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Version: 3.0.x

Plugin Overview

The plugin mechanism is a primary way for BifroMQ to deeply integrate with business systems. Currently, BifroMQ exposes four types of plugin extension interfaces to cater to different usage scenarios:

  • Auth Provider: Integrates authentication and topic Pub/Sub authorization logic.
  • Event Collector: Collects runtime events to implement various event-driven business logic.
  • Resource Throttler: Dynamically controls resource usage at the tenant level.
  • Setting Provider: Dynamically adjusts tenant-specific MQTT protocol settings.

Plugin Development​

  • Project Organization: A pf4j project can contain multiple plugin implementations.
  • Singleton Plugins: Extensions of AuthProvider, Resource Throttler, and Setting Provider types are singletons at runtime. The specific type to be loaded needs to be specified through a configuration file.
  • Multiple Instance Plugins: EventCollector allows for multiple different types of instances to exist, with interface methods of these EventCollector instances being called back simultaneously.

Plugin Deployment​

  • Plugin Directory: BifroMQ loads plugin implementations (JAR files or directories) from the plugins subdirectory within its installation directory.
  • Classloader Isolation: Each plugin uses an independent ClassLoader to isolate its code from BifroMQ and other plugins.
  • BifroMQ provides class loading for the following commonly used packages:
    • com.baidu.bifromq.*
    • io.micrometer.core.*
    • com.google.protobuf.*
    • org.slf4j.*

Note: Some dependencies inside a plugin, such as KafkaProducer, may use Java Reflection during instantiation. This process might use Thread.currentThread().getContextClassLoader() to load target classes, which could lead to a ClassNotFoundException. For such cases, it's necessary to explicitly set the context class loader to the corresponding plugin class loader. For example:

ClassLoader contextLoader = Thread.currentThread().getContextClassLoader();
Thread.currentThread().setContextClassLoader(YOUR_PLUGIN_INSTANCE.getClass().getClassLoader());
try{
        // YOUR CODE TO INITIATE KAFKA PRODUCER;
}
finally{
        Thread.currentThread().setContextClassLoader(contextLoader);
}

Version Compatibility​

To ensure optimal compatibility and avoid potential issues, it is advised to deploy your custom plugin with the main version of the BifroMQ main program aligned.

Example:

  • If BifroMQ's version is 3.x.y, then the version of the plugin interface definition modules used should also be 3.x.y.

Performance Considerations​

BifroMQ calls plugin interface methods on worker threads. Ensure plugin interface implementations are lightweight and non-blocking to avoid negatively impacting performance.