java - 使用 Netty 的异步 HTTP 客户端

Question

我是 netty 的新手，仍在努力寻找自己的出路。我正在寻找创建一个异步工作的 http 客户端。http的netty例子只展示了如何等待IO操作，没有展示如何使用addListener，所以这几天一直在想办法。

我正在尝试创建一个请求类来处理请求的所有不同状态，从连接、发送数据、处理响应到关闭连接。为此，我的类扩展了 SimpleChannelUpstreamHandler 并实现了 ChannelFutureListener。我使用 ChannelPipelineFactory 将类(作为 SimpleChannelUpstreamHandler)的(this)实例作为处理程序添加到管道中。

连接是这样创建的:

this.state = State.Connecting;
this.clientBootstrap.connect(this.address).addListener(this);

然后是operationComplete方法:

@Override
public void operationComplete(ChannelFuture future) throws Exception {
    State oldState = this.state;

    if (!future.isSuccess()) {
        this.status = Status.Failed;
        future.getChannel().disconnect().addListener(this);
    }
    else if (future.isCancelled()) {
        this.status = Status.Canceled;
        future.getChannel().disconnect().addListener(this);
    }
    else switch (this.state) {
        case Connecting:
            this.state = State.Sending;
            Channel channel = future.getChannel();
            channel.write(this.createRequest()).addListener(this);
            break;

        case Sending:
            this.state = State.Disconnecting;
            future.getChannel().disconnect().addListener(this);
            break;

        case Disconnecting:
            this.state = State.Closing;
            future.getChannel().close().addListener(this);
            break;

        case Closing:
            this.state = State.Finished;
            break;
    }
    System.out.println("request operationComplete start state: " + oldState + ", end state: " + this.state + ", status: " + this.status);
}

private HttpRequest createRequest() {
    String url = this.url.toString();

    HttpRequest request = new DefaultHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, url);
    request.setHeader(HttpHeaders.Names.HOST, this.url.getHost());
    request.setHeader(HttpHeaders.Names.CONNECTION, HttpHeaders.Values.CLOSE);
    request.setHeader(HttpHeaders.Names.ACCEPT_ENCODING, HttpHeaders.Values.GZIP);

    return request;
}

该类还覆盖了messageReceived 方法:

@Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
    System.out.println("messageReceived");
    HttpResponse response = (HttpResponse) e.getMessage();

    ChannelBuffer content = response.getContent();
    if (content.readable()) {
        System.out.println("CONTENT: " + content.toString(CharsetUtil.UTF_8));
    }
}

问题是我得到了这个输出:

request operationComplete start state: Connecting, end state: Sending, status: Unknown
request operationComplete start state: Sending, end state: Disconnecting, status: Unknown
request operationComplete start state: Closing, end state: Finished, status: Unknown
request operationComplete start state: Disconnecting, end state: Finished, status: Unknown

如您所见，messageReceived 由于某种原因未被执行，即使管道工厂将此类的实例添加到管道。

知道我在这里遗漏了什么吗？谢谢。

---

编辑

感谢@JestanNirojan 的帮助，我终于成功了，以防有人对解决方案感兴趣:

public class ClientRequest extends SimpleChannelUpstreamHandler {

    ....

    public void connect() {
        this.state = State.Connecting;
        System.out.println(this.state);
        this.clientBootstrap.connect(this.address);
    }

    @Override
    public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        this.state = State.Sending;
        System.out.println(this.state);
        ctx.getChannel().write(this.createRequest());
    }

    @Override
    public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
        HttpResponse response = (HttpResponse) e.getMessage();

        ChannelBuffer content = response.getContent();
        if (content.readable()) {
            System.out.println("CONTENT: " + content.toString(CharsetUtil.UTF_8));
        }

        this.state = State.Disconnecting;
        System.out.println(this.state);
    }

    @Override
    public void channelDisconnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        this.state = State.Closing;
        System.out.println(this.state);
    }

    @Override
    public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        this.state = State.Finished;
        System.out.println(this.state);
    }

    private HttpRequest createRequest() {
        String url = this.url.toString();

        HttpRequest request = new DefaultHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, url);
        request.setHeader(HttpHeaders.Names.HOST, this.url.getHost());
        request.setHeader(HttpHeaders.Names.CONNECTION, HttpHeaders.Values.CLOSE);
        request.setHeader(HttpHeaders.Names.ACCEPT_ENCODING, HttpHeaders.Values.GZIP);

        return request;
    }
}

Answer 1

您正在使用 ChannelFutureListener 来执行 channel 中的所有操作(这很糟糕)， future 的监听器将在调用这些 channel 操作后立即执行。

问题是，发送消息后，channel 立即断开连接，handler 收不到后面的响应消息。

        ........
    case Sending:
        this.state = State.Disconnecting;
        future.getChannel().disconnect().addListener(this);
        break;
        ........

你根本不应该阻止 channel future 的话题。最好的方法是扩展 SimpleChannelUpstreamHandler 的

    channelConnected(..) {} 
    messageReceived(..) {} 
    channelDisconnected(..) {} 

方法并对这些事件使用react。您也可以将状态保留在该处理程序中。