物联网协议之MQTT源码分析(二)
此篇文章继上一篇物联网协议之MQTT源码分析(一)而写的第二篇MQTT发布消息以及接收Broker消息的源码分析，想看MQTT链接的小伙伴能够去看我上一篇哦。bash
MQTT发布消息
MQTT发布消息是由MqttAndroidClient类的publish函数执行的，咱们来看看这个函数：socket
// MqttAndroidClient类：
@Override
public IMqttDeliveryToken publish(String topic, byte[] payload, int qos,
boolean retained, Object userContext,
IMqttActionListener callback)
throws MqttException, MqttPersistenceException {
// 将消息内容、qos消息等级、retained消息是否保留封装成MqttMessage
MqttMessage message = new MqttMessage(payload);
message.setQos(qos);
message.setRetained(retained);
// 每一条消息都有本身的token
MqttDeliveryTokenAndroid token = new MqttDeliveryTokenAndroid(
this, userContext, callback, message);
String activityToken = storeToken(token);
IMqttDeliveryToken internalToken = mqttService.publish(clientHandle,
topic, payload, qos, retained, null, activityToken);
token.setDelegate(internalToken);
return token;
}
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从上面代码能够看出，发布消息须要topic消息主题、payload消息内容、callback回调监听等，经由mqttService.publish继续执行发布操做：async
// MqttService类：MQTT惟一组件
public IMqttDeliveryToken publish(String clientHandle, String topic,
byte[] payload, int qos, boolean retained,
String invocationContext, String activityToken)
throws MqttPersistenceException, MqttException {
MqttConnection client = getConnection(clientHandle);
return client.publish(topic, payload, qos, retained, invocationContext,
activityToken);
}
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MqttConnection在上一篇中讲解过，MQTT的链接会初始化一个MqttConnection，并保存在一个Map集合connections中，并经过getConnection(clientHandle)方法获取。很明显咱们要接着看client.publish函数啦：ide
// MqttConnection类：
public IMqttDeliveryToken publish(String topic, byte[] payload, int qos,
boolean retained, String invocationContext,
String activityToken) {
// 用于发布消息，是否发布成功的回调
final Bundle resultBundle = new Bundle();
resultBundle.putString(MqttServiceConstants.CALLBACK_ACTION,
MqttServiceConstants.SEND_ACTION);
resultBundle.putString(MqttServiceConstants.CALLBACK_ACTIVITY_TOKEN,
activityToken);
resultBundle.putString(
MqttServiceConstants.CALLBACK_INVOCATION_CONTEXT,
invocationContext);
IMqttDeliveryToken sendToken = null;
if ((myClient != null) && (myClient.isConnected())) {
// 携带resultBundle数据，用于监听回调发布消息是否成功
IMqttActionListener listener = new MqttConnectionListener(
resultBundle);
try {
MqttMessage message = new MqttMessage(payload);
message.setQos(qos);
message.setRetained(retained);
sendToken = myClient.publish(topic, payload, qos, retained,
invocationContext, listener);
storeSendDetails(topic, message, sendToken, invocationContext,
activityToken);
} catch (Exception e) {
handleException(resultBundle, e);
}
} else {
resultBundle.putString(MqttServiceConstants.CALLBACK_ERROR_MESSAGE,
NOT_CONNECTED);
service.traceError(MqttServiceConstants.SEND_ACTION, NOT_CONNECTED);
service.callbackToActivity(clientHandle, Status.ERROR, resultBundle);
}
return sendToken;
}
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这段代码中很明显能够看出发布的操做又交给了myClient.publish方法，那myClient是谁呢？上一篇文章中讲过myClient是MqttAsyncClient，是在MQTT链接时在MqttConnection类的connect方法中初始化的，详情请看上一篇。函数
// MqttAsyncClient类：
public IMqttDeliveryToken publish(String topic, byte[] payload, int qos
, boolean retained,Object userContext,
IMqttActionListener callback) throws MqttException,MqttPersistenceException {
MqttMessage message = new MqttMessage(payload);
message.setQos(qos);
message.setRetained(retained);
return this.publish(topic, message, userContext, callback);
}
public IMqttDeliveryToken publish(String topic, MqttMessage message
, Object userContext,
IMqttActionListener callback) throws MqttException,MqttPersistenceException {
final String methodName = "publish";
// @TRACE 111=< topic={0} message={1}userContext={1} callback={2}
log.fine(CLASS_NAME, methodName, "111", new Object[]{topic, userContext, callback});
// Checks if a topic is valid when publishing a message.
