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Netty 是一个高性能的异步事件驱动的网络应用框架，用于快速开发可维护的高性能协议服务器和客户端。要使用 Netty 搭建一个支持 HTTP 方法（GET, POST, PUT, DELETE）的 HTTP 服务器，可以按照以下步骤进行操作。

准备工作

1. 添加依赖：确保你的项目中包含了 Netty 的相关依赖。
2. Java版本：确保你使用的 Java 版本支持 Netty，一般推荐使用 Java 8 或更高版本。

添加 Maven 依赖

在你的 pom.xml 文件中添加以下依赖：

<dependencies><dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.1.95.Final</version></dependency>
</dependencies>

创建 HTTP 服务器

下面是一个简单的示例，展示了如何创建一个支持 GET, POST, PUT, DELETE 方法的 HTTP 服务器。

1. 定义 HTTP 请求处理器

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;
import io.netty.util.CharsetUtil;public class HttpServerHandler extends SimpleChannelInboundHandler<FullHttpRequest> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest req) throws Exception {if (!req.decoderResult().isSuccess()) {sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.BAD_REQUEST));return;}// 根据请求类型处理switch (req.method()) {case GET:handleGet(ctx, req);break;case POST:handlePost(ctx, req);break;case PUT:handlePut(ctx, req);break;case DELETE:handleDelete(ctx, req);break;default:sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.METHOD_NOT_ALLOWED));break;}}private void handleGet(ChannelHandlerContext ctx, FullHttpRequest req) {// 处理 GET 请求FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("This is a GET response", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private void handlePost(ChannelHandlerContext ctx, FullHttpRequest req) {// 处理 POST 请求FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("This is a POST response", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private void handlePut(ChannelHandlerContext ctx, FullHttpRequest req) {// 处理 PUT 请求FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("This is a PUT response", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private void handleDelete(ChannelHandlerContext ctx, FullHttpRequest req) {// 处理 DELETE 请求FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("This is a DELETE response", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private static void sendHttpResponse(ChannelHandlerContext ctx, FullHttpRequest req, FullHttpResponse res) {if (res.status().code() != 200) {ByteBuf buf = Unpooled.copiedBuffer(res.status().toString(), CharsetUtil.UTF_8);res.content().writeBytes(buf);buf.release();HttpHeaders.setContentLength(res, res.content().readableBytes());}// Generate an error page if response status code is not 200 (OK).if (res.status().code() != 200) {ByteBuf buf = Unpooled.copiedBuffer(res.status().toString(), CharsetUtil.UTF_8);res.content().writeBytes(buf);buf.release();}// Send the response and close the connection if necessary.ChannelFuture f = ctx.channel().writeAndFlush(res);if (!HttpHeaders.isKeepAlive(req) || res.status().code() != 200) {f.addListener(ChannelFutureListener.CLOSE);}}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}
}

2. 启动服务器

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;public class HttpServer {public static void main(String[] args) throws InterruptedException {int port = 8080; // 选择一个端口EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new HttpServerInitializer());ChannelFuture f = b.bind(port).sync();System.out.println("HTTP server started on port " + port);f.channel().closeFuture().sync();} finally {bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();}}
}

3. 初始化 Channel

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;public class HttpServerInitializer extends ChannelInitializer<SocketChannel> {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ChannelPipeline p = ch.pipeline();p.addLast(new HttpResponseEncoder());p.addLast(new HttpRequestDecoder());p.addLast(new HttpObjectAggregator(65536));p.addLast(new HttpServerHandler());}
}

以上代码提供了一个基本的 HTTP 服务器框架，你可以根据需要添加具体的业务逻辑处理，如错误处理、日志记录、文件上传等高级功能。

在 Netty 中处理文件上传通常涉及到对 HTTP 请求中的 multipart/form-data 类型的解析。这种类型的请求通常用于上传文件和其他表单数据。下面介绍如何使用 Netty 和第三方库来处理文件上传。

第三方库

对于文件上传的支持，我们可以使用 netty-http2 项目中的 netty-codec-http2 依赖或者使用 netty-file-upload 项目中的 netty-codec-http 依赖，后者提供了更直接的方式来处理文件上传。我们将使用 netty-codec-http 依赖。

