M04 Q07 Can you control logging with Spring Boot? How?

Spring Boot allows you to configure following aspects of logging:

Logging Levels

Logging Levels can be set via application.properties:

logging.level.root=WARN
app.service.a.level=ALL
app.service.b.level=FINEST
app.service.c.level=FINER

or by using logging system specific configuration, logback-spring.xml example:

<logger name="app.service.a" level="INFO"/>
<logger name="app.service.b" level="DEBUG"/>
<logger name="app.service.c" level="WARN"/>

You can also use ––debug or ––trace argument when launching spring boot application:

$ java -jar myapp.jar ––debug

It is also possible to specify debug=true or trace=true in application.properties.

Logging Pattern

Logging patterns can be set via application.properties:

logging.pattern.console=%clr(%d{yy-MM-dd E HH:mm:ss.SSS}) \
{blue} %clr(%-5p) %clr(${PID}){faint} \
%clr(---){faint} %clr([%8.15t]){cyan} \
%clr(%-40.40logger{0}){blue} \
%clr(:){red} %clr(%m){faint}%n

or by using logging system specific configuration, logback-spring.xml example:

<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
  <encoder>
    <pattern>%d{yyyy-MM-dd} | %d{HH:mm:ss.SSS} | %thread | %5p | %logger{25} | %12(ID: %8mdc{id}) | %m%n</pattern>
    <charset>utf8</charset>
  </encoder>
</appender>

Logging Colors

When ANSI support for logging output is enabled, you can use colors to format your logs. Colors are used with %clr word.

Example:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

Example usage in logback-spring.xml:

<appender name="2CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
  <encoder>
    <pattern>%clr(%thread){red} | %5p | %logger{25} | %m%n</pattern>
    <charset>utf8</charset>
  </encoder>
</appender>

Following colors are supported:

• blue
• cyan
• faint
• green
• magenta
• red
• yellow

Logging Output – console, file

Spring Boot by default logs only to console. You can change this behavior via application.properties or by using logging system specific configuration.

If you want to change this behavior via application.properties, you need to set one of following property:

logging.file=
logging.path=

You can also do this via logging system specific configuration, for example logbackspring.xml:

<root level="INFO">
    <appender-ref ref="CONSOLE"/>
    <appender-ref ref="FILE"/>
    <appender-ref ref="ROLLING-APPENDER"/>
</root>

Logging Rotation

Spring Boot allows you to control logs rotation by specifying maximum file size and maximum number of logs file to keep in history.

To achieve this behavior through application.properties, you need to set following properties:

logging.file.max-size=
logging.file.max-history=

You can also configure logging system specific settings, for example in logbackspring.xml you can configure rolling appender:

<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
    <fileNamePattern>
        ${LOG_PATH}/archived/log_%d{dd-MM-yyyy}_%i.log
    </fileNamePattern>
    <maxFileSize>10MB</maxFileSize>
    <maxHistory>10</maxHistory>
    <totalSizeCap>100MB</totalSizeCap>
</rollingPolicy>

Logging Groups

Spring Boot can group loggers into group, which simplifies log management.

You can do this on application.properties level in following way:

logging.group.service-d-and-e=app.service.d, app.service.e
logging.level.service-d-and-e=DEBUG

Logging System used

Spring Boot allows you to chose between logging subsystem

To use default Logback, you just need to use spring-boot-starter dependency, autoconfiguration will setup all required beans:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
  </dependency>
</dependencies>

To use log4j2, you just need to exclude spring-boot-starter-logging and add dependency to log4j2:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-logging</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
  </dependency>
</dependencies>

To use JDK (Java Util Logging), you need to exclude spring-bootstarter-logging:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-logging</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
</dependencies>

Then initialize JDK logging in the code:

LogManager.getLogManager().readConfiguration(
        SpringBootConsoleApplication.class.getResourceAsStream("/logging.properties")
);

Logging System specific configuration

• Logback – logback-spring.xml
• log4j2 - log4j2-spring.xml
• JDK (Java Util Logging) - logging.properties