MqttTopic.validate(topic, false/* wildcards NOT allowed */);
MqttDeliveryToken token = new MqttDeliveryToken(getClientId());
token.setActionCallback(callback);
token.setUserContext(userContext);
token.setMessage(message);
token.internalTok.setTopics(new String[]{topic});
MqttPublish pubMsg = new MqttPublish(topic, message);
comms.sendNoWait(pubMsg, token);
// @TRACE 112=<
log.fine(CLASS_NAME, methodName, "112");
return token;
}
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从这段代码中能够看到，如今把把topic和message封装成了MqttPublish类型的消息，并继续由comms.sendNoWait执行，comms是ClientComms，ClientComms是在初始化MqttAsyncClient的构造方法中初始化的，详情看上一篇。源码分析
// ClientComms类：
public void sendNoWait(MqttWireMessage message, MqttToken token) throws MqttException {
final String methodName = "sendNoWait";
// 判断状态或者消息类型
if (isConnected() ||
(!isConnected() && message instanceof MqttConnect) ||
(isDisconnecting() && message instanceof MqttDisconnect)) {
if (disconnectedMessageBuffer != null && disconnectedMessageBuffer.getMessageCount() != 0) {
//@TRACE 507=Client Connected, Offline Buffer available, but not empty. Adding
// message to buffer. message={0}
log.fine(CLASS_NAME, methodName, "507", new Object[]{message.getKey()});
if (disconnectedMessageBuffer.isPersistBuffer()) {
this.clientState.persistBufferedMessage(message);
}
disconnectedMessageBuffer.putMessage(message, token);
} else {
// 如今不是disconnect所以，逻辑走这里
this.internalSend(message, token);
}
} else if (disconnectedMessageBuffer != null) {
//@TRACE 508=Offline Buffer available. Adding message to buffer. message={0}
log.fine(CLASS_NAME, methodName, "508", new Object[]{message.getKey()});
if (disconnectedMessageBuffer.isPersistBuffer()) {
this.clientState.persistBufferedMessage(message);
}
disconnectedMessageBuffer.putMessage(message, token);
} else {
//@TRACE 208=failed: not connected
log.fine(CLASS_NAME, methodName, "208");
throw ExceptionHelper.createMqttException(MqttException.REASON_CODE_CLIENT_NOT_CONNECTED);
}
}
void internalSend(MqttWireMessage message, MqttToken token) throws MqttException {
final String methodName = "internalSend";
...
try {
// Persist if needed and send the message
this.clientState.send(message, token);
} catch (MqttException e) {
// 注意此处代码***
if (message instanceof MqttPublish) {
this.clientState.undo((MqttPublish) message);
}
throw e;
}
}
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comms.sendNoWait方法中又调用了本类中的internalSend方法，而且在internalSend方法中又调用了clientState.send(message, token)方法继续发布。ClientState对象是在ClientComms初始化的构造方法中初始化的。此处须要注意一下catch里的代码，下面会具体说明。post
// ClientState类：
public void send(MqttWireMessage message, MqttToken token) throws MqttException {
final String methodName = "send";
...
if (message instanceof MqttPublish) {
synchronized (queueLock) {
/**
* 注意这里：actualInFlight实际飞行中>maxInflight最大飞行中
* maxInflight：是咱们在本身代码中经过链接选项MqttConnectOptions.setMaxInflight();设置的，默认大小为10
*/
if (actualInFlight >= this.maxInflight) {
//@TRACE 613= sending {0} msgs at max inflight window
log.fine(CLASS_NAME, methodName, "613",
new Object[]{new Integer(actualInFlight)});
throw new MqttException(MqttException.REASON_CODE_MAX_INFLIGHT);
}
MqttMessage innerMessage = ((MqttPublish) message).getMessage();
//@TRACE 628=pending publish key={0} qos={1} message={2}
log.fine(CLASS_NAME, methodName, "628",
new Object[]{new Integer(message.getMessageId()),
new Integer(innerMessage.getQos()), message});
/**
* 根据本身设置的qos等级，来决定是否须要恢复消息
* 这里须要说明一下qos等级区别：
* qos==0，至多发送一次，不进行重试，Broker不会返回确认消息。
* qos==1，至少发送一次，确保消息到达Broker，Broker须要返回确认消息PUBACK
* qos==2，Broker确定会收到消息，且只收到一次，qos==1可能会发送重复消息
*/
switch (innerMessage.getQos()) {
case 2:
outboundQoS2.put(new Integer(message.getMessageId()), message);
persistence.put(getSendPersistenceKey(message), (MqttPublish) message);
break;
case 1:
outboundQoS1.put(new Integer(message.getMessageId()), message);
persistence.put(getSendPersistenceKey(message), (MqttPublish) message);
break;
}
tokenStore.saveToken(token, message);
pendingMessages.addElement(message);
queueLock.notifyAll();
}
} else {
...
}
}
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这段代码中咱们发现了一个可能须要咱们本身设置的属性maxInflight，若是实际发送中的消息大于maxInflight约束的最大的话就会抛出MqttException异常，那么这个异常catch里是怎么处理的呢，这就要往回看一步代码啦，上面已经提示过须要注意ClientComms类中internalSend方法中的catch里的代码：ui
if (message instanceof MqttPublish) {
this.clientState.undo((MqttPublish) message);
}
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能够很明确的看出若消息类型是MqttPublish，则执行clientState.undo((MqttPublish) message)方法，咱们前面说过消息已经在MqttAsyncClient类的publish方法中把topic和message封装成了MqttPublish类型的消息，所以此处会执行undo方法：this
// ClientState类：
protected void undo(MqttPublish message) throws MqttPersistenceException {
final String methodName = "undo";
synchronized (queueLock) {
//@TRACE 618=key={0} QoS={1}
log.fine(CLASS_NAME, methodName, "618",
new Object[]{new Integer(message.getMessageId()),
new Integer(message.getMessage().getQos())});
if (message.getMessage().getQos() == 1) {
outboundQoS1.remove(new Integer(message.getMessageId()));
} else {
outboundQoS2.remove(new Integer(message.getMessageId()));
}
pendingMessages.removeElement(message);
persistence.remove(getSendPersistenceKey(message));
tokenStore.removeToken(message);
if (message.getMessage().getQos() > 0) {
//Free this message Id so it can be used again
releaseMessageId(message.getMessageId());
message.setMessageId(0);
}
checkQuiesceLock();
}
}
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代码已经很明显了，就是把大于maxInflight这部分消息remove移除掉，所以在实际操做中要注意本身的Mqtt消息的发布会不会在短期内达到maxInflight默认的10的峰值，若能达到，则须要手动设置一个适合本身项目的范围阀值啦。
咱们继续说clientState.send(message, token)方法里的逻辑，代码中注释中也说明了Mqtt会根据qos等级来决定消息到达机制
qos等级
- qos==0，至多发送一次，不进行重试，Broker不会返回确认消息，消息可能会丢失。
- qos==1，至少发送一次，确保消息到达Broker，Broker须要返回确认消息PUBACK，可能会发送重复消息
- qos==2，Broker确定会收到消息，且只收到一次
根据qos等级，若qos等于1和2，则讲消息分别加入Hashtable类型的outboundQoS1和outboundQoS2中，已在后续逻辑中确保消息发送成功并到达。
注：qos等级优先级没有maxInflight高，从代码中能够看出，会先判断maxInflight再区分qos等级
代码的最后讲消息添加进Vector类型的pendingMessages里，在上一篇中咱们能够了解到MQTT的发射器是轮询检查pendingMessages里是否存在数据，若存在则经过socket的OutputStream发送出去。而且会经过接收器接收从Broker发送回来的数据。
监听Broker返回的消息之数据
发送咱们就不看源码啦，接收咱们再看一下源码，经过源码看一看数据是怎么回到咱们本身的回调里的：
// CommsReceiver类中：
public void run() {
recThread = Thread.currentThread();
recThread.setName(threadName);
final String methodName = "run";
MqttToken token = null;
try {
runningSemaphore.acquire();
} catch (InterruptedException e) {
running = false;
return;
}
while (running && (in != null)) {
try {
//@TRACE 852=network read message
log.fine(CLASS_NAME, methodName, "852");
receiving = in.available() > 0;
MqttWireMessage message = in.readMqttWireMessage();
receiving = false;
// 消息是否属于Mqtt确认类型
if (message instanceof MqttAck) {
token = tokenStore.getToken(message);
// token通常不会为空，前面已经保存过
if (token != null) {
synchronized (token) {
// ...
clientState.notifyReceivedAck((MqttAck) message);
}
}
...
} finally {
receiving = false;
runningSemaphore.release();
}
}
}
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从代码中能够看出，Broker返回来的数据交给了clientState.notifyReceivedAck方法：
// ClientState类：
protected void notifyReceivedAck(MqttAck ack) throws MqttException {
final String methodName = "notifyReceivedAck";
...
MqttToken token = tokenStore.getToken(ack);
MqttException mex = null;
if (token == null) {
...
} else if (ack instanceof MqttPubRec) {
// qos==2 是返回
MqttPubRel rel = new MqttPubRel((MqttPubRec) ack);
this.send(rel, token);
} else if (ack instanceof MqttPubAck || ack instanceof MqttPubComp) {
// qos==1/2 消息移除前通知的结果
notifyResult(ack, token, mex);
// Do not remove publish / delivery token at this stage
// do this when the persistence is removed later
} else if (ack instanceof MqttPingResp) {
// 链接心跳数据消息
...
} else if (ack instanceof MqttConnack) {
// MQTT链接消息
...
} else {
notifyResult(ack, token, mex);
releaseMessageId(ack.getMessageId());
tokenStore.removeToken(ack);
}
checkQuiesceLock();
}
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从上面注释可知，发布的消息qos==0，返回结果是直接走else，而qos==1/2，确认消息也最终会走到notifyResult(ack, token, mex)方法中：
protected void notifyResult(MqttWireMessage ack, MqttToken token, MqttException ex) {
final String methodName = "notifyResult";
// 取消阻止等待令牌的任何线程，并保存ack
token.internalTok.markComplete(ack, ex);
// 通知此令牌已收到响应消息，设置已完成状态，并经过isComplete()获取状态
token.internalTok.notifyComplete();
// 让用户知道异步操做已完成，而后删除令牌
if (ack != null && ack instanceof MqttAck && !(ack instanceof MqttPubRec)) {
//@TRACE 648=key{0}, msg={1}, excep={2}
log.fine(CLASS_NAME, methodName, "648", new Object[]{token.internalTok.getKey(), ack,ex});
// CommsCallback类
callback.asyncOperationComplete(token);
}
// 有些状况下，因为操做失败，所以没有确认
if (ack == null) {
//@TRACE 649=key={0},excep={1}
log.fine(CLASS_NAME, methodName, "649", new Object[]{token.internalTok.getKey(), ex});
callback.asyncOperationComplete(token);
}
}
// Token类：
protected void markComplete(MqttWireMessage msg, MqttException ex) {
final String methodName = "markComplete";
//@TRACE 404=>key={0} response={1} excep={2}
log.fine(CLASS_NAME, methodName, "404", new Object[]{getKey(), msg, ex});
synchronized (responseLock) {
// ACK means that everything was OK, so mark the message for garbage collection.
if (msg instanceof MqttAck) {
this.message = null;
}
this.pendingComplete = true;
// 将消息保存在response成员变量中，并经过getWireMessage()方法获取消息msg
this.response = msg;
this.exception = ex;
}
}
// Token类：
protected void notifyComplete() {
...
synchronized (responseLock) {
...
if (exception == null && pendingComplete) {
// 设置已完成，并经过isComplete()获取状态
completed = true;
pendingComplete = false;
} else {
pendingComplete = false;
}
responseLock.notifyAll();
}
...
