Question

我是IoTHub的新手。我已经使用python成功地向IOT中心（D2C）发送了消息。我们使用的协议是mqtt。我们正在尝试使用java从云（IOT中心）检索数据，但无法找到从中接收消息的正确方法我怀疑的是我们是否可以直接从IOT Hub读取消息，或者我们需要将传入的消息重定向到事件中心以检索消息。

此外，我尝试在将数据发送到云时同时从java中读取来自iothub的消息，但是我得到了如下错误..（丢失了与服务器的连接。重新连接0次。）

我使用此代码从iothub读取数据，

import com.microsoft.azure.sdk.iot.device.DeviceClient;
import com.microsoft.azure.sdk.iot.device.IotHubMessageResult;
import com.microsoft.azure.sdk.iot.device.Message;
import com.microsoft.azure.sdk.iot.device.MessageCallback;
import com.microsoft.azure.sdk.iot.device.IotHubClientProtocol;
import com.microsoft.azure.sdk.iot.service.sdk.IotHubServiceClientProtocol;
import java.io.IOException;
import java.net.URISyntaxException;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Kafkareception {

    public static void main(String[] args) throws IOException {
        try {
            String connString = "HostName=";
            IotHubClientProtocol protocol = IotHubClientProtocol.MQTT;
            DeviceClient client = new DeviceClient(connString, protocol);

            MessageCallback callback = new AppMessageCallback();
            client.setMessageCallback(callback, null);
            client.open();
        } catch (URISyntaxException ex) {
            Logger.getLogger(Kafkareception.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    private static class AppMessageCallback implements MessageCallback {

        public IotHubMessageResult execute(Message msg, Object context) {
            System.out.println(new String(msg.getBytes(), Message.DEFAULT_IOTHUB_MESSAGE_CHARSET) + "Received message from hub: ");

            return IotHubMessageResult.COMPLETE;
        }
    }
}

Answer 1

根据您提供的信息，您可能尝试使用DeviceClient将一个设备的两个活动连接设置到Azure IoT Hub：一个发送D2C消息，一个是“从iothub读取数据 ”。你得到错误可能是因为：

IoT Hub仅支持每个设备一个活动的MQTT连接。任何新的代表相同设备ID的MQTT连接会导致IoT Hub丢弃现有的连接。

参考：Communicate with your IoT hub using the MQTT protocol

如果要接收发送到Azure IoT Hub的D2C消息，可以use Event Hub-compatible endpoint(Java)。无需自己将传入的消息重定向到事件中心。

IoT Hub为您的内容公开消息/事件内置端点后端服务，用于读取接收到的设备到云消息你的中心。此端点与Event Hub兼容，使您可以使用Event Hubs服务支持的任何机制进行阅读消息。

参考：Understand Azure IoT Hub messaging和IoT Hub endpoints。

Answer 2

我从iothub读取数据。我们可以使用代码

import java.io.IOException;
import com.microsoft.azure.eventhubs.*;
import com.microsoft.azure.servicebus.*;

import java.nio.charset.Charset;
import java.time.*;
import java.util.function.*;

public class Datafetch {

    public static void main(String[] args) throws IOException {
        EventHubClient client0 = receiveMessages("0");
        EventHubClient client1 = receiveMessages("1");
        System.out.println("Press ENTER to exit.");
        System.in.read();
        try {
            client0.closeSync();
            client1.closeSync();
            System.exit(0);
        } catch (ServiceBusException sbe) {
            System.exit(1);
        }
    }

private static EventHubClient receiveMessages(final String partitionId) {

        String connStr = "Endpoint={youreventhubcompatibleendpoint};EntityPath={youreventhubcompatiblename};SharedAccessKeyName=iothubowner;SharedAccessKey={youriothubkey}";
        EventHubClient client = null;
        try {
            client = EventHubClient.createFromConnectionStringSync(connStr);
        } catch (Exception e) {
            System.out.println("Failed to create client: " + e.getMessage());
            System.exit(1);
        }
        try {
            client.createReceiver(
                    EventHubClient.DEFAULT_CONSUMER_GROUP_NAME,
                    partitionId,
                    Instant.now()).thenAccept(new Consumer<PartitionReceiver>() {
                        public void accept(PartitionReceiver receiver) {
                            System.out.println("** Created receiver on partition " + partitionId);
                            try {
                                while (true) {
                                    Iterable<EventData> receivedEvents = receiver.receive(100).get();
                                    System.out.println(receivedEvents);
                                    int batchSize = 0;
                                    if (receivedEvents != null) {
                                        for (EventData receivedEvent : receivedEvents) {
                                            System.out.println(String.format("Offset: %s, SeqNo: %s, EnqueueTime: %s",
                                                    receivedEvent.getSystemProperties().getOffset(),
                                                    receivedEvent.getSystemProperties().getSequenceNumber(),
                                                    receivedEvent.getSystemProperties().getEnqueuedTime()));
                                            System.out.println(String.format("| Device ID: %s", receivedEvent.getSystemProperties().getClass()));
                                            System.out.println(String.format("| Message Payload: %s", new String(receivedEvent.getBody(),
                                                    Charset.defaultCharset())));
                                            batchSize++;
                                        }
                                    }
                                    System.out.println(String.format("Partition: %s, ReceivedBatch Size: %s", partitionId, batchSize));
                                }
                            } catch (Exception e) {
                                System.out.println("Failed to receive messages: " + e.getMessage());
                            }
                        }
                    });
        } catch (Exception e) {
            System.out.println("Failed to create receiver: " + e.getMessage());
        }
        return client;
    }
}

如何使用java中的mqtt从云（iothub）中检索数据

2 个答案: