Logging for Kotlin SDK

This page explains how to configure logging in the PubNub Kotlin Software Development Kit (SDK) using SLF4J and custom loggers.

Logging architecture

You can configure logging for different environments and use cases:

• SLF4J integration: All logs route through SLF4J, allowing you to use any SLF4J-compatible backend (logback, log4j, slf4j-simple, commons-logging, java.util.logging)
• Custom loggers: Optionally add custom logger implementations via the customLoggers configuration parameter to route logs to external systems
• Structured logging: Logs include structured data with instance IDs, timestamps, log levels, and typed content

The SDK sends all log entries to both SLF4J and any configured custom loggers simultaneously.

Log levels

SLF4J uses standard log levels:

Level	Purpose
TRACE	Internal operations: serialization, encryption, subscription lifecycle, and detailed execution flow
DEBUG	User inputs, API parameters, HTTP requests and responses, and configuration properties
INFO	Significant events like successful initialization and configuration changes
WARN	Deprecation warnings, unusual conditions, and non-breaking validation warnings
ERROR	Errors, exceptions with stack traces, and failed operations

The SDK logs all configuration properties at DEBUG level during initialization. Sensitive values such as secret keys are masked.

Custom loggers

Beyond SLF4J, you can implement the CustomLogger interface to route logs to external monitoring services, databases, or analytics platforms alongside your SLF4J backend.

CustomLogger interface

The CustomLogger interface supports string messages and structured LogMessage objects:

1interface CustomLogger {
2    val name: String get() = "CustomLogger"
3    
4    // String-based logging methods
5    fun trace(message: String?)
6    fun debug(message: String?)
7    fun info(message: String?)
8    fun warn(message: String?)
9    fun error(message: String?)
10    
11    // Structured logging methods
12    fun trace(logMessage: LogMessage)
13    fun debug(logMessage: LogMessage)
14    fun info(logMessage: LogMessage)
15    fun warn(logMessage: LogMessage)
16    fun error(logMessage: LogMessage)
17}

show all 17 lines

The SDK calls both overloads for each log entry:

• String version - a simplified, human-readable message
• LogMessage version - structured data including instance ID, timestamp, location, and typed content

You only need to implement the methods you plan to use. The default implementations do nothing.

Structured logging with LogMessage

LogMessage provides structured information for each log entry:

Field	Description
message	The log content (one of: Text, Object, Error, NetworkRequest, or NetworkResponse)
details	Optional additional context
type	Automatically inferred from message content (TEXT, OBJECT, ERROR, NETWORK_REQUEST, NETWORK_RESPONSE)
location	Source class or method generating the log
pubNubId	PubNub instance identifier
logLevel	The SLF4J log level (TRACE, DEBUG, INFO, WARN, ERROR)
timestamp	When the log was created with millisecond precision (format: HH:mm:ss.SSS)

Custom logger example

1

Configure the SDK with your custom logger:

1

SLF4J backend configuration

The following sections explain how to configure different SLF4J backends. Choose the backend that best fits your environment and logging requirements.

For more information about configuration parameters, refer to Configuration.

Implement logging on Android

Add the following dependency to the project and configure it.

• Logback Android dependency

Example configuration:

1

The logs will appear in Logcat.

Implement logging using log4j

To implement logging using log4j you need to add the following references to the project. Using log4j you can log to console or a file or both.

• log4j-slf4j2 file which acts as a bridge between slf4j and log4j.
• log4j-api file, which provides the underlying logging framework API.
• log4j-core file, which provides the underlying logging framework Implementation.

1

See this example:

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Implement logging using slf4j-simple

To implement logging using slf4j-simple you need to add the following references to the project.

• SLF4J API dependency
• SLF4J-Simple dependency which provides the underlying logging framework

Along with these references you need to add the simplelogger.properties file in the CLASSPATH.

See this example:

1

Example usage of slf4j-simple

1

Implement logging using logback-classic

To implement logging using logback, you need to add the following references to the project.

• Logback classic and logback-core jar files which provide the underlying logging framework
• Logback core dependency which provides the underlying logging framework

See an sample logback.xml logback config file:

1

See this example:

1

Implement logging using java.util.logging

To implement logging using java.util.logging you need to add the following references to the project.

• SLF4J API dependency
• SLF4J-JDK14 dependency which acts as a bridge between slf4j and java

JVM runtime provides the underlying logging framework.

Implement logging using commons-logging

To implement logging using commons-logging you need to add the following references to the project.

• SLF4J API dependency
• SLF4J-JCL dependency which acts as a bridge between slf4j and common-logging
• commons-logging dependency which acts as an abstraction layer

The underlying logging framework is chosen dynamically by commons-logging.

No logging

To implement no logging you have two options:

• Add the SLF4J API dependency which is the SLF4J API and nothing else.

• Add the SLF4J API dependency and then add a reference to SLF4J-nop dependency.