}
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此时已将MqttWireMessage消息保存到token中，异步操做已完成，调用回调监听CommsCallback里的asyncOperationComplete方法：
// CommsCallback类：
public void asyncOperationComplete(MqttToken token) {
final String methodName = "asyncOperationComplete";
if (running) {
// invoke callbacks on callback thread
completeQueue.addElement(token);
synchronized (workAvailable) {
// @TRACE 715=new workAvailable. key={0}
log.fine(CLASS_NAME, methodName, "715", new Object[]{token.internalTok.getKey()});
workAvailable.notifyAll();
}
} else {
// invoke async callback on invokers thread
try {
handleActionComplete(token);
} catch (Throwable ex) {
// Users code could throw an Error or Exception e.g. in the case
// of class NoClassDefFoundError
// @TRACE 719=callback threw ex:
log.fine(CLASS_NAME, methodName, "719", null, ex);
// Shutdown likely already in progress but no harm to confirm
clientComms.shutdownConnection(null, new MqttException(ex));
}
}
}
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CommsCallback是Mqtt链接就已经开始一直运行，所以running为true，因此如今已经将token添加进了completeQueue完成队列中，CommsCallback跟发射器同样，一直轮询等待数据，所以此时completeQueue已有数据，此时CommsCallback的run函数则会有接下来的操做：
// CommsCallback类：
public void run() {
...
while (running) {
try {
...
if (running) {
// Check for deliveryComplete callbacks...
MqttToken token = null;
synchronized (completeQueue) {
// completeQueue不为空
if (!completeQueue.isEmpty()) {
// 获取第一个token
token = (MqttToken) completeQueue.elementAt(0);
completeQueue.removeElementAt(0);
}
}
if (null != token) {
// token不为null，执行handleActionComplete
handleActionComplete(token);
}
...
}
if (quiescing) {
clientState.checkQuiesceLock();
}
} catch (Throwable ex) {
...
} finally {
...
}
}
}
private void handleActionComplete(MqttToken token)
throws MqttException {
final String methodName = "handleActionComplete";
synchronized (token) {
// 由上面已经，isComplete()已设置为true
if (token.isComplete()) {
// Finish by doing any post processing such as delete
// from persistent store but only do so if the action
// is complete
clientState.notifyComplete(token);
}
// 取消阻止任何服务员，若是待完成，如今设置完成
token.internalTok.notifyComplete();
if (!token.internalTok.isNotified()) {
...
// 如今调用异步操做完成回调
fireActionEvent(token);
}
...
}
}
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run中调用了handleActionComplete函数，接着后调用了clientState.notifyComplete()方法和fireActionEvent(token)方法，先看notifyComplete()：
// ClientState类：
protected void notifyComplete(MqttToken token) throws MqttException {
final String methodName = "notifyComplete";
// 获取保存到Token中的Broker返回的消息，上面有说明
MqttWireMessage message = token.internalTok.getWireMessage();
if (message != null && message instanceof MqttAck) {
...
MqttAck ack = (MqttAck) message;
if (ack instanceof MqttPubAck) {
// qos==1,用户通知如今从持久性中删除
persistence.remove(getSendPersistenceKey(message));
persistence.remove(getSendBufferedPersistenceKey(message));
outboundQoS1.remove(new Integer(ack.getMessageId()));
decrementInFlight();
releaseMessageId(message.getMessageId());
tokenStore.removeToken(message);
// @TRACE 650=removed Qos 1 publish. key={0}
log.fine(CLASS_NAME, methodName, "650",
new Object[]{new Integer(ack.getMessageId())});
} else if (ack instanceof MqttPubComp) {
...
}
checkQuiesceLock();
}
}
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再来看fireActionEvent(token)方法：
// CommsCallback类：
public void fireActionEvent(MqttToken token) {
final String methodName = "fireActionEvent";
if (token != null) {
IMqttActionListener asyncCB = token.getActionCallback();
if (asyncCB != null) {
if (token.getException() == null) {
...
asyncCB.onSuccess(token);
} else {
...
asyncCB.onFailure(token, token.getException());
}
}
}
}
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从这段代码中终于能看到回调onSuccess和onFailure的方法啦，那asyncCB是谁呢？
// MqttToken类：
public IMqttActionListener getActionCallback() {
return internalTok.getActionCallback();
}
// Token类：
public IMqttActionListener getActionCallback() {
return callback;
}
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看到这，一脸懵逼，这究竟是谁呢，其实咱们能够直接看这个回调设置方法，看看是从哪设置进来的就能够啦：
// Token类：
public void setActionCallback(IMqttActionListener listener) {
this.callback = listener;
}
// MqttToken类：
public void setActionCallback(IMqttActionListener listener) {
internalTok.setActionCallback(listener);
}
// ConnectActionListener类：
public void connect() throws MqttPersistenceException {
// 初始化MqttToken
MqttToken token = new MqttToken(client.getClientId());
// 将此类设置成回调类
token.setActionCallback(this);
token.setUserContext(this);
...
}
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其实早在MQTT链接时，就已经将此callback设置好，所以asyncCB就是ConnectActionListener，因此此时就已经走到了ConnectActionListener类里的onSuccess和onFailure的方法中，咱们只挑一个onSuccess看一看：
// ConnectActionListener类：
public void onSuccess(IMqttToken token) {
if (originalMqttVersion == MqttConnectOptions.MQTT_VERSION_DEFAULT) {
options.setMqttVersion(MqttConnectOptions.MQTT_VERSION_DEFAULT);
}
// 此时将Broker的数据保存进了userToken里
userToken.internalTok.markComplete(token.getResponse(), null);
userToken.internalTok.notifyComplete();
userToken.internalTok.setClient(this.client);
comms.notifyConnect();
if (userCallback != null) {
userToken.setUserContext(userContext);
userCallback.onSuccess(userToken);
}
if (mqttCallbackExtended != null) {
String serverURI =
comms.getNetworkModules()[comms.getNetworkModuleIndex()].getServerURI();
mqttCallbackExtended.connectComplete(reconnect, serverURI);
}
}
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这里的userCallback又是谁呢？上一篇其实说过的，userCallback其实就是MqttConnection.connect函数中IMqttActionListener listener，因此此时又来到了MqttConnection类里connect方法里的listener监听回调内：
// MqttConnection类：
public void connect(MqttConnectOptions options, String invocationContext,
String activityToken) {
...
service.traceDebug(TAG, "Connecting {" + serverURI + "} as {" + clientId + "}");
final Bundle resultBundle = new Bundle();
resultBundle.putString(MqttServiceConstants.CALLBACK_ACTIVITY_TOKEN,
activityToken);
resultBundle.putString(
MqttServiceConstants.CALLBACK_INVOCATION_CONTEXT,
invocationContext);
resultBundle.putString(MqttServiceConstants.CALLBACK_ACTION,
MqttServiceConstants.CONNECT_ACTION);
try {
...
// 此时逻辑已经来到这里
IMqttActionListener listener = new MqttConnectionListener(
resultBundle) {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// 执行以下代码：
doAfterConnectSuccess(resultBundle);
service.traceDebug(TAG, "connect success!");
}
@Override
public void onFailure(IMqttToken asyncActionToken,
Throwable exception) {
resultBundle.putString(
MqttServiceConstants.CALLBACK_ERROR_MESSAGE,
exception.getLocalizedMessage());
resultBundle.putSerializable(
MqttServiceConstants.CALLBACK_EXCEPTION, exception);
service.traceError(TAG,
"connect fail, call connect to reconnect.reason:"
+ exception.getMessage());
doAfterConnectFail(resultBundle);
}
};
if (myClient != null) {
if (isConnecting) {
...
} else {
service.traceDebug(TAG, "myClient != null and the client is not connected");
service.traceDebug(TAG, "Do Real connect!");
setConnectingState(true);
myClient.connect(connectOptions, invocationContext, listener);
}
}
// if myClient is null, then create a new connection
else {
...
myClient.connect(connectOptions, invocationContext, listener);
}
} catch (Exception e) {
...
