解决Netty解码http请求获取URL乱码问题

为了解决Netty解码http请求获取URL乱码问题，我们需要：

1. 设置正确的字符集

在Netty中解析http请求时，如果没有指定字符集，Netty默认使用ISO-8859-1字符集进行解析。此时如果请求URL中含有中文等非ASCII字符，就会出现乱码问题。因此我们需要手动设置正确的字符集。

设置字符集的方法很简单，只需要在ChannelPipeline中添加一个ChannelInitializer，重写其initChannel方法，在其中添加一个HttpRequestDecoder并指定字符集即可，示例代码如下：

public class HttpServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new HttpRequestDecoder(Charset.forName("UTF-8")));
        pipeline.addLast(new HttpServerHandler());
    }
}

1. UrlDecoder解码

在网路传输过程中，URL被转码压缩，这个过程叫做URL编码。URL编码的结果是原始URL的一个字符串映射。URLDecoder类能够对这种映射进行反编码，还原出原始URL。因此我们需要在Netty中解码URL，示例代码如下：

public class HttpServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof FullHttpRequest) {
            FullHttpRequest request = (FullHttpRequest) msg;

            // 反编码URL
            String uri = URLDecoder.decode(request.uri(), "UTF-8");

            // 打印反编码后的URL
            System.out.println("Received URI: " + uri);

            // 处理请求

            FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
            response.content().writeBytes("Response body".getBytes());

            ctx.writeAndFlush(response);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

至此，我们已经解决了Netty解码http请求获取URL乱码问题。

示例1：

客户端发送的请求：

GET /%E4%B8%AD%E6%96%87 HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9

服务端打印的请求URI为：

Received URI: /中文

示例2：

客户端发送的请求：

GET /example/test%20abc HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9

服务端打印的请求URI为：

Received URI: /example/test abc