java - 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);
        }
    }

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

Exception in thread "main" java.lang.IllegalArgumentException at org.eclipse.paho.client.mqttv3.MqttClient.(MqttClient.java:170) at mqtt_pub.Thermometer.(Thermometer.java:26) at mqtt_pub.Thermometer.main(Thermometer.java:65)

我发现如果 QoS 的值不是 0、1 或 2，但在 MemoryPersistence 类中他们没有提到，@throws IllegalArgumentException。请帮忙，提前谢谢你。

Answer 1

如果您查看 source code MttqClient 你可以看到 uuid 的长度最多只能是 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()返回一个长度为36个字符的字符串；