前言
我们在Spring整合Mqtt简单使用的基础上继续分析。
代码示例
配置消息处理器
import java.util.UUID;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.integration.annotation.IntegrationComponentScan;
import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.integration.channel.DirectChannel;
import org.springframework.integration.config.EnableIntegration;
import org.springframework.integration.core.MessageProducer;
import org.springframework.integration.mqtt.core.DefaultMqttPahoClientFactory;
import org.springframework.integration.mqtt.core.MqttPahoClientFactory;
import org.springframework.integration.mqtt.inbound.MqttPahoMessageDrivenChannelAdapter;
import org.springframework.integration.mqtt.outbound.MqttPahoMessageHandler;
import org.springframework.integration.mqtt.support.DefaultPahoMessageConverter;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.MessageHandler;
@Configuration
@IntegrationComponentScan
@EnableIntegration
public class MqttClientConfig {
/**
* 连接工厂.
*/
@Bean
public MqttPahoClientFactory mqttClientFactory() {
DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
mqttConnectOptions.setUserName("test1");
mqttConnectOptions.setPassword("123456".toCharArray());
mqttConnectOptions.setServerURIs(new String[]{"tcp://xxx:1883"});
mqttConnectOptions.setKeepAliveInterval(2);
mqttConnectOptions.setAutomaticReconnect(true);
factory.setConnectionOptions(mqttConnectOptions);
return factory;
}
private String createClientId() {
return UUID.randomUUID().toString();
}
/**
* 配置client,发布.
*/
@Bean
@ServiceActivator(inputChannel = "mqttOutboundChannel")
public MessageHandler mqttOutbound() {
MqttPahoMessageHandler messageHandler = new MqttPahoMessageHandler(
createClientId(), mqttClientFactory());
messageHandler.setAsync(true);
messageHandler.setDefaultQos(2);
messageHandler.setDefaultRetained(false); //不保留消息
return messageHandler;
}
@Bean
public MessageChannel mqttOutboundChannel() {
return new DirectChannel();
}
//接收通道
@Bean
public MessageChannel mqttInputChannel() {
return new DirectChannel();
}
/**
* 配置client,监听的topic.
*/
@Bean
public MessageProducer inbound() {
String[] topics = {"first_topic"};
MqttPahoMessageDrivenChannelAdapter adapter =
new MqttPahoMessageDrivenChannelAdapter(createClientId(),
mqttClientFactory(), topics);
adapter.setCompletionTimeout(3_000);
adapter.setConverter(new DefaultPahoMessageConverter());
adapter.setQos(2);
adapter.setOutputChannel(mqttInputChannel());
return adapter;
}
/**
* 消息处理器
*/
@Bean
@ServiceActivator(inputChannel = "mqttInputChannel")
public MessageHandler handler() {
return (message -> {
String topic = message.getHeaders().get("mqtt_receivedTopic").toString();
String payload = message.getPayload().toString();
System.out.println("消息主题：" + topic);
System.out.println("消息内容：" + payload);
});
}
}
配置消息通道MessageChannel和消息处理器，消息通道有两个，一个用来发送消息，一个用来接收消息。
配置消息网关
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.integration.mqtt.support.MqttHeaders;
import org.springframework.messaging.handler.annotation.Header;
import org.springframework.stereotype.Component;
@Component
@MessagingGateway(defaultRequestChannel = "mqttOutboundChannel")
public interface MqttGateway {
void sendToMqtt(String data, @Header(MqttHeaders.TOPIC) String topic);
}
加上@Component注解是为了IDE不报错，不加也不影响功能。
客户端使用
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class TestSpringMqtt {
public static void main(String[] args) {
// 创建容器上下文
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(MqttClientConfig.class);
MqttGateway mqttGateway = (MqttGateway) context.getBean("mqttGateway");
// 获取消息网关Bean对象并发送消息
mqttGateway.sendToMqtt("hello", "first_topic");
}
}
原理分析
@IntegrationComponentScan注解
先来分析@IntegrationComponentScan注解，它会导入IntegrationComponentScanRegistrar配置类。
public class IntegrationComponentScanRegistrar implements ImportBeanDefinitionRegistrar,
ResourceLoaderAware, EnvironmentAware {
private final Map<TypeFilter, ImportBeanDefinitionRegistrar> componentRegistrars =
new HashMap<TypeFilter, ImportBeanDefinitionRegistrar>();
// 过滤类型为@MessagingGateway注解，会交给MessagingGatewayRegistrar来处理
public IntegrationComponentScanRegistrar() {
this.componentRegistrars.put(new AnnotationTypeFilter(MessagingGateway.class, true),
new MessagingGatewayRegistrar());
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
Map<String, Object> componentScan =
importingClassMetadata.getAnnotationAttributes(IntegrationComponentScan.class.getName());
Collection<String> basePackages = getBasePackages(importingClassMetadata, registry);
if (basePackages.isEmpty()) {
basePackages = Collections.singleton(ClassUtils.getPackageName(importingClassMetadata.getClassName()));
}
ClassPathScanningCandidateComponentProvider scanner =
new ClassPathScanningCandidateComponentProvider(false, this.environment) {
@Override
protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
return beanDefinition.getMetadata().isIndependent()
&& !beanDefinition.getMetadata().isAnnotation();
}
};
filter(registry, componentScan, scanner); // NOSONAR - never null
scanner.setResourceLoader(this.resourceLoader);
// 开始扫描
for (String basePackage : basePackages) {
Set<BeanDefinition> candidateComponents = scanner.findCandidateComponents(basePackage);
for (BeanDefinition candidateComponent : candidateComponents) {
if (candidateComponent instanceof AnnotatedBeanDefinition) {
for (ImportBeanDefinitionRegistrar registrar : this.componentRegistrars.values()) {
// 交给具体的注册器来处理，这里就是MessagingGatewayRegistrar
registrar.registerBeanDefinitions(((AnnotatedBeanDefinition) candidateComponent).getMetadata(),
registry);
}
}
}
}
}
}
此注解作用类似于@ComponentScan注解，会扫描包含@MessagingGateway注解的Class，并注册到容器中。继续分析MessagingGatewayRegistrar
public class MessagingGatewayRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
if (importingClassMetadata != null && importingClassMetadata.isAnnotated(MessagingGateway.class.getName())) {
Map<String, Object> annotationAttributes =
importingClassMetadata.getAnnotationAttributes(MessagingGateway.class.getName());
BeanDefinitionReaderUtils.registerBeanDefinition(this.parse(annotationAttributes), registry);
}
}
public BeanDefinitionHolder parse(Map<String, Object> gatewayAttributes) {
// 创建具体的BeanDefinition
String defaultPayloadExpression = (String) gatewayAttributes.get("defaultPayloadExpression");
// 核心，接口的具体实现类为GatewayProxyFactoryBean
BeanDefinitionBuilder gatewayProxyBuilder =
BeanDefinitionBuilder.genericBeanDefinition(GatewayProxyFactoryBean.class);
AbstractBeanDefinition beanDefinition = gatewayProxyBuilder.getBeanDefinition();
beanDefinition.addMetadataAttribute(new BeanMetadataAttribute(IntegrationConfigUtils.FACTORY_BEAN_OBJECT_TYPE,
serviceInterface));
return new BeanDefinitionHolder(beanDefinition, id);
}
}
使用GatewayProxyFactoryBean类来作为接口的具体实现。
public class GatewayProxyFactoryBean extends AbstractEndpoint
implements TrackableComponent, FactoryBean<Object>, MethodInterceptor, BeanClassLoaderAware {
protected void onInit() {
synchronized (this.initializationMonitor) {
// 创建动态代理对象，这里的serviceInterface就是我们定义的MqttGateway，
// 拦截器就是GatewayProxyFactoryBean自身
this.serviceProxy = new ProxyFactory(this.serviceInterface, this).getProxy(this.beanClassLoader);
}
}
@Override
public Object getObject() {
if (this.serviceProxy == null) {
this.onInit();
}
// 返回创建的代理对象
return this.serviceProxy;
}
}
GatewayProxyFactoryBean使用动态代理(底层是Cglib或JDK)创建一个代理对象，拦截器就是自身，所以当我们调用MqttGateway的sendToMqtt()方法时，
就会被拦截到GatewayProxyFactoryBean的invoke()方法。
发送Mqtt消息流程分析
从GatewayProxyFactoryBean类的invoke()方法开始
@Override
@Nullable
public Object invoke(final MethodInvocation invocation) throws Throwable { // NOSONAR
// 继续执行
return doInvoke(invocation, true);
}
@Nullable
private Object invokeGatewayMethod(MethodInvocation invocation, boolean runningOnCallerThread) {
Method method = invocation.getMethod();
// 根据method找到对应的MethodInvocationGateway
MethodInvocationGateway gateway = this.gatewayMap.get(method);
// 发送消息并接收响应
response = sendOrSendAndReceive(invocation, gateway, shouldReturnMessage, shouldReply);
// 处理返回值类型
return response(gateway.returnType, shouldReturnMessage, response);
}
具体发送的处理会交给MethodInvocationGateway来处理，进入它的父类MessagingGatewaySupport的send()方法
protected void send(Object object) {
// 根据@MessagingGateway注解中配置的defaultRequestChannel属性值从容器中获取到消息通道Bean对象
MessageChannel channel = getRequestChannel();
try {
this.messagingTemplate.convertAndSend(channel, object, this.historyWritingPostProcessor);
}
}
这个消息通道对象就是我们在MqttClientConfig配置类中声明的如下Bean，具体类型为DirectChannel。
@Bean
public MessageChannel mqttOutboundChannel() {
return new DirectChannel();
}
我们继续分析messagingTemplate的convertAndSend()方法，最终进入GenericMessagingTemplate的doSend()方法
protected final void doSend(MessageChannel channel, Message<?> message, long timeout) {
Message<?> messageToSend = message;
// 委托给channel对象来发送消息，这里的channel具体类型为上面定义的DirectChannel
boolean sent = (timeout >= 0 ? channel.send(messageToSend, timeout) : channel.send(messageToSend));
}
进入DirectChannel的父类AbstractMessageChannel的send()方法
@Override // NOSONAR complexity
public boolean send(Message<?> messageArg, long timeout) {
Message<?> message = messageArg;
try {
// 消息类型转换
message = convertPayloadIfNecessary(message);
// 实际发送消息
sent = doSend(message, timeout);
return sent;
}
}
@Override
protected boolean doSend(Message<?> message, long timeout) {
try {
//这里的MessageDispatcher(消息分发器)类型为UnicastingDispatcher
return getRequiredDispatcher().dispatch(message);
}
}
DirectChannel中定义的消息分发器类型为UnicastingDispatcher，这是一个单播分发器，表示这条消息只会由一个消息处理器来处理，区别于广播分发器BroadcastingDispatcher。
private boolean doDispatch(Message<?> message) {
// 先尝试优化处理，如果只有一个消息处理器的话，直接交给它处理
if (tryOptimizedDispatch(message)) {
return true;
}
boolean success = false;
// 有多个消息处理器的情况
Iterator<MessageHandler> handlerIterator = getHandlerIterator(message);
List<RuntimeException> exceptions = null;
// 有一个处理成功就退出循环
while (!success && handlerIterator.hasNext()) {
MessageHandler handler = handlerIterator.next();
try {
// 消息处理器处理消息
handler.handleMessage(message);
success = true; // we have a winner.
}
}
return success;
}
其实这里的消息处理器就是我们在MqttClientConfig配置类中定义的如下Bean
/**
* 配置client,发布.
*/
@Bean
@ServiceActivator(inputChannel = "mqttOutboundChannel")
public MessageHandler mqttOutbound() {
MqttPahoMessageHandler messageHandler = new MqttPahoMessageHandler(
createClientId(), mqttClientFactory());
messageHandler.setAsync(true);
messageHandler.setDefaultQos(2);
messageHandler.setDefaultRetained(false); //不保留消息
return messageHandler;
}
继续分析MqttPahoMessageHandler是如何处理消息的
public class MqttPahoMessageHandler extends AbstractMqttMessageHandler
implements MqttCallback, ApplicationEventPublisherAware {
@Override
protected void handleMessageInternal(Message<?> message) throws Exception {
Object mqttMessage = this.converter.fromMessage(message, Object.class);
String topic = this.topicProcessor.processMessage(message);
// 发布消息
publish(topic == null ? this.defaultTopic : topic, mqttMessage, message);
}
@Override
protected void publish(String topic, Object mqttMessage, Message<?> message) throws Exception {
// 根据MqttPahoClientFactory创建MqttAsyncClient对象，向Mqtt服务器发送Mqtt消息
IMqttDeliveryToken token = checkConnection()
.publish(topic, (MqttMessage) mqttMessage);
}
}
至此Mqtt消息发送的流程就结束了，总结一下
- 定义MqttGateway接口，包含@MessagingGateway注解
- @IntegrationComponentScan会引入IntegrationComponentScanRegistrar配置类，扫描包含@MessagingGateway注解的Class，
使用GatewayProxyFactoryBean来实现此接口。 - GatewayProxyFactoryBean创建动态代理对象，拦截发送Mqtt消息的处理，委托给对应的MessageChannel(消息通道)，
此消息通道是通过@MessagingGateway注解的defaultRequestChannel属性来配置的。 - 消息通道对象委托给消息分发器来处理，具体为UnicastingDispatcher(单播分发器)
- 消息分发器会查找到多个对应的消息处理器(MessageHandler)，交给它们处理
但Spring是什么时候向消息分发器中添加消息处理器的呢，这个就涉及到@ServiceActivator注解的功能了。而@ServiceActivator注解功能的开启需要@EnableIntegration注解，
所以接下来继续分析@EnableIntegration注解。
@EnableIntegration注解
从注解的名称可以简单看出来，开启集成功能，它会引入IntegrationRegistrar配置类。
public class IntegrationRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(@Nullable AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
registerImplicitChannelCreator(registry);
registerDefaultConfiguringBeanFactoryPostProcessor(registry);
registerIntegrationConfigurationBeanFactoryPostProcessor(registry);
if (importingClassMetadata != null) {
// 向容器中注册MessagingAnnotationPostProcessor
registerMessagingAnnotationPostProcessors(importingClassMetadata, registry);
}
}
}
此配置类会向容器中注册很多Bean，我们只关注MessagingAnnotationPostProcessor，这是一个BeanPostProcessor。
public class MessagingAnnotationPostProcessor implements BeanPostProcessor, BeanFactoryAware, InitializingBean,
SmartInitializingSingleton {
@Override
public void afterPropertiesSet() {
((BeanDefinitionRegistry) this.beanFactory).registerBeanDefinition(
IntegrationContextUtils.DISPOSABLES_BEAN_NAME,
BeanDefinitionBuilder.genericBeanDefinition(Disposables.class, Disposables::new)
.getRawBeanDefinition());
this.postProcessors.put(Filter.class, new FilterAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(Router.class, new RouterAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(Transformer.class, new TransformerAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(ServiceActivator.class, new ServiceActivatorAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(Splitter.class, new SplitterAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(Aggregator.class, new AggregatorAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(InboundChannelAdapter.class,
new InboundChannelAdapterAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(BridgeFrom.class, new BridgeFromAnnotationPostProcessor(this.beanFactory));
this.postProcessors.put(BridgeTo.class, new BridgeToAnnotationPostProcessor(this.beanFactory));
Map<Class<? extends Annotation>, MethodAnnotationPostProcessor<?>> customPostProcessors =
setupCustomPostProcessors();
if (!CollectionUtils.isEmpty(customPostProcessors)) {
this.postProcessors.putAll(customPostProcessors);
}
}
}
可以看到，它会处理很多注解类型的解析，包括我们用到的@ServiceActivator注解。
@Override
public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
Assert.notNull(this.beanFactory, "BeanFactory must not be null");
Class<?> beanClass = AopUtils.getTargetClass(bean);
// 遍历每个方法，解析上述注解
ReflectionUtils.doWithMethods(beanClass,
method -> doWithMethod(method, bean, beanName, beanClass),
ReflectionUtils.USER_DECLARED_METHODS);
return bean;
}
此方法会在Bean初始化之后调用，解析上述的所有注解
protected void processAnnotationTypeOnMethod(Object bean, String beanName, Method method,
Class<? extends Annotation> annotationType, List<Annotation> annotations) {
// 根据对应的注解类型找到对应的注解处理器，
// 以@ServiceActivator注解为例，得到的postProcessor类型就是ServiceActivatorAnnotationPostProcessor
MethodAnnotationPostProcessor<?> postProcessor =
MessagingAnnotationPostProcessor.this.postProcessors.get(annotationType);
if (postProcessor != null && postProcessor.shouldCreateEndpoint(method, annotations)) {
Method targetMethod = method;
if (this.initialized) {
// 处理此Method并注册Endpoint
postProcessMethodAndRegisterEndpointIfAny(bean, beanName, method, annotationType, annotations,
postProcessor, targetMethod);
}
}
}
继续跟进去
private void postProcessMethodAndRegisterEndpointIfAny(Object bean, String beanName, Method method,
Class<? extends Annotation> annotationType, List<Annotation> annotations,
MethodAnnotationPostProcessor<?> postProcessor, Method targetMethod) {
// 以@ServiceActivator注解为例，处理之后得到result为EventDrivenConsumer类型，是AbstractEndpoint的子类
Object result = postProcessor.postProcess(bean, beanName, targetMethod, annotations);
if (result instanceof AbstractEndpoint) {
// 将这个创建的endpoint对象实例注册到Bean容器中并初始化
AbstractEndpoint endpoint = (AbstractEndpoint) result;
String endpointBeanName = generateBeanName(beanName, method, annotationType);
endpoint.setBeanName(endpointBeanName);
// 作为单例注册到容器中
getBeanFactory().registerSingleton(endpointBeanName, endpoint);
// Bean初始化
getBeanFactory().initializeBean(endpoint, endpointBeanName);
}
}
接下来再看一下EventDrivenConsumer的作用
public class EventDrivenConsumer extends AbstractEndpoint implements IntegrationConsumer {
@Override
protected void doStart() {
// 将消息处理器添加到消息通道中，具体来说就是添加到消息分发器中
this.inputChannel.subscribe(this.handler);
if (this.handler instanceof Lifecycle) {
((Lifecycle) this.handler).start();
}
}
}
简单总结一下
- @EnableIntegration注解开启对@ServiceActivator注解的处理。
- @ServiceActivator注解将此消息处理器添加到配置的消息通道中，每个消息通道都包含一个消息分发器，实际上是添加到消息分发器中。
消息通道是通过@ServiceActivator注解的inputChannel属性来配置的。
接收Mqtt消息流程分析
接收消息是由我们配置类中定义的MqttPahoMessageDrivenChannelAdapter来处理的
/**
* 配置client,监听的topic.
*/
@Bean
public MessageProducer inbound() {
String[] topics = {"first_topic"};
MqttPahoMessageDrivenChannelAdapter adapter =
new MqttPahoMessageDrivenChannelAdapter(createClientId(),
mqttClientFactory(), topics);
adapter.setCompletionTimeout(3_000);
adapter.setConverter(new DefaultPahoMessageConverter());
adapter.setQos(2);
adapter.setOutputChannel(mqttInputChannel());
return adapter;
}
它是一个MqttCallback，重写了messageArrived()方法，如果不了解MqttCallback可以查看Spring整合Mqtt简单使用。
@Override
public void messageArrived(String topic, MqttMessage mqttMessage) {
Message<?> message = this.getConverter().toMessage(topic, mqttMessage);
try {
// 发送消息
sendMessage(message);
}
}
protected void sendMessage(Message<?> messageArg) {
Message<?> message = messageArg;
MessageChannel messageChannel = getOutputChannel();
// 会委托给MessageChannel来发送
this.messagingTemplate.send(messageChannel, message);
}
MessageChannel(消息通道)委托给自身的消息分发器来处理，找到对应的消息处理器
/**
* 消息处理器
*/
@Bean
@ServiceActivator(inputChannel = "mqttInputChannel")
public MessageHandler handler() {
return (message -> {
String topic = message.getHeaders().get("mqtt_receivedTopic").toString();
String payload = message.getPayload().toString();
System.out.println("消息主题：" + topic);
System.out.println("消息内容：" + payload);
});
}
至此接收Mqtt消息的的流程就结束了。
总结
Spring整合Mqtt协议使用到了spring-integration框架，它内部又依赖spring-messaging框架。Spring中消息处理一共有3种角色(实际上不止3种，这里我们仅用到了3种)
- 消息生产者(MessageProducer)，我们配置的MqttPahoMessageDrivenChannelAdapter和MqttGateway接口都是这种角色，内部需要关联一个消息通道。
- 消息处理器(MessageHandler)，我们配置的MqttPahoMessageHandler和lambda表达式实现都是这种角色。
- 消息通道(MessageChannel)，内部包含一个消息分发器，消息分发器中包含多个消息处理器。
通过@ServiceActivator注解将具体的消息处理器添加到消息通道中。消息生产者生成一个消息，通过内部的消息通道将消息分发给对应的消息处理器。
注意，这里所说的消息为Spring-messaging框架中的通用消息，和Mqtt消息没有关系。
Mqtt消息发送的流程为：
- MqttGateway生成一个Spring消息，通过消息通道找到对应的消息处理器MqttPahoMessageHandler，它会将Mqtt消息发送给Mqtt服务器。
Mqtt消息接收的流程为：
- MqttPahoMessageDrivenChannelAdapter是一个Mqtt消息的监听器，当接收到一个Mqtt消息后，生成一个Spring消息，通过消息通道找到对应的消息处理器，
就是我们自己定义的MqttClientConfig配置类中的handler()方法。