在Spring Integration下使用Paho接收二进制MQTT消息

Question

I have this code that receives MQTT messages under Spring Integration 5.0.x / Boot 2.0. It works fine for text messages, but when I try to process binary messages it fails because a conversion to String happens and this corrupts the content (in this case: a png image file).

How can I receive the message untampered ?

I tried to setBytesMessageMapper on DefaultPahoMessageConverter , but this didn't change a thing. When I download the messages content using mqtt.fx I can proof that the binary content was set correctly, so I am sure this is a problem on the receiving end.

@Bean
public MessageProducer inbound() {
    MqttPahoMessageDrivenChannelAdapter adapter = new MqttPahoMessageDrivenChannelAdapter("tcp://iot.eclipse.org:1883",
                "foo", "bar");
    adapter.setCompletionTimeout(5000);
    DefaultPahoMessageConverter converter = new DefaultPahoMessageConverter();
    adapter.setConverter(converter);
    adapter.setQos(1);
    adapter.setOutputChannel(mqttInputChannel());
    return adapter;
}
...
@Bean
@ServiceActivator(inputChannel = "mqttInputChannel")
public MessageHandler handler() {
    return new MessageHandler() {

        @Override
        public void handleMessage(Message<?> message) throws MessagingException {
            System.out.println("message received on " + new Date());        
            Object payload = message.getPayload();
            ...
    };
}

Answer 1

Set the payloadAsBytes property on the converter to true ...

/**
 * True if the converter should not convert the message payload to a String.
 * Ignored if a {@link BytesMessageMapper} is provided.
 *
 * @param payloadAsBytes The payloadAsBytes to set.
 * @see #setBytesMessageMapper(BytesMessageMapper)
 */
public void setPayloadAsBytes(boolean payloadAsBytes) {
    this.payloadAsBytes = payloadAsBytes;
}