Paho MQTT抛出异常

Question

为了演示Paho MQTT，我下载了一个Java示例。

 public class Thermometer {

    public static final String BROKER_URL = "tcp://test.mosquitto.org:1883";

    public static final String TOPIC = "xyz.abc";

    private MqttClient client;


    public Thermometer() {
        try {
            MemoryPersistence per = new MemoryPersistence();
            String clientId = UUID.randomUUID().toString();
            client = new MqttClient(BROKER_URL, clientId, per);
        } catch (MqttException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

当我运行它时，会出现问题，它位于client = new MqttClient(BROKER_URL, clientId, per);

org.eclipse.paho.client.mqttv3.MqttClient.(MqttClient.java:170) at mqtt_pub.Thermometer.(Thermometer.java:26) at mqtt_pub.Thermometer.main(Thermometer.java:65)的线程"main“java.lang.IllegalArgumentException中的异常

我发现，如果IllegalArgumentException的值不是0、1或2，而是在类MemoryPersistence中没有提到，那么@会抛出MemoryPersistence。请帮忙，谢谢。

Answer 1

如果您查看源代码 of MttqClient，您可以看到uuid只能有最大23个字符。看起来uuid更长：

if (clientId == null || clientId.length() == 0 || clientId.length() > 23)  
{
      throw new IllegalArgumentException();
}

UUID.randomUUID().toString()返回长度为36个字符的字符串；