实例：怎样使用 Netty 下载文件

本实例主要參考的是官网的examples：点击这里

使用场景：client向Netty请求一个文件，Netty服务端下载指定位置文件到client。

本实例使用的是Http协议，当然，能够通过简单的改动就可以换成TCP协议。

须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: <a
* href=mailto:wanghouda@126.com>wanghouda</a>
* @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<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();
}
}
}

</pre><pre>

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:
* <href=mailto:wanghouda@126.com>wanghouda</a>
*
* @Title: HttpFileServerHandler.java
* @Package NettyDemo.file.server Description: Version: 1.0
******************************************************************************/
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 {
// 监測解码情况
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>rn");
buf.append("<html><head><title>");
buf.append("Listing of: ");
buf.append(dirPath);
buf.append("</title></head><body>rn");
buf.append("<h3>Listing of: ");
buf.append(dirPath);
buf.append("</h3>rn");
buf.append("<ul>");
buf.append("<li><a href="../">..</a></li>rn");
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>rn");
}
buf.append("</ul></body></html>rn");
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 + "rn", 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/

     如图所看到的：就可以在浏览器中看到project文件夹下全部文件，点击就可以下载

    

ps:通过对本例进行简单改动可实现各种方式的文件下载