Selective Consumer

Overview

Selective Consumer allows a message receiver to filter and consume only messages that match specific criteria, ignoring irrelevant messages on a shared channel.

Problem

How can a message consumer receive only messages it's interested in? When multiple types of messages flow through a shared channel, a consumer may only want to process messages that meet certain criteria. Processing all messages wastes resources and complicates the receiver logic.

Solution

Implement a Selective Consumer that specifies selection criteria when subscribing to a channel. The consumer receives only messages that match its filter criteria, while other messages pass to different consumers or are ignored.

Key Characteristics

• Filter Criteria: Specifies which messages to receive
• Selective Processing: Processes only relevant messages
• Resource Efficiency: Avoids processing unwanted messages
• Multiple Consumers: Different consumers have different criteria
• Expression-Based: Uses query or filter expressions
• Early Filtering: Messages filtered before delivery

When to Use

• Shared channels with heterogeneous message types
• Consumer only processes specific message categories
• Performance optimization through early filtering
• Multiple consumers with different interests
• Topic-based subscription models
• Event filtering in event-driven architectures
• Message prioritization scenarios

Implementation Considerations

• Filter Syntax: Choose expressive filter language
• Performance: Filter evaluation should be fast
• Message Headers: Place filterable data in headers
• Dynamic Filters: Allow runtime filter updates
• Unmatched Messages: Handle messages no consumer wants
• Filter Complexity: Balance power vs simplicity

Related Patterns

• Message Filter
• Content-Based Router
• Message
• Publish-Subscribe Channel
• Message Selector (messaging infrastructure feature)