如何使用 Netty 下载文件

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 NettyDemo.file.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;

 /*******************************************************************************
  * Reserved. BidPlanStructForm.java Created on 2014-8-19 Author:
  * href=mailto:[email protected]>wanghouda
  * @Title: HttpFileServer.java
  * @Package NettyDemo.file.server Description: Version: 1.0
  ******************************************************************************/
 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() {// 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 NettyDemo.file.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;

 /*******************************************************************************
  * Created on 2014-8-19 Author:
  * wanghouda
  *
  * @Title: HttpFileServerHandler.java
  * @Package NettyDemo.file.server Description: Version: 1.0
  ******************************************************************************/
 public class FileServerHandler extends SimpleChannelInboundHandler {
     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("\r\n");
         buf.append(""</span><span style="margin:0px; padding:0px; border:none; background-color:inherit">);  </span></span></li> 
    <li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"> <span style="margin:0px; padding:0px; border:none; color:black; background-color:inherit">        buf.append(<span class="string" style="margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"Listing of: "</span><span style="margin:0px; padding:0px; border:none; background-color:inherit">);  </span></span></li> 
    <li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important"> <span style="margin:0px; padding:0px; border:none; color:black; background-color:inherit">        buf.append(dirPath);  </span></li> 
    <li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"> <span style="margin:0px; padding:0px; border:none; color:black; background-color:inherit">        buf.append(<span class="string" style="margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"\r\n");

         buf.append("Listing of: ");
         buf.append(dirPath);
         buf.append("\r\n");

         buf.append("");   
             buf.append("..\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(");   
                 buf.append(name);   
                 buf.append("\">");   
                 buf.append(name);   
                 buf.append("\r\n");   
             }   
        
             buf.append("\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：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