}
}
复制代码
由这段代码以及注释能够知道，如今以及执行到了MqttConnection类里的doAfterConnectSuccess方法里：
// MqttConnection类:
private void doAfterConnectSuccess(final Bundle resultBundle) {
// 获取唤醒锁
acquireWakeLock();
service.callbackToActivity(clientHandle, Status.OK, resultBundle);
deliverBacklog();
setConnectingState(false);
disconnected = false;
// 释放唤醒锁
releaseWakeLock();
}
private void deliverBacklog() {
Iterator<StoredMessage> backlog = service.messageStore
.getAllArrivedMessages(clientHandle);
while (backlog.hasNext()) {
StoredMessage msgArrived = backlog.next();
Bundle resultBundle = messageToBundle(msgArrived.getMessageId(),
msgArrived.getTopic(), msgArrived.getMessage());
// 关注下这个action，下面会用到
resultBundle.putString(MqttServiceConstants.CALLBACK_ACTION,
MqttServiceConstants.MESSAGE_ARRIVED_ACTION);
service.callbackToActivity(clientHandle, Status.OK, resultBundle);
}
}
复制代码
能够看到这个函数中调用了几个方法中的其中两个service.callbackToActivity(clientHandle, Status.OK, resultBundle);和deliverBacklog();，deliverBacklog()方法最后也是调用的service.callbackToActivity方法。因此直接看service.callbackToActivity：
// MqttService类：
void callbackToActivity(String clientHandle, Status status,
Bundle dataBundle) {
// 发送广播
Intent callbackIntent = new Intent(
MqttServiceConstants.CALLBACK_TO_ACTIVITY);
if (clientHandle != null) {
callbackIntent.putExtra(
MqttServiceConstants.CALLBACK_CLIENT_HANDLE, clientHandle);
}
callbackIntent.putExtra(MqttServiceConstants.CALLBACK_STATUS, status);
if (dataBundle != null) {
callbackIntent.putExtras(dataBundle);
}
LocalBroadcastManager.getInstance(this).sendBroadcast(callbackIntent);
}
复制代码
service.callbackToActivity方法其实就是发送广播，那谁来接收广播呢？其实接收广播的就在最开始的MqttAndroidClient，MqttAndroidClient继承自BroadcastReceiver，因此说MqttAndroidClient自己就是一个广播接收者，因此咱们来看它的onReceive方法：
// MqttAndroidClient类：
@Override
public void onReceive(Context context, Intent intent) {
Bundle data = intent.getExtras();
String handleFromIntent = data
.getString(MqttServiceConstants.CALLBACK_CLIENT_HANDLE);
if ((handleFromIntent == null)
|| (!handleFromIntent.equals(clientHandle))) {
return;
}
String action = data.getString(MqttServiceConstants.CALLBACK_ACTION);
// 判断消息的action类型
if (MqttServiceConstants.CONNECT_ACTION.equals(action)) {
connectAction(data);
} else if (MqttServiceConstants.CONNECT_EXTENDED_ACTION.equals(action)) {
connectExtendedAction(data);
} else if (MqttServiceConstants.MESSAGE_ARRIVED_ACTION.equals(action)) {
messageArrivedAction(data);
} else if (MqttServiceConstants.SUBSCRIBE_ACTION.equals(action)) {
subscribeAction(data);
} else if (MqttServiceConstants.UNSUBSCRIBE_ACTION.equals(action)) {
unSubscribeAction(data);
} else if (MqttServiceConstants.SEND_ACTION.equals(action)) {
// 发布成功与否的回调
sendAction(data);
} else if (MqttServiceConstants.MESSAGE_DELIVERED_ACTION.equals(action)) {
messageDeliveredAction(data);
} else if (MqttServiceConstants.ON_CONNECTION_LOST_ACTION
.equals(action)) {
connectionLostAction(data);
} else if (MqttServiceConstants.DISCONNECT_ACTION.equals(action)) {
disconnected(data);
} else if (MqttServiceConstants.TRACE_ACTION.equals(action)) {
traceAction(data);
} else {
mqttService.traceError(MqttService.TAG, "Callback action doesn't exist.");
}
}
复制代码
从代码和注释以及上面的deliverBacklog方法中能够知道，咱们如今须要关注的action为MESSAGE_ARRIVED_ACTION，因此就能够调用方法messageArrivedAction(data)：
// MqttAndroidClient类：
private void messageArrivedAction(Bundle data) {
if (callback != null) {
String messageId = data
.getString(MqttServiceConstants.CALLBACK_MESSAGE_ID);
String destinationName = data
.getString(MqttServiceConstants.CALLBACK_DESTINATION_NAME);
ParcelableMqttMessage message = data
.getParcelable(MqttServiceConstants.CALLBACK_MESSAGE_PARCEL);
try {
if (messageAck == Ack.AUTO_ACK) {
callback.messageArrived(destinationName, message);
mqttService.acknowledgeMessageArrival(clientHandle, messageId);
} else {
message.messageId = messageId;
callback.messageArrived(destinationName, message);
}
// let the service discard the saved message details
} catch (Exception e) {
// Swallow the exception
}
}
}
@Override
public void setCallback(MqttCallback callback) {
this.callback = callback;
}
复制代码
在messageArrivedAction方法中能够看到，咱们最后调用了callback回调了messageArrived方法，那么 callback经过上面下部分代码能够知道，其实这个callback就是咱们上一篇文章中所说的咱们初始化MqttAndroidClient后，经过方法setCallback设置的咱们本身定义的实现MqttCallback接口的回调类。
监听Broker返回的消息之发布消息成功与否
再看下sendAction(data)方法：
private void sendAction(Bundle data) {
IMqttToken token = getMqttToken(data);
// remove on delivery
simpleAction(token, data);
}
private void simpleAction(IMqttToken token, Bundle data) {
if (token != null) {
Status status = (Status) data
.getSerializable(MqttServiceConstants.CALLBACK_STATUS);
if (status == Status.OK) {
// 若是发布成功回调此方法
((MqttTokenAndroid) token).notifyComplete();
} else {
Exception exceptionThrown =
(Exception) data.getSerializable(MqttServiceConstants.CALLBACK_EXCEPTION);
// 发布失败回调
((MqttTokenAndroid) token).notifyFailure(exceptionThrown);
}
} else {
if (mqttService != null) {
mqttService.traceError(MqttService.TAG, "simpleAction : token is null");
}
}
}
复制代码
接下来再看一看发布成功回调的MqttTokenAndroid的notifyComplete函数：
// MqttTokenAndroid类：
void notifyComplete() {
synchronized (waitObject) {
isComplete = true;
waitObject.notifyAll();
if (listener != null) {
listener.onSuccess(this);
}
}
}
复制代码
这里又调用了listener.onSuccess(this)方法，那么这个listener是谁？其实listener就是咱们调用MqttAndroidClient类的publish发布的最后一个参数，即咱们自定义的监听发布消息是否发布成功的回调类。上面在MqttConnection类的publish方法中封装过MqttServiceConstants.SEND_ACTION的Bundle数据，而此数据是被MqttConnection类里的MqttConnectionListener携带。因此MqttConnectionListener里的onSuccess被调用时就会调用service.callbackToActivity，继而到sendBroadcast发送广播，最后调用sendAction方法，回调自定义的IMqttActionListener的实现类。而MqttConnectionListener里的onSuccess是在CommsCallback类里的fireActionEvent方法中，往上走就到CommsCallback类的了handleActionComplete和run()函数。
如今看是否是有点懵毕竟上面有两个 监听Broker返回的消息，一个是用来监听Broker发给客户端数据的监听，另外一个是客户端发布消息是否发布成功的监听而已。二者都是使用MqttActionListener，不过前者在MqttActionListener监听回调里最后调用的是自定义的MqttCallback回调而已。而且二者监听的位置不同，前者是在 MqttConnection类的connect时就已确认下来的，对于一个MQTT链接只会有一个，因此这个是一直用来监听数据的；然后者监听发布消息是否成功是每一个publish都须要传入的，并在MqttConnection类里的publish初始化。这么讲是否是就清晰一些啦。
哈哈，到此MQTT的publish发布以及接收Broker数据的源码分析也看完啦。
(注：如有什么地方阐述有误，敬请指正。)
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