跟踪mqttv3源码（二）

对于spring-mqtt.xml中的标签：

<int-mqtt:message-driven-channel-adapter>

<int-mqtt:outbound-channel-adapter>

<int:channel>

<int:transformer>

<int:service-activator>

<int:outbound-channel-adapter>

了解Spring自定义标签的应该都知道标签的构建过程：

1、首先我们进入spring-integration-mqtt-4.3.5 --->META-INF路径查看spring.handlers

http\://www.springframework.org/schema/integration/mqtt=org.springframework.integration.mqtt.config.xml.MqttNamespaceHandler

得知命名处理类MqttNamespaceHandler，进入config/xml :

public class MqttNamespaceHandler extends AbstractIntegrationNamespaceHandler {

    @Override
    public void init() {
        this.registerBeanDefinitionParser("message-driven-channel-adapter",  new MqttMessageDrivenChannelAdapterParser());
        this.registerBeanDefinitionParser("outbound-channel-adapter", new MqttOutboundChannelAdapterParser());
    }

}

public class MqttMessageDrivenChannelAdapterParser extends AbstractChannelAdapterParser {

    @Override
    protected AbstractBeanDefinition doParse(Element element, ParserContext parserContext, String channelName) {
　　　　 //包装类MqttPahoMessageDrivenChannelAdapter
        BeanDefinitionBuilder builder = BeanDefinitionBuilder
                .genericBeanDefinition(MqttPahoMessageDrivenChannelAdapter.class);
　　　　
　　　　 //用类MqttParserUtils设置builder属性：url、client-id、client-factory、converter、send-timeout
        MqttParserUtils.parseCommon(element, builder, parserContext);
　　　　 //解析spring-mqtt.xml中配置的属性topics、qos、recovery-interval
        builder.addConstructorArgValue(element.getAttribute("topics"));
        builder.addPropertyReference("outputChannel", channelName);
        IntegrationNamespaceUtils.setReferenceIfAttributeDefined(builder, element, "error-channel");
        IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "qos");
        IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "recovery-interval");

        return builder.getBeanDefinition();
    }

}

查看MqttPahoMessageDrivenChannelAdapter：builder.addPropertyReference("outputChannel", channelName);

跟踪channelName,进入AbstractChannelAdapterParser.parseInternal()可以看到channelName来源于element；

同理进入IntegrationNamespaceHandler，找到registerBeanDefinitionParser("service-activator", new ServiceActivatorParser());跟踪AbstractDelegatingConsumerEndpointParser-->AbstractConsumerEndpointParser：

protected String getInputChannelAttributeName() {
        return "input-channel";
}

String inputChannelAttributeName = this.getInputChannelAttributeName();
String inputChannelName = element.getAttribute(inputChannelAttributeName);
builder.addPropertyValue("inputChannelName", inputChannelName);

然后查看spring.tooling就可以得知标签int-mqtt的来源:

# Tooling related information for the integration mqtt namespace
http\://www.springframework.org/schema/integration/mqttadapter@name=integration mqtt Namespace
http\://www.springframework.org/schema/integration/mqttadapter@prefix=int-mqtt
http\://www.springframework.org/schema/integration/mqttadapter@icon=org/springframework/integration/config/xml/spring-integration-mqtt.gif

跟踪进spring-integration-4.3.xsd，可以看到标签<xsd:element service-activator>包含inputOutputChannelGroup：

    <xsd:element name="service-activator">
        <xsd:annotation>
            <xsd:documentation>
                Defines an endpoint for the 'org.springframework.integration.handler.ServiceActivatingHandler'
                for exposing any bean reference as a service that
                receives request Messages
                from an 'input-channel' and may send reply
                Messages to an 'output-channel'. The 'ref' may point to an instance
                that
                has either a single public method or a method with the
                @ServiceActivator annotation. Otherwise, the 'method'
                attribute
                should be provided along with 'ref'.
            </xsd:documentation>
        </xsd:annotation>
        <xsd:complexType>
            <xsd:complexContent>
                <xsd:extension base="serviceActivatorType">
                    <xsd:attributeGroup ref="inputOutputChannelGroup" />
                </xsd:extension>
            </xsd:complexContent>
        </xsd:complexType>
    </xsd:element>

查看标签<xsd:attributeGroup name="inputOutputChannelGroup">可以看到包含output-channel、input-channel、send-timeout、order：

<xsd:attributeGroup name="inputOutputChannelGroup">
        <xsd:attribute name="output-channel" type="xsd:string">
            <xsd:annotation>
                <xsd:appinfo>
                    <tool:annotation kind="ref">
                        <tool:expected-type type="org.springframework.messaging.MessageChannel" />
                    </tool:annotation>
                </xsd:appinfo>
                <xsd:documentation>
                Identifies the Message channel where Message will be sent after it's being processed by this endpoint
                </xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="send-timeout" type="xsd:string">
            <xsd:annotation>
                <xsd:documentation>
                    Specify the maximum amount of time in milliseconds to wait when sending a reply
                    Message to the output channel. Defaults to '-1' - blocking indefinitely.
                    It is applied only if the output channel has some 'sending' limitations, e.g. QueueChannel with
                    fixed a 'capacity'. In this case a MessageDeliveryException is thrown. The 'send-timeout'
                    is ignored in case of AbstractSubscribableChannel implementations.
                </xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="input-channel" type="xsd:string">
            <xsd:annotation>
                <xsd:appinfo>
                    <tool:annotation kind="ref">
                        <tool:expected-type type="org.springframework.messaging.MessageChannel" />
                    </tool:annotation>
                </xsd:appinfo>
                <xsd:documentation>
                The receiving Message channel of this endpoint
                </xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="order" type="xsd:string">
            <xsd:annotation>
                <xsd:documentation><![CDATA[
Specifies the order for invocation when this endpoint is connected as a
subscriber to a channel. This is particularly relevant when that channel
is using a "failover" dispatching strategy. It has no effect when this
endpoint itself is a Polling Consumer for a channel with a queue.
                    ]]></xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attributeGroup ref="smartLifeCycleAttributeGroup"/>
    </xsd:attributeGroup>

可以看到配置文件中：org.springframework.integration.mqtt.core.DefaultMqttPahoClientFactory用来配置通信基础信息

将DefaultMqttPahoClientFactory注入到类org.springframework.integration.mqtt.outbound.MqttPahoMessageHandler，类中messageArrived()方法用来获取消息