使用Netty的異步HTTP客戶端

Question

我是netty的新手，仍然喜歡找我的路。 我正在尋找創建一個異步工作的http客戶端。 http的netty示例僅顯示如何等待IO操作，而不是如何使用addListener ，因此我一直試圖在過去幾天解決這個問題。

我正在嘗試創建一個請求類，它將處理請求的所有不同狀態，包括連接，發送數據，處理響應，然后關閉連接。 為了做到這一點，我的類擴展了SimpleChannelUpstreamHandler並實現了ChannelFutureListener 。 我使用ChannelPipelineFactory將類（作為SimpleChannelUpstreamHandler ）的（this）實例作為處理程序添加到管道。

連接創建如下：

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;
}

該類還會覆蓋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));
    }
}

問題是我得到了這個輸出：

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

正如您所看到的，由於某種原因，即使管道工廠將此類的實例添加到管道中，因此仍未執行messageReceived 。

我在這里缺少什么想法？ 謝謝。

---

編輯

在@JestanNirojan的幫助下，我終於得到了這個工作，以防有人對該解決方案感興趣：

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來執行通道中的所有操作（這是錯誤的），並且將在調用這些通道操作后立即執行將來的偵聽器。

問題是，在發送消息后，通道立即斷開，處理程序無法接收稍后出現的響應消息。

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

你不應該阻止頻道未來的線程。 最好的方法是擴展SimpleChannelUpstreamHandler

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

方法並對這些事件做出反應。 你也可以把狀態保持在那個處理程序中。