TopicHelper.java

Overview

`TopicHelper.java` is a utility class designed to provide helper methods for rendering Kafka topic information in a human-readable string format. It is part of the Apache Camel Kafka component's consumer support package and primarily deals with different representations of topics or topic patterns to be used in logging, debugging, or user messages.

This file focuses on converting Kafka topic subscription data—either as explicit topic names or as regex patterns—into descriptive strings that clearly indicate whether the subscription is via a topic name or a pattern.

Classes and Methods

Class: TopicHelper

• Type: final utility class

• Accessibility: public

• Purpose: Contains static methods to generate printable string descriptions of Kafka topics or topic patterns.

• Instantiation: Not instantiable (private constructor).

Constructor

private TopicHelper()

• Private constructor to prevent instantiation since this is a utility class.

Method: getPrintableTopic(Pattern topicPattern, Collection<String> topics)

public static String getPrintableTopic(Pattern topicPattern, Collection<String> topics)

• Description: Returns a human-readable string that identifies either a topic pattern or a list of topic names.

• Parameters:

  • Pattern topicPattern: A regex pattern representing Kafka topic subscription. Can be null if explicit topics are used.

  • Collection<String> topics: A collection of Kafka topic names. Used when topicPattern is null.

• Returns: String - a formatted string describing the topic subscription, either "topic pattern " or "topic(s) ".

• Usage example:

Pattern pattern = Pattern.compile("test-topic.*");
Collection<String> topics = Arrays.asList("topic1", "topic2");

String result1 = TopicHelper.getPrintableTopic(pattern, topics);
// result1 = "topic pattern test-topic.*"

String result2 = TopicHelper.getPrintableTopic(null, topics);
// result2 = "topic(s) topic1,topic2"

Method: getPrintableTopic(Pattern topicPattern, String topicName)

public static String getPrintableTopic(Pattern topicPattern, String topicName)

• Description: Similar to the above method but for a single topic name instead of a collection.

• Parameters:

  • Pattern topicPattern: A regex pattern representing Kafka topic subscription. Can be null.

  • String topicName: A single Kafka topic name.

• Returns: String - a descriptive string like "topic pattern " or "topic(s) ".

• Usage example:

Pattern pattern = Pattern.compile("my-topic.*");
String topicName = "my-topic";

String result1 = TopicHelper.getPrintableTopic(pattern, topicName);
// result1 = "topic pattern my-topic.*"

String result2 = TopicHelper.getPrintableTopic(null, topicName);
// result2 = "topic(s) my-topic"

Method: getPrintableTopic(TopicInfo topicInfo)

public static String getPrintableTopic(TopicInfo topicInfo)

• Description: Overloaded convenience method that extracts topic pattern and topic names from a TopicInfo object and formats them.

• Parameters:

  • TopicInfo topicInfo: An object encapsulating Kafka topic subscription details, which provides a pattern and a collection of topics.

• Returns: String - formatted string describing the topic subscription.

• Usage example:

TopicInfo info = ...; // assume properly instantiated with pattern and topics
String result = TopicHelper.getPrintableTopic(info);
// e.g. returns "topic pattern my-topic.*" or "topic(s) topic1,topic2"

Important Implementation Details

• The class is designed as a utility class with all methods declared static and a private constructor to prevent instantiation.

• The logic in each getPrintableTopic method checks if a topic pattern is provided (non-null). If so, it returns a string indicating a pattern subscription; otherwise, it returns a string listing the explicit topic names.

• The class relies on the TopicInfo class (from org.apache.camel.component.kafka.consumer.support.subcription) which holds topic subscription details such as the pattern and the list of topics. This promotes separation of responsibilities.

• Using String.join(",", topics) ensures that multiple topics are concatenated in a comma-separated list without trailing commas or extra spaces.

Interaction with Other Parts of the System

• Kafka Consumer Component: This helper class supports the Kafka consumer component within Apache Camel by providing readable topic representations for logs, error messages, or debugging outputs.

• TopicInfo: The interaction with the TopicInfo class shows that it acts as a data holder for topic subscription information. TopicHelper depends on TopicInfo for a convenient method overload.

• Logging and Monitoring: The printable topic strings generated by this class are likely used in logging or monitoring subsystems to clarify which topics or patterns a consumer is subscribed to.

Diagram: Class Structure of TopicHelper

classDiagram
    class TopicHelper {
        <<utility>>
        -TopicHelper()
        +getPrintableTopic(Pattern, Collection<String>) String
        +getPrintableTopic(Pattern, String) String
        +getPrintableTopic(TopicInfo) String
    }

Summary

The `TopicHelper` class is a straightforward, focused utility class that assists in converting Kafka topic subscription information into human-readable strings. It supports both regex pattern subscriptions and explicit topic name subscriptions, handling both single topic and multiple topic cases. Its simplicity and clear separation from core subscription logic make it a clean utility within the Kafka consumer support subsystem of Apache Camel.