首先，在你的 pom.xml 文件中添加如下依赖：

<dependencies><dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.1.95.Final</version></dependency><dependency><groupId>io.netty</groupId><artifactId>netty-codec-http</artifactId><version>4.1.95.Final</version></dependency><dependency><groupId>commons-fileupload</groupId><artifactId>commons-fileupload</artifactId><version>1.4</version></dependency>
</dependencies>

文件上传处理

1. HTTP 请求解析器：使用 HttpDataFactory 和 HttpPostRequestDecoder 解析上传的数据。
2. 文件保存：定义一个方法来保存上传的文件。

更新 HttpServerHandler

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;
import io.netty.util.CharsetUtil;
import org.apache.commons.fileupload.FileItemIterator;
import org.apache.commons.fileupload.FileItemStream;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.fileupload.util.Streams;import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;public class HttpServerHandler extends SimpleChannelInboundHandler<FullHttpRequest> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest req) throws Exception {if (!req.decoderResult().isSuccess()) {sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.BAD_REQUEST));return;}switch (req.method()) {case GET:handleGet(ctx, req);break;case POST:handlePost(ctx, req);break;case PUT:handlePut(ctx, req);break;case DELETE:handleDelete(ctx, req);break;default:sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.METHOD_NOT_ALLOWED));break;}}private void handlePost(ChannelHandlerContext ctx, FullHttpRequest req) {if (!req.headers().contains(HttpHeaderNames.CONTENT_TYPE)) {sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.BAD_REQUEST));return;}String contentType = req.headers().get(HttpHeaderNames.CONTENT_TYPE);if (contentType.contains("multipart/form-data")) {handleFileUpload(ctx, req);} else {handleRegularPost(ctx, req);}}private void handleFileUpload(ChannelHandlerContext ctx, FullHttpRequest req) {FileUpload fileUpload = new FileUpload(new DiskFileItemFactory());HttpPostRequestDecoder decoder = new HttpPostRequestDecoder(fileUpload, req);while (true) {try {HttpPostRequestDecoder.State state = decoder.decode(ctx.channel(), req, ctx.alloc().buffer());if (state == HttpPostRequestDecoder.State.END_OF_MESSAGE) {break;}if (state == HttpPostRequestDecoder.State.CHUNKED_INPUT) {decoder.offer(req);}} catch (HttpPostRequestDecoder.EndOfDataDecoderException e) {break;} catch (HttpPostRequestDecoder.ErrorDataDecoderException e) {sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.BAD_REQUEST));return;}}FileItemIterator iterator = decoder.getBodyHttpData();while (iterator.hasNext()) {FileItemStream item = iterator.next();if (item.isFormField()) {// Handle form fields here} else {saveUploadedFile(item, "/tmp/uploaded"); // Save the file to disk}}FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("File uploaded successfully.", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private void saveUploadedFile(FileItemStream item, String uploadDir) throws IOException {Path targetPath = Path.of(uploadDir, item.getName());Files.createDirectories(targetPath.getParent());try (FileItemStream.ItemStream stream = item.openStream()) {Files.copy(stream, targetPath, StandardCopyOption.REPLACE_EXISTING);}}private void handleRegularPost(ChannelHandlerContext ctx, FullHttpRequest req) {// Handle regular POST data hereFullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK,Unpooled.copiedBuffer("This is a POST response", CharsetUtil.UTF_8));sendHttpResponse(ctx, req, response);}private static void sendHttpResponse(ChannelHandlerContext ctx, FullHttpRequest req, FullHttpResponse res) {// ... [same as before]}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}
}

注意事项

• 在这个示例中，我们使用了 commons-fileupload 库来处理 multipart/form-data 数据。
• 上传的文件被保存到 /tmp/uploaded 目录下。你需要确保这个目录存在并且有适当的权限。
• 我们使用了 DiskFileItemFactory 和 FileUpload 来处理文件上传。
• 如果上传的文件非常大，你可能需要调整 DiskFileItemFactory 的配置以适应你的需求。

以上代码提供了一个基本的文件上传处理机制。你可以根据实际需要进一步扩展和优化。例如，可以添加文件大小限制、文件类型检查等功能。