10 Spring Boot Logging Best Practices

Spring Boot is a popular Java web application framework. It is used to create stand-alone, production-grade Spring-based applications. One of the key features of Spring Boot is its embedded Tomcat server.

Tomcat is a lightweight Java web server and servlet container. Spring Boot uses Tomcat by default. Spring Boot also provides a number of features to configure and manage Tomcat.

In this article, we will discuss 10 Spring Boot logging best practices. We will also look at how to configure logging in Spring Boot.

1. Use the Spring Boot Starter

The Spring Boot Starter is a great way to get started with logging in Spring Boot. It provides an opinionated configuration that sets up the most common logging patterns (such as logback) and provides some sensible defaults.

If you’re just getting started with Spring Boot logging, the Spring Boot Starter is a great way to go. You can always customize the logging configuration later if you need to.

2. Log to a File

When you log to a file, you can:

– Centralize all your logs in one place
– Archive your logs for long-term storage
– Monitor your logs for errors and warnings in real-time
– Analyze your logs for trends and insights

Logging to a file is the most efficient way to manage your Spring Boot logs, and it’s also the easiest way to get started with logging. All you need to do is add a few lines of configuration to your application.properties file, and you’re good to go.

3. Configure logging levels

If you don’t configure logging levels, then by default, Spring Boot will only log messages with a level of INFO or higher. This means that any DEBUG or TRACE messages will not be logged.

While this might be fine for some applications, in most cases, it’s not ideal. For example, if you’re trying to debug a problem, then having DEBUG-level logging enabled can be extremely helpful.

Therefore, it’s generally best to configure logging levels so that all messages are logged. Of course, you can always filter the logs later if needed. But it’s much easier to do that than try to enable DEBUG-level logging after the fact.

There are two ways to configure logging levels in Spring Boot. The first is to use the application.properties file, and the second is to use the Logback configuration file.

4. Send logs to an external system

When you’re running a Spring Boot application in production, it’s important to have visibility into what’s going on with your application. Logs are one of the best ways to get that visibility, but if those logs are only stored locally on the server where your application is running, then you’re limited in how you can access and analyze them.

Sending your logs to an external system (like Splunk, Elasticsearch, or even just a central logging server) gives you more flexibility in how you can access and analyze your logs. It also allows you to offload storage of your logs to another system, so you don’t have to worry about filling up your local disk space.

There are a few different ways to send logs to an external system from Spring Boot, but one of the easiest ways is to use the spring-boot-starter-logging starter. This starter will automatically configure your application to send logs to Logstash, which can then forward them to any other system you want.

5. Turn on debug mode

When debug mode is turned on, Spring Boot will include additional information in the logs that can be very helpful when troubleshooting issues. This information includes the values of variables and properties, as well as the flow of execution through the code.

Debug mode should only be turned on when needed, as the extra information included in the logs can make them quite verbose. When debug mode is no longer needed, it should be turned off to avoid unnecessarily cluttering the logs.

6. Limit log output

If you have too much logging output, it can be difficult to find the information you’re looking for. This is especially true if you’re using a log management tool that aggregates logs from multiple sources.

It’s also important to limit log output because it can impact application performance. Generating and writing log messages takes time, and if you have too many log messages, it can slow down your application.

To limit log output, you can use filters to specify which log messages should be written to the log file. For example, you can filter by log level, so only messages with a certain log level are written to the log file.

You can also use Spring Boot’s LoggingCondition class to dynamically determine whether a log message should be written to the log file. This is useful if you want to change the log level at runtime based on some condition.

Finally, you can configure the size of the log file and how often it should be rotated. This ensures that the log file doesn’t get too large and that old log messages are removed periodically.

7. Don’t use System.out or System.err for logging

System.out and System.err are for printing to the console, not for logging. When you use them for logging, your logs will be intermingled with other output from the application, making it difficult to read and understand.

Instead, use a logging framework like Log4j or Logback. These frameworks provide many features that make logging easier, such as the ability to configure log levels, add appenders to send logs to different destinations, and format log messages.

If you’re using Spring Boot, you can use the spring-boot-starter-logging starter to add a logging framework to your project.

8. Use Mapped Diagnostic Context (MDC)

MDC is a thread-local variable that can be used to store contextual information. This information is then included in every log statement automatically, which makes it very useful for tracking requests as they flow through the system.

For example, you could use MDC to store the user ID of the currently logged-in user. Then, every time a request is made, the user ID would be automatically included in the log statements, making it easy to track which user made which request.

To use MDC in Spring Boot, you first need to add the spring-boot-starter-log4j2 dependency to your project. Then, you can configure MDC by adding the following property to your application.properties file:

logging.pattern.level=%X{userId} %-5p [%t] %c{1}:%L – %m%n

This will cause the user ID to be appended to every log statement at the DEBUG level or higher.

9. Use Aspect Oriented Programming (AOP)

AOP allows you to modularize your logging code so that it’s not intermingled with your business logic. This makes your code more maintainable and easier to read.

AOP also enables you to reuse your logging code across multiple classes. For example, if you have a method that logs the start and end time of a method invocation, you can use AOP to weave that logging code into any number of methods without having to duplicate the code.

Finally, AOP gives you the ability to add new logging behavior without changing your existing code. For example, you could use AOP to add logging around all methods annotated with @Transactional.

10. Use SLF4J Markers

Markers are a powerful mechanism that can be used to enhance log statements. A marker is simply an object that contains a name and can optionally contain other markers. Markers are used to add contextual information to log statements. For example, you could create a marker for a specific user and then add that marker to all log statements generated by that user’s actions.

When using SLF4J Markers, there are two things to keep in mind. First, markers are not serializable, so they should not be added to log messages that will be sent over the network. Second, markers are mutable, so they should not be used as keys in maps or stored in static variables.