实例：如何使用Netty下载文件

素颜马尾好姑娘i 2022-04-11 09:12 520阅读 0赞

使用场景：客户端向Netty请求一个文件，Netty服务端下载指定位置文件到客户端。

本实例使用的是Http协议，当然，可以通过简单的修改即可换成TCP协议。

需要注意本实例的关键点是，为了更高效的传输大数据，实例中用到了ChunkedWriteHandler编码器，它提供了以zero-memory-copy方式写文件。

第一步：先写一个HttpFileServer

package com.bijian.netty.server;
    
    import io.netty.bootstrap.ServerBootstrap;
    import io.netty.channel.Channel;
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelPipeline;
    import io.netty.channel.EventLoopGroup;
    import io.netty.channel.nio.NioEventLoopGroup;
    import io.netty.channel.socket.SocketChannel;
    import io.netty.channel.socket.nio.NioServerSocketChannel;
    import io.netty.handler.codec.http.HttpObjectAggregator;
    import io.netty.handler.codec.http.HttpServerCodec;
    import io.netty.handler.logging.LogLevel;
    import io.netty.handler.logging.LoggingHandler;
    import io.netty.handler.stream.ChunkedWriteHandler;
    
    public class HttpFileServer {
        
        static final int PORT = 8080;
    
        public static void main(String[] args) throws Exception {
            
            EventLoopGroup bossGroup = new NioEventLoopGroup(1);
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            try {
                ServerBootstrap b = new ServerBootstrap();
                b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                        .handler(new LoggingHandler(LogLevel.INFO)).childHandler(new ChannelInitializer<SocketChannel>() {// 有连接到达时会创建一个channel
                                    @Override
                                    protected void initChannel(SocketChannel ch) throws Exception {
                                        ChannelPipeline pipeline = ch.pipeline();
                                        pipeline.addLast(new HttpServerCodec());
                                        pipeline.addLast(new HttpObjectAggregator(65536));
                                        pipeline.addLast(new ChunkedWriteHandler());
                                        pipeline.addLast(new FileServerHandler());
                                    }
                                });
    
                Channel ch = b.bind(PORT).sync().channel();
                System.err.println("打开浏览器，输入： " + ("http") + "://127.0.0.1:" + PORT + '/');
                ch.closeFuture().sync();
            } finally {
                bossGroup.shutdownGracefully();
                workerGroup.shutdownGracefully();
            }
        }
    }

第二步：再写一个FileServerHandler

package com.bijian.netty.server;
    
    import static io.netty.handler.codec.http.HttpHeaders.Names.CACHE_CONTROL;
    import static io.netty.handler.codec.http.HttpHeaders.Names.CONTENT_TYPE;
    import static io.netty.handler.codec.http.HttpHeaders.Names.DATE;
    import static io.netty.handler.codec.http.HttpHeaders.Names.EXPIRES;
    import static io.netty.handler.codec.http.HttpHeaders.Names.IF_MODIFIED_SINCE;
    import static io.netty.handler.codec.http.HttpHeaders.Names.LAST_MODIFIED;
    import static io.netty.handler.codec.http.HttpHeaders.Names.LOCATION;
    import static io.netty.handler.codec.http.HttpResponseStatus.BAD_REQUEST;
    import static io.netty.handler.codec.http.HttpResponseStatus.FORBIDDEN;
    import static io.netty.handler.codec.http.HttpResponseStatus.FOUND;
    import static io.netty.handler.codec.http.HttpResponseStatus.INTERNAL_SERVER_ERROR;
    import static io.netty.handler.codec.http.HttpResponseStatus.NOT_FOUND;
    import static io.netty.handler.codec.http.HttpResponseStatus.NOT_MODIFIED;
    import static io.netty.handler.codec.http.HttpResponseStatus.OK;
    import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
    import io.netty.buffer.ByteBuf;
    import io.netty.buffer.Unpooled;
    import io.netty.channel.ChannelFuture;
    import io.netty.channel.ChannelFutureListener;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelProgressiveFuture;
    import io.netty.channel.ChannelProgressiveFutureListener;
    import io.netty.channel.DefaultFileRegion;
    import io.netty.channel.SimpleChannelInboundHandler;
    import io.netty.handler.codec.http.DefaultFullHttpResponse;
    import io.netty.handler.codec.http.DefaultHttpResponse;
    import io.netty.handler.codec.http.FullHttpRequest;
    import io.netty.handler.codec.http.FullHttpResponse;
    import io.netty.handler.codec.http.HttpChunkedInput;
    import io.netty.handler.codec.http.HttpHeaders;
    import io.netty.handler.codec.http.HttpResponse;
    import io.netty.handler.codec.http.HttpResponseStatus;
    import io.netty.handler.codec.http.HttpVersion;
    import io.netty.handler.codec.http.LastHttpContent;
    import io.netty.handler.ssl.SslHandler;
    import io.netty.handler.stream.ChunkedFile;
    import io.netty.util.CharsetUtil;
    import io.netty.util.internal.SystemPropertyUtil;
    
