A Spring Boot 3 application that serves as a gateway for Server-Sent Events (SSE) from multiple backend services. This service aggregates real-time events from various sources and provides unified endpoints for clients to consume these streams.

The SSE Gateway acts as a proxy and aggregator for multiple SSE endpoints, providing both public and secured access to real-time event streams.

• Java 21 or higher
• Node.js (for mock servers)
• Gradle (included as wrapper)

The easiest way to run the complete system is using the provided start script:

./start-all.sh

This script will:

• Check and install npm dependencies for mock servers
• Start three mock SSE servers on ports 8081, 8082, 8083
• Start the SSE Gateway on port 8080
• Display all available endpoints and example usage

cd mock-sse-servers
npm install
npm run start-all

This starts:

• Account Service on port 8081
• Payment Service on port 8082
• Customer Service on port 8083

./gradlew bootRun

Or with a specific profile:

./gradlew bootRun --args='--spring.profiles.active=local'

./gradlew build

The application uses Spring Boot configuration with the prefix sse-gateway. Configuration can be set in application.yaml or application-local.yaml.

sse-gateway:
  debug: false                    # Enable debug logging
  security: false                 # Enable/disable JWT security
  endpoints: []                   # List of public SSE endpoints
  secured-endpoints: []           # List of secured SSE endpoints (requires JWT)

Each endpoint is configured with:

• name: Unique identifier for the endpoint
• url: Backend SSE service URL
• filter-params: List of allowed query parameters

Example endpoint configuration:

sse-gateway:
  endpoints:
    - name: account-low-balance
      url: http://localhost:8081/accounts/low-balance-alerts
      filter-params:
        - customerId
        - currency
    - name: account-transactions
      url: http://localhost:8081/accounts/transaction-events
      filter-params:
        - customerId
        - currency
        - minAmount
    - name: payment-transactions
      url: http://localhost:8082/transactions/sse
      filter-params:
        - customerId
        - currency
        - limit
    - name: high-value-transactions
      url: http://localhost:8082/transactions/high-value
      filter-params:
        - minAmount
        - currency
    - name: customer-activity
      url: http://localhost:8083/customers/activity
      filter-params:
        - customerId
        - activityType
    - name: security-alerts
      url: http://localhost:8083/customers/security-alerts
      filter-params:
        - severity
        - customerId

When sse-gateway.security: true, the secured endpoints require JWT authentication. You must also configure the JWT issuer URI:

sse-gateway:
  security: true
  secured-endpoints:
    - name: customer-profile-events
      url: http://localhost:8083/customers/profile-events
      filter-params:
        - profileType
    - name: account-private-events
      url: http://localhost:8081/accounts/private-events
      filter-params:
        - currency

spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          issuer-uri: https://your-auth-server.com  # Required when security is enabled

Standard Spring Boot properties are also available:

server:
  port: 8080

spring:
  application:
    name: sse-gateway-services

management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics

• GET /public/events - Access public SSE streams without authentication
• GET /actuator/health - Health check endpoint
• GET /actuator/info - Application information
• GET /actuator/metrics - Metrics endpoint

• GET /events - Access secured SSE streams with JWT authentication

• sources: Comma-separated list of endpoint names to subscribe to
• Additional parameters as defined in endpoint filter-params

Public access:

curl "http://localhost:8080/public/events?sources=account-transactions,payment-transactions&customerId=cust123&currency=USD"

Secured access (when security enabled):

curl -H "Authorization: Bearer <JWT_TOKEN>" "http://localhost:8080/events?sources=customer-profile-events,account-private-events&currency=USD"

Uses configuration from application.yaml with production-ready settings.

Uses application-local.yaml with:

• Debug logging enabled
• H2 in-memory database
• OpenTelemetry disabled