Exchanger构造在Transporter之上,其重点在于构建数据传输的数据结构,以Transporter作为数据传输手段,实现 Request-Response 信息交换语义

1.HeaderExchanger

HeaderExchangeClient和HeaderExchangeServer是具体实现

public class HeaderExchanger implements Exchanger {

    public static final String NAME = "header";

    @Override
    public ExchangeClient connect(URL url, ExchangeHandler handler) throws RemotingException {
        return new HeaderExchangeClient(Transporters.connect(url, new DecodeHandler(new HeaderExchangeHandler(handler))), true);
    }

    @Override
    public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
        return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
    }

}

2.HeaderExchangeClient

HeaderExchangeClient在具体发送数据时,是由ExchangeChannel实现的,
HeaderExchangeChannel是对Client的封装

public class HeaderExchangeClient implements ExchangeClient {

    private static final Logger logger = LoggerFactory.getLogger(HeaderExchangeClient.class);

    private final Client client;
    private final ExchangeChannel channel;

    public HeaderExchangeClient(Client client, boolean needHeartbeat) {
        if (client == null) {
            throw new IllegalArgumentException("client == null");
        }
        this.client = client;
        this.channel = new HeaderExchangeChannel(client);
    }

    @Override
    public ResponseFuture request(Object request) throws RemotingException {
        return channel.request(request);
    }

    @Override
    public ResponseFuture request(Object request, int timeout) throws RemotingException {
        return channel.request(request, timeout);
    }

    @Override
    public void send(Object message, boolean sent) throws RemotingException {
        channel.send(message, sent);
    }
}

3.HeaderExchangeChannel

可以看到HeaderExchangeChannel内部实际还是调用了Channel相关方法,但其发送的数据封装了Request对象

final class HeaderExchangeChannel implements ExchangeChannel {

    private static final Logger logger = LoggerFactory.getLogger(HeaderExchangeChannel.class);

    private static final String CHANNEL_KEY = HeaderExchangeChannel.class.getName() + ".CHANNEL";

    private final Channel channel;

    private volatile boolean closed = false;

    HeaderExchangeChannel(Channel channel) {
        if (channel == null) {
            throw new IllegalArgumentException("channel == null");
        }
        this.channel = channel;
    }

    static HeaderExchangeChannel getOrAddChannel(Channel ch) {
        if (ch == null) {
            return null;
        }
        HeaderExchangeChannel ret = (HeaderExchangeChannel) ch.getAttribute(CHANNEL_KEY);
        if (ret == null) {
            ret = new HeaderExchangeChannel(ch);
            if (ch.isConnected()) {
                ch.setAttribute(CHANNEL_KEY, ret);
            }
        }
        return ret;
    }

    @Override
    public void send(Object message, boolean sent) throws RemotingException {
        if (closed) {
            throw new RemotingException(this.getLocalAddress(), null, "Failed to send message " + message + ", cause: The channel " + this + " is closed!");
        }
        if (message instanceof Request
                || message instanceof Response
                || message instanceof String) {
            channel.send(message, sent);
        } else {
            Request request = new Request();
            request.setVersion("2.0.0");
            request.setTwoWay(false);
            request.setData(message);
            channel.send(request, sent);
        }
    }

4.心跳检查

HeaderExchangeServer和HeaderExchangeClient同时还实现了Server端和Client的心跳检查

参考:https://www.jianshu.com/p/1e0c8c08e89d