Message conversion involves transforming messages between various formats and representations as they are sent and received by applications. AWS SQS supports text-based payloads, and Spring Cloud AWS integrates with SQS, offering Spring’s familiar abstractions to handle the serialization and deserialization of text payloads to and from POJOs and records, with JSON as the default format. Let us delve into understanding Spring Cloud AWS v3 message conversion, focusing on how it manages serialization and deserialization of messages, including key use cases like POJO/record handling, custom ObjectMapper configuration, and deserializing to subclass or interface implementations.
1. Introduction
Spring Cloud AWS simplifies the integration of AWS services like SQS, SNS, and more in Spring Boot applications. You can find the official documentation for Spring Cloud AWS here. With AWS SDK v3, message handling, especially with JSON payloads, can be challenging. Spring Cloud AWS v3 provides support for converting messages to and from Java objects efficiently.
2. Dependencies
To start with Spring Cloud AWS v3, add the following dependencies to your pom.xml:
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-aws-messaging</artifactId>
<version>3.0.0</version>
</dependency>
<dependency>
<groupId>software.amazon.awssdk</groupId>
<artifactId>sqs</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
</dependency>
</dependencies>
The pom.xml defines a:
spring-cloud-starter-aws-messaging: Provides support for AWS messaging services.software.amazon.awssdk.sqs: The AWS SDK for working with SQS.jackson-databind: Jackson library for serializing and deserializing JSON objects.
3. Setting up the Local Test Environment
To avoid costs from using real AWS services, you can set up a local SQS service using tools like LocalStack. Add the following configurations to application.yml file present in the resources folder to point to the local SQS:
spring:
cloud:
aws:
sqs:
endpoint: http://localhost:4566
region: us-west-2
This YAML file helps to configure Spring Cloud AWS to use a local SQS endpoint instead of real AWS infrastructure.
4. Setting up the Queue Names
Define queue names in application.yml:
cloud:
aws:
messaging:
queues:
input-queue: my-input-queue
output-queue: my-output-queue
These queue names will be referenced when sending or receiving messages in the application.
5. Setting up the Application
Create a Spring Boot application that listens to messages on SQS. Start by creating an SQS listener:
@SqsListener("my-input-queue")
public void receiveMessage(MyMessage myMessage) {
// Process message
System.out.println("Received: " + myMessage);
}
The @SqsListener annotation tells Spring to listen to the specified SQS queue. The incoming message is automatically converted into the MyMessage object.
6. Processing POJOs and Records With Default Configuration
The default configuration uses Jackson to deserialize messages into POJOs. Below is an example of a POJO and how it gets processed:
public class MyMessage {
private String id;
private String content;
// Getters and Setters
}
When a message arrives in JSON format like this:
{
"id": "123",
"content": "Hello, World!"
}
It will be automatically converted to an instance of MyMessage.
7. Configuring a Custom Object Mapper
If you need custom serialization/deserialization behavior, you can configure a custom ObjectMapper:
@Bean
public ObjectMapper customObjectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
return objectMapper;
}
This custom ObjectMapper ignores unknown properties in the incoming JSON, preventing errors when extra fields are present.
8. Configuring Inheritance and Interfaces Deserialization
Handling deserialization for polymorphic types (like interfaces and inheritance) requires additional configuration. Consider the following class hierarchy:
public interface Message { }
public class TextMessage implements Message {
private String text;
// Getters and Setters
}
public class ImageMessage implements Message {
private String url;
// Getters and Setters
}
To deserialize based on the actual type, you can annotate the base class/interface with Jackson annotations:
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
@JsonSubTypes({
@JsonSubTypes.Type(value = TextMessage.class, name = "text"),
@JsonSubTypes.Type(value = ImageMessage.class, name = "image")
})
public interface Message { }
The @JsonTypeInfo and @JsonSubTypes annotations enable Jackson to determine which concrete class to deserialize based on a “type” property in the JSON.
9. Conclusion
Spring Cloud AWS v3 simplifies message conversion for AWS SQS, allowing developers to focus on processing business logic. With the default Jackson integration, POJO handling is seamless, and custom configurations enable more complex use cases, such as handling polymorphism and configuring custom mappers.
