Apache Camel PAHO MQTT 组件断开连接后收不到消息答案

【问题标题】：Apache Camel PAHO MQTT component does not receive messages after disconnectingApache Camel PAHO MQTT 组件断开连接后收不到消息
【发布时间】：2020-09-21 23:18:52
【问题描述】：

我在这里看到了同样的问题，但不明白如何根据响应解决此问题。

Camel PAHO routes not receiving offline messages while connecting back

是否可以在 paho 端点接收离线消息，如果可以，如何？这需要修改源代码吗？

我确认我在命令行中使用 mosquitto_sub 收到了离线消息。

这是我的端点配置：

<from uri="paho:JUNK?brokerUrl=tcp://localhost:1883?cleanSession=false&amp;qos=2&amp;clientId=camel_test" />

更多细节。似乎在断开骆驼客户端时，客户端首先取消订阅，这导致客户端在重新连接时无法接收离线消息。

Sep 21 06:33:40 me mosquitto.mosquitto[1290]: 1600684420: camel_test JUNK
Sep 21 06:33:40 me mosquitto.mosquitto[1290]: 1600684420: Sending UNSUBACK to camel_test
Sep 21 06:33:40 me mosquitto.mosquitto[1290]: 1600684420: Received DISCONNECT from camel_test
Sep 21 06:33:40 me mosquitto.mosquitto[1290]: 1600684420: Client camel_test disconnected.

mosquitto_sub 命令行客户端不会在断开连接时取消订阅，因此能够在重新连接时接收离线消息。

Sep 21 06:33:21 me mosquitto.mosquitto[1290]: 1600684400: Client ns_consumer disconnected.
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: New client connected from ::1 as ns_consumer (p2, c0, k60).
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending CONNACK to ns_consumer (1, 0)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending PUBLISH to ns_consumer (d0, q2, r0, m26, 'JUNK', ... (189 bytes))
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Received SUBSCRIBE from ns_consumer
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: ns_consumer 2 JUNK
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending SUBACK to ns_consumer
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending PUBLISH to ns_consumer (d0, q2, r1, m27, 'JUNK', ... (189 bytes))
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Received PUBREC from ns_consumer (Mid: 26)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending PUBREL to ns_consumer (m26)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Received PUBREC from ns_consumer (Mid: 27)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Sending PUBREL to ns_consumer (m27)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Received PUBCOMP from ns_consumer (Mid: 26, RC:0)
Sep 21 06:42:23 me mosquitto.mosquitto[1290]: 1600684943: Received PUBCOMP from ns_consumer (Mid: 27, RC:0)

【问题讨论】：

你用的是什么版本的骆驼？
我使用的是 3.4.3 版。想知道这是否可能是由于客户端在断开连接时首先取消订阅？是否有解决此问题的更新版本？
已验证在骆驼 3.5.0 中出现相同的取消订阅功能
没关系...找出问题所在。 url 语法不正确，因此从未设置 cleanSession。

标签： apache-camel mqtt paho spring-camel

【解决方案1】：

问题是端点配置中的语法不正确，因此 cleanSession 从未通过参数设置并默认为 true。

<from uri="paho:JUNK?brokerUrl=tcp://localhost:1883?cleanSession=false&amp;qos=2&amp;clientId=camel_test" />

应该是

<from uri="paho:JUNK?brokerUrl=tcp://localhost:1883&amp;cleanSession=false&amp;qos=2&amp;clientId=camel_test" />

【讨论】：