Spring integration: filters

Filters are used to take decision like whether the message should be dropped or carry forward to a message channel.

If the message is accepted by a filter, then it is transferred to the output channel, else it is discarded.

 

How to define a filter?

You can define a filter using @Filter annotation. A method annotated with @Filter may accept a parameter of type Message or of the expected Message payload's type. The return type of the annotated method must be a boolean or Boolean.

 

Example

@Filter(inputChannel = "inputChannel", outputChannel = "secretChannel")
boolean filter(Message<?> message) {
	String msg = message.getPayload().toString();

	return msg.contains("secret");
}

 

Can a filter is capable of producing and consuming messages?

Yes, a filter is capable of producing and consuming messages.

 

Find the below working application.

 

Step 1: Create new maven project 'filter-demo'

 

Step 2: Update pom.xml with following dependencies.

 

pom.xml

 

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>filter-demo</artifactId>
	<version>1</version>

	<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.0</version>
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-integration</artifactId>
		</dependency>

	</dependencies>

</project>

 

Step 3: Define gateway.

 

CustomGateway.java

package com.sample.app.gateway;

import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.messaging.Message;

@MessagingGateway
public interface CustomGateway {

	@Gateway(requestChannel = "inputChannel")
	public void print(Message<?> message);

}

 

Step 4: Define consumer endpoint.

 

ConsumerEndpoint.java

package com.sample.app.endpoints;

import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.messaging.Message;
import org.springframework.stereotype.Component;

@Component
public class ConsumerEndpoint {

	@ServiceActivator(inputChannel = "secretChannel")
	public void consumeStringMessage(Message<String> message) {
		System.out.println("Received message from secretChannel : " + message.getPayload());
	}
}

Step 5: Define main application class.

 

App.java

package com.sample.app;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.integration.annotation.Filter;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.messaging.Message;

import com.sample.app.gateway.CustomGateway;

@SpringBootApplication
@Configuration
public class App {

	@Filter(inputChannel = "inputChannel", outputChannel = "secretChannel")
	boolean filter(Message<?> message) {
		String msg = message.getPayload().toString();

		return msg.contains("secret");
	}

	@Autowired
	private CustomGateway customGateway;

	public static void main(String[] args) {
		SpringApplication.run(App.class, args);
	}

	@Bean
	public CommandLineRunner demo() {
		return (args) -> {

			for (int i = 0; i < 10; i++) {
				Message<?> message = null;
				if (i % 2 == 0) {
					message = MessageBuilder.withPayload("secret message " + i).setHeader("messageType", "secret")
							.build();
				} else if (i % 3 == 0) {
					message = MessageBuilder.withPayload("public message " + i).setHeader("messageType", "public")
							.build();
				} else {
					message = MessageBuilder.withPayload("Generic message " + i).setHeader("messageType", "public")
							.build();
				}

				customGateway.print(message);
			}

		};
	}

}

Project structure looks like below.

Run App.java, you will see below messages in console.

Received message from secretChannel : secret message 0
Received message from secretChannel : secret message 2
Received message from secretChannel : secret message 4
Received message from secretChannel : secret message 6
Received message from secretChannel : secret message 8

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/spring-integration/filter-demo

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