Question

我有一个Java MQTT订阅客户端，它使用订阅的消息作为输入来更新SQLite数据库中的2个表。表格，数据和查询都是轻量级且简单的UPDATE和INSERT操作。这就是我所看到的：

订阅主题收到的消息。
messageArrived回调启动数据库操作。
数据库已成功更新。
控制权来自connectionLost回调。
客户端（即Java进程）终止。

当用System.out.println替换数据库操作时，行为是正常的。我试图摆弄连接选项中的keepAlive值，认为数据库操作可能会影响PINGREQ和PINGRESP（即使客户端处于'后台'）。< / p>

你能否建议，为什么客户失去联系？

Java MQTT客户端：

public class wSync implements MqttCallback {
    MqttClient w;

    private String BROKER_URL = "";
    private String PROTOCOL = "tcp://";
    private String PORT = "1883";
    private String TOPIC_ROOT_UNCNF = "/P/uncnf/";
    private String TOPIC_ROOT_CNF = "/P/cnf/";
    private int KEEP_ALIVE = 180;

    private we WE = new WE();

    public static void main(String[] args) {
        wSync wsy = new wSync();
        processTxns(args[0]);
    }

    public void setBrokerUrl() {
        this.BROKER_URL = PROTOCOL + System.getenv("BROKER_DNS") + ":" + PORT;
    }

    public String getBrokerUrl() {
        return this.BROKER_URL;
    }

    public void processTxns(String wName) {
        this.setBrokerUrl();

        String broker = this.getBrokerUrl();
        String clientId = wName + "-SUB";
        String topic = TOPIC_ROOT_CNF + wName + "/CR";
        MemoryPersistence persistence = new MemoryPersistence();   

        try {
            MqttConnectOptions c = new MqttConnectOptions();
            c.setKeepAliveInterval(KEEP_ALIVE);
            c.setCleanSession(false);

            w = new MqttClient(broker, clientId, persistence);
            w.connect(c);
            w.setCallback(this);
            w.subscribe(topic, 2);
            System.out.println(w.getServerURI() + " " + w.getClientId() + " " + w.isConnected());

        } catch (MqttException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void connectionLost(Throwable arg0) {
        System.out.println("Connection lost at : " + new SimpleDateFormat("yyyy-MM-dd.HH:mm:ss").format(new java.util.Date()));
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void messageArrived(String topic, MqttMessage message) throws Exception {
        String s = new String(message.getPayload());
        we.addSeed(s);
    }
}

更新

由于我不确定，为什么断线发生，我决定处理它。毕竟，现场部署中的网络错误并非闻所未闻。所以，我重新写了connectionLost回调：

@Override
public void connectionLost(Throwable arg0) {
    System.out.println("A " + w.isConnected() + " " + new SimpleDateFormat("yyyy-MM-dd.HH:mm:ss").format(new java.util.Date()));

    try {
        w.connect(mqttConn);
        w.setCallback(this);
        w.subscribe("/P/cnf/wA/CR", 2);
    } catch (MqttSecurityException e) {
        e.printStackTrace();
    } catch (MqttException e) {
        e.printStackTrace();
    }

    System.out.println("B " + w.isConnected() + " " + new SimpleDateFormat("yyyy-MM-dd.HH:mm:ss").format(new java.util.Date()));
}

这似乎可以处理在主题上发布的消息的断开和接收。但是，如果留给自己（意味着没有收到出版物），我会看到以下错误消息：

champ@champ:~/bin$ java -jar w-sync.jar pull wA
* true 2017-02-19.23:21:00
{
  "meta" : {"tStamp" : "current_Date"},
  "data" : 
    [
      {"txn" : "thingy,thingamajig,whatchamacallit"}
    ]
}

A false 2017-02-19.23:21:29
B true 2017-02-19.23:21:29
A false 2017-02-19.23:22:29
A false 2017-02-19.23:22:29
B true 2017-02-19.23:22:29
MqttException (0) - java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:171)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at java.util.Vector.removeElementAt(Vector.java:558)
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:137)
    ... 1 more
B true 2017-02-19.23:22:29
A false 2017-02-19.23:24:29
MqttException (0) - java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:171)
    at java.lang.Thread.run(Thread.java:745)
A false 2017-02-19.23:24:29
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at java.util.Vector.removeElementAt(Vector.java:558)
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:137)
    ... 1 more
B false 2017-02-19.23:24:29
MqttException (0) - java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:171)
    at java.lang.Thread.run(Thread.java:745)
A false 2017-02-19.23:24:29
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
    at java.util.Vector.removeElementAt(Vector.java:558)
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:137)
    ... 1 more
B false 2017-02-19.23:24:29
Client is not connected (32104)
    at org.eclipse.paho.client.mqttv3.internal.ExceptionHelper.createMqttException(ExceptionHelper.java:27)
    at org.eclipse.paho.client.mqttv3.internal.ClientComms.sendNoWait(ClientComms.java:132)
    at org.eclipse.paho.client.mqttv3.MqttAsyncClient.subscribe(MqttAsyncClient.java:657)
    at org.eclipse.paho.client.mqttv3.MqttClient.subscribe(MqttClient.java:282)
    at org.eclipse.paho.client.mqttv3.MqttClient.subscribe(MqttClient.java:275)A false 2017-02-19.23:24:29

    at com.rpk.demo.sync.wSync.connectionLost(wSync.java:109)
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.connectionLost(CommsCallback.java:229)
    at org.eclipse.paho.client.mqttv3.internal.ClientComms.shutdownConnection(ClientComms.java:339)
    at org.eclipse.paho.client.mqttv3.internal.CommsCallback.run(CommsCallback.java:171)
    at java.lang.Thread.run(Thread.java:745)
B false 2017-02-19.23:24:29
B true 2017-02-19.23:24:29

数据库操作后，MQTT订阅客户端断开连接

0 个答案: