Spring Integration - Basic Terms

Reference

Spring Integration Basic Terms
後篇: https://www.isaacnote.com/2018/10/spring-integration-channels.html 

Terms

org.springframework.integration.Message<T>

用來封裝訊息, 成員包含 MessageHeader 與 Payload

org.springframework.integration.MessageHeaders

MessageHeaders 是 immutable 的, 包含一些預設的 attribute: id, timestamp, correlation id, and priority

Payloads

用來裝 message body, 可以自訂 transformer 來傳遞封包

Message Channel

Message Channel 用來傳遞封包, 也用來 decouple producer 與 consumer.

Message Channel 有兩種模式: 

1. point to point, 一個封包只會被一個 consumer 收到
2. public/subscribe: 一個封包會被多個 consumer 收到

Message Endpoints

endpoint 泛指 Spring Integration 裡面的各種 component.

• Message Adapter: 資料可從外部系統透過 adapter 送進 Spring Integration
• Transformer: 轉換訊息
• Filter: 決定 Message 是否傳給 Message Channel
• Router: 透過 Message 的內容判斷要送給哪一個 Message Channel
• Splitter: 把一個 Message 切成好幾個轉送給不同適合的 Message Channel
• Aggregator: 把多個訊息合併成一個
• Service activator: Message Channel 與 Service instance 之間的介面

Example

spring-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:int="http://www.springframework.org/schema/integration"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration-5.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">
        <context:component-scan base-package="examples" />
        <int:channel id="input"/>
        <int:channel id="output">
            <int:queue capacity="10"/>
        </int:channel>
        <int:service-activator input-channel="input"
                           output-channel="output"
                           ref="messageHandler"/>
</beans>

examples/MessageHandler.java

@Component
public class MessageHandler {
    @ServiceActivator
    public String handleMessage(String message) {
        System.out.println("Received message: " + message);
        return "MESSAGE:" + message;
    }
}

examples/Application.java

public class Application {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring-context.xml");
        context.start();

        MessageChannel input = context.getBean("input", MessageChannel.class );
        PollableChannel output = context.getBean("output", PollableChannel.class );

        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextLine()) {
            input.send(MessageBuilder.withPayload(scanner.nextLine()).build());
        }
    }
}

Run, input message and send to MessageHandler to print