【Netty源码解读和权威指南】第42篇：Netty开发HTTP客户端——高并发请求轻松搞定

上一篇【第41篇】Netty开发HTTP服务——打造轻量级Web服务器 下一篇【第43篇】Netty WebSocket实战——轻松实现实时双向通信

一、HTTP客户端Pipeline

Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) {
ch.pipeline().addLast(new HttpClientCodec()); // 客户端编解码
ch.pipeline().addLast(new HttpObjectAggregator(65536));
ch.pipeline().addLast(new HttpClientHandler());
}
});

注：客户端使用HttpClientCodec，服务端使用HttpServerCodec。

二、异步HTTP客户端

public class AsyncHttpClient {
public static void get(EventLoopGroup group, String host, int port, String path) {
Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) {
ch.pipeline().addLast(new HttpClientCodec());
ch.pipeline().addLast(new HttpObjectAggregator(65536));
ch.pipeline().addLast(new ResponseHandler());
}
});

b.connect(host, port).addListener((ChannelFuture f) -> {
if (f.isSuccess()) {
FullHttpRequest req = new DefaultFullHttpRequest(HTTP_1_1, GET, path);
req.headers().set(HOST, host);
req.headers().set(CONNECTION, CLOSE);
f.channel().writeAndFlush(req);
}
});
}

static class ResponseHandler extends SimpleChannelInboundHandler<FullHttpResponse> {
protected void channelRead0(ChannelHandlerContext ctx, FullHttpResponse resp) {
System.out.println("Status: " + resp.status());
System.out.println("Body: " + resp.content().toString(UTF_8));
ctx.close();
}
}
}

三、连接池复用

// 建立Channel连接池，复用连接
public class HttpConnectionPool {
private final Bootstrap b;
private final Queue<Channel> pool = new ConcurrentLinkedQueue<>();

public Future<Channel> acquire(EventLoop executor) {
Channel ch = pool.poll();
if (ch != null && ch.isActive()) {
return executor.newSucceededFuture(ch);
}
return b.connect();
}

public void release(Channel ch) {
if (ch.isActive()) {
pool.offer(ch); // 归还连接
}
}
}

四、实现简单HTTP爬虫

public class SimpleCrawler {
public static void main(String[] args) throws Exception {
EventLoopGroup group = new NioEventLoopGroup(4);
List<String> urls = Arrays.asList(
"http://example.com/page1",
"http://example.com/page2",
"http://example.com/page3"
);

for (String url : urls) {
get(group, url); // 并发发送请求
}
Thread.sleep(5000);
group.shutdownGracefully();
}

public static void get(EventLoopGroup group, String url) {
URI uri = URI.create(url);
AsyncHttpClient.get(group, uri.getHost(),
uri.getPort() == –1 ? 80 : uri.getPort(), uri.getPath());
}
}

五、总结

上一篇【第41篇】Netty开发HTTP服务——打造轻量级Web服务器 下一篇【第43篇】Netty WebSocket实战——轻松实现实时双向通信