    import java.io.File;
    import java.io.FileNotFoundException;
    import java.io.RandomAccessFile;
    import java.io.UnsupportedEncodingException;
    import java.net.URLDecoder;
    import java.text.SimpleDateFormat;
    import java.util.Calendar;
    import java.util.Date;
    import java.util.GregorianCalendar;
    import java.util.Locale;
    import java.util.TimeZone;
    import java.util.regex.Pattern;
    
    import javax.activation.MimetypesFileTypeMap;
    
    public class FileServerHandler extends SimpleChannelInboundHandler<FullHttpRequest> {
        
        public static final String HTTP_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss zzz";
        public static final String HTTP_DATE_GMT_TIMEZONE = "GMT";
        public static final int HTTP_CACHE_SECONDS = 60;
    
        @Override
        protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) throws Exception {
            
            // 监测解码情况
            if (!request.getDecoderResult().isSuccess()) {
                sendError(ctx, BAD_REQUEST);
                return;
            }
            final String uri = request.getUri();
            final String path = sanitizeUri(uri);
            if (path == null) {
                sendError(ctx, FORBIDDEN);
                return;
            }
            //读取要下载的文件
            File file = new File(path);
            if (file.isHidden() || !file.exists()) {
                sendError(ctx, NOT_FOUND);
                return;
            }
            if (file.isDirectory()) {
                if (uri.endsWith("/")) {
                    sendListing(ctx, file);
                } else {
                    sendRedirect(ctx, uri + '/');
                }
                return;
            }
            if (!file.isFile()) {
                sendError(ctx, FORBIDDEN);
                return;
            }
            // Cache Validation
            String ifModifiedSince = request.headers().get(IF_MODIFIED_SINCE);
            if (ifModifiedSince != null && !ifModifiedSince.isEmpty()) {
                SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
                Date ifModifiedSinceDate = dateFormatter.parse(ifModifiedSince);
                // Only compare up to the second because the datetime format we send
                // to the client
                // does not have milliseconds
                long ifModifiedSinceDateSeconds = ifModifiedSinceDate.getTime() / 1000;
                long fileLastModifiedSeconds = file.lastModified() / 1000;
                if (ifModifiedSinceDateSeconds == fileLastModifiedSeconds) {
                    sendNotModified(ctx);
                    return;
                }
            }
            RandomAccessFile raf;
            try {
                raf = new RandomAccessFile(file, "r");
            } catch (FileNotFoundException ignore) {
                sendError(ctx, NOT_FOUND);
                return;
            }
            long fileLength = raf.length();
            HttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
            HttpHeaders.setContentLength(response, fileLength);
            setContentTypeHeader(response, file);
            setDateAndCacheHeaders(response, file);
            if (HttpHeaders.isKeepAlive(request)) {
                response.headers().set("CONNECTION", HttpHeaders.Values.KEEP_ALIVE);
            }
    
            // Write the initial line and the header.
            ctx.write(response);
    
            // Write the content.
            ChannelFuture sendFileFuture;
            if (ctx.pipeline().get(SslHandler.class) == null) {
                sendFileFuture = ctx.write(new DefaultFileRegion(raf.getChannel(), 0, fileLength),
                        ctx.newProgressivePromise());
            } else {
                sendFileFuture = ctx.write(new HttpChunkedInput(new ChunkedFile(raf, 0, fileLength, 8192)),
                        ctx.newProgressivePromise());
            }
            sendFileFuture.addListener(new ChannelProgressiveFutureListener() {
                @Override
                public void operationProgressed(ChannelProgressiveFuture future, long progress, long total) {
                    if (total < 0) { // total unknown
                        System.err.println(future.channel() + " Transfer progress: " + progress);
                    } else {
                        System.err.println(future.channel() + " Transfer progress: " + progress + " / " + total);
                    }
                }
    
                @Override
                public void operationComplete(ChannelProgressiveFuture future) {
                    System.err.println(future.channel() + " Transfer complete.");
                }
            });
    
            // Write the end marker
            ChannelFuture lastContentFuture = ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
    
            // Decide whether to close the connection or not.
            if (!HttpHeaders.isKeepAlive(request)) {
                // Close the connection when the whole content is written out.
                lastContentFuture.addListener(ChannelFutureListener.CLOSE);
            }
        }
    
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
            cause.printStackTrace();
            if (ctx.channel().isActive()) {
                sendError(ctx, INTERNAL_SERVER_ERROR);
            }
        }
    
        private static final Pattern INSECURE_URI = Pattern.compile(".*[<>&\"].*");
    
        private static String sanitizeUri(String uri) {
            // Decode the path.
            try {
                uri = URLDecoder.decode(uri, "UTF-8");
            } catch (UnsupportedEncodingException e) {
                throw new Error(e);
            }
    
            if (!uri.startsWith("/")) {
                return null;
            }
    
            // Convert file separators.
            uri = uri.replace('/', File.separatorChar);
    
