold(0);
            if (httpDecoder != null) {
                //获取HTTP请求对象
                final HttpContent chunk = (HttpContent) request;
                //加载对象到加吗器。
                httpDecoder.offer(chunk);
                if (chunk instanceof LastHttpContent) {
                    //自定义对象bean
                    MultipartRequest multipartRequest = new MultipartRequest();
                    //存放文件对象
                    Map<String, FileUpload> fileUploads = new HashMap<>();
                    //存放参数对象
                    JSONObject body = new JSONObject();
                    //通过迭代器获取HTTP的内容
                    java.util.List<InterfaceHttpData> InterfaceHttpDataList = httpDecoder.getBodyHttpDatas();
                    for (InterfaceHttpData data : InterfaceHttpDataList) {
                        //如果数据类型为文件类型，则保存到fileUploads对象中
                        if (data != null && InterfaceHttpData.HttpDataType.FileUpload.equals(data.getHttpDataType())) {
                            FileUpload fileUpload = (FileUpload) data;
                            fileUploads.put(data.getName(), fileUpload);
                        }
                        //如果数据类型为参数类型，则保存到body对象中
                        if (data.getHttpDataType() == InterfaceHttpData.HttpDataType.Attribute) {
                            Attribute attribute = (Attribute) data;
                            body.put(attribute.getName(), attribute.getValue());
                        }
                    }
                    //存放文件信息
                    multipartRequest.setFileUploads(fileUploads);
                    //存放参数信息
                    multipartRequest.setParams(body);
                    return multipartRequest;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}