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Log with the Azure SDK for Java and Logback

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This article provides an overview of how to add logging using Logback to applications that use the Azure SDK for Java. As mentioned in Configure logging in the Azure SDK for Java, all Azure client libraries log through SLF4J, so you can use logging frameworks such as Logback.

To enable Logback logging, you must do two things:

  1. Include the Logback library as a dependency,
  2. Create a file called logback.xml in the /src/main/resources project directory.

For more information related to configuring Logback, see Logback configuration in the Logback documentation.

Add the Maven dependency

To add the Maven dependency, include the following XML in the project's pom.xml file. Replace the 1.2.3 version number with the latest released version number shown on the Logback Classic Module page.

<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.2.3</version>
</dependency>

Add logback.xml to your project

Logback is one of the popular logging frameworks. To enable Logback logging, create a file called logback.xml in the ./src/main/resources directory of your project. This file contains the logging configurations to customize your logging needs. For more information on configuring logback.xml, see Logback configuration in the Logback documentation.

Console logging

You can create a Logback configuration to log to the console as shown in the following example. This example is configured to log all logging events that are INFO level or higher, wherever they come from.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>
        %black(%d{ISO8601}) %highlight(%-5level) [%blue(%t)] %blue(%logger{100}): %msg%n%throwable
      </Pattern>
    </layout>
  </appender>

  <root level="INFO">
    <appender-ref ref="STDOUT" />
  </root>
</configuration>

Log Azure core errors

The following example configuration is similar to the previous configuration, but it lowers the level at which logging comes from all com.azure.core packaged classes (including subpackages). This way, everything INFO-level and higher is logged, except for com.azure.core, where only ERROR-level and higher is logged. For example, you can use this approach if you find the code in com.azure.core too noisy. This kind of configuration can also go both ways. For example, if you want to get more debug information from classes in com.azure.core, you could change this setting to DEBUG.

It's possible to have fine-grained control over the logging of specific classes, or specific packages. As shown here, com.azure.core controls the output of all core classes, but you could equally use com.azure.security.keyvault or equivalent to control the output as appropriate for the circumstances that are most informative in the context of the running application.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%message%n</pattern>
    </encoder>
  </appender>

  <logger name="com.azure.core" level="ERROR" />

  <root level="INFO">
    <appender-ref ref="STDOUT" />
  </root>
</configuration>

Log to a file with log rotation enabled

The previous examples log to the console, which isn't normally the preferred location for logs. Use the following configuration to log to a file instead, with hourly roll-over, and archiving in gzip format:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <property name="LOGS" value="./logs" />
  <appender name="RollingFile" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${LOGS}/spring-boot-logger.log</file>
    <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
      <Pattern>%d %p %C{1.} [%t] %m%n</Pattern>
    </encoder>

    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
      <!-- rollover hourly and gzip logs -->
      <fileNamePattern>${LOGS}/archived/spring-boot-logger-%d{yyyy-MM-dd-HH}.log.gz</fileNamePattern>
    </rollingPolicy>
  </appender>

  <!-- LOG everything at INFO level -->
  <root level="INFO">
    <appender-ref ref="RollingFile" />
  </root>
</configuration>

Spring applications

The Spring framework works by reading the Spring application.properties file for various configurations, including the logging configuration. It's possible to configure the Spring application to read Logback configurations from any file, however. To do so, configure the logging.config property to point to the logback.xml configuration file by adding the following line into your Spring /src/main/resources/application.properties file:

logging.config=classpath:logback.xml

Next steps

This article covered the configuration of Logback and how to make the Azure SDK for Java use it for logging. Because the Azure SDK for Java works with all SLF4J logging frameworks, consider reviewing the SLF4J user manual for further details. If you use Logback, there's also a vast amount of configuration guidance on its website. For more information, see Logback configuration in the Logback documentation.

After you've mastered logging, consider looking into the integrations that Azure offers into frameworks such as Spring and MicroProfile.