            // Simplistic dumb security check.
            // You will have to do something serious in the production environment.
            if (uri.contains(File.separator + '.') || uri.contains('.' + File.separator) || uri.startsWith(".")
                    || uri.endsWith(".") || INSECURE_URI.matcher(uri).matches()) {
                return null;
            }
    
            // Convert to absolute path.
            return SystemPropertyUtil.get("user.dir") + File.separator + uri;
        }
    
        private static final Pattern ALLOWED_FILE_NAME = Pattern.compile("[A-Za-z0-9][-_A-Za-z0-9\\.]*");
    
        private static void sendListing(ChannelHandlerContext ctx, File dir) {
            FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK);
            response.headers().set(CONTENT_TYPE, "text/html; charset=UTF-8");
    
            StringBuilder buf = new StringBuilder();
            String dirPath = dir.getPath();
    
            buf.append("<!DOCTYPE html>\r\n");
            buf.append("<html><head><title>");
            buf.append("Listing of: ");
            buf.append(dirPath);
            buf.append("</title></head><body>\r\n");
    
            buf.append("<h3>Listing of: ");
            buf.append(dirPath);
            buf.append("</h3>\r\n");
    
            buf.append("<ul>");
            buf.append("<li><a href=\"../\">..</a></li>\r\n");
    
            for (File f : dir.listFiles()) {
                if (f.isHidden() || !f.canRead()) {
                    continue;
                }
    
                String name = f.getName();
                if (!ALLOWED_FILE_NAME.matcher(name).matches()) {
                    continue;
                }
    
                buf.append("<li><a href=\"");
                buf.append(name);
                buf.append("\">");
                buf.append(name);
                buf.append("</a></li>\r\n");
            }
    
            buf.append("</ul></body></html>\r\n");
            ByteBuf buffer = Unpooled.copiedBuffer(buf, CharsetUtil.UTF_8);
            response.content().writeBytes(buffer);
            buffer.release();
    
            // Close the connection as soon as the error message is sent.
            ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        }
    
        private static void sendRedirect(ChannelHandlerContext ctx, String newUri) {
            FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, FOUND);
            response.headers().set(LOCATION, newUri);
    
            // Close the connection as soon as the error message is sent.
            ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        }
    
        private static void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
            FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, status, Unpooled.copiedBuffer("Failure: "
                    + status + "\r\n", CharsetUtil.UTF_8));
            response.headers().set(CONTENT_TYPE, "text/plain; charset=UTF-8");
    
            // Close the connection as soon as the error message is sent.
            ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        }
    
        /**
         * When file timestamp is the same as what the browser is sending up, send a
         * "304 Not Modified"
         * 
         * @param ctx
         *            Context
         */
        private static void sendNotModified(ChannelHandlerContext ctx) {
            FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, NOT_MODIFIED);
            setDateHeader(response);
    
            // Close the connection as soon as the error message is sent.
            ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        }
    
        /**
         * Sets the Date header for the HTTP response
         * 
         * @param response
         *            HTTP response
         */
        private static void setDateHeader(FullHttpResponse response) {
            SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
            dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));
    
            Calendar time = new GregorianCalendar();
            response.headers().set(DATE, dateFormatter.format(time.getTime()));
        }
    
        /**
         * Sets the Date and Cache headers for the HTTP Response
         * 
         * @param response
         *            HTTP response
         * @param fileToCache
         *            file to extract content type
         */
        private static void setDateAndCacheHeaders(HttpResponse response, File fileToCache) {
            SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
            dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));
    
            // Date header
            Calendar time = new GregorianCalendar();
            response.headers().set(DATE, dateFormatter.format(time.getTime()));
    
            // Add cache headers
            time.add(Calendar.SECOND, HTTP_CACHE_SECONDS);
            response.headers().set(EXPIRES, dateFormatter.format(time.getTime()));
            response.headers().set(CACHE_CONTROL, "private, max-age=" + HTTP_CACHE_SECONDS);
            response.headers().set(LAST_MODIFIED, dateFormatter.format(new Date(fileToCache.lastModified())));
        }
    
        /**
         * Sets the content type header for the HTTP Response
         * 
         * @param response
         *            HTTP response
         * @param file
         *            file to extract content type
         */
        private static void setContentTypeHeader(HttpResponse response, File file) {
            MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
            response.headers().set(CONTENT_TYPE, mimeTypesMap.getContentType(file.getPath()));
        }
    }

第三步：启动Netty服务，在浏览器中输入http://127.0.0.1:8080/，如图所示：

![5430d566-1e55-358f-a24c-02b463c5a5cb.png][]  
        即可在浏览器中看到工程目录下所有文件，点击即可下载

ps:通过对本例进行简单修改可实现各种方式的文件下载

文章来源：[http://blog.csdn.net/suifeng3051/article/details/38679507][http_blog.csdn.net_suifeng3051_article_details_38679507]

[5430d566-1e55-358f-a24c-02b463c5a5cb.png]: /images/20220411/9872b5428ed54951a244dd4cfaafeaab.png
[http_blog.csdn.net_suifeng3051_article_details_38679507]: http://blog.csdn.net/suifeng3051/article/details/38679507