Spring Boot Best Practices for Developers

Spring Boot is a widely used and very popular enterprise-level high-performance framework. Here are some best practices and some tips you can use to improve your Spring Boot application and make it more efficient. This article will be a little longer, and it will take some time to completely read the article.

Proper packaging style

• Proper packaging will help to understand the code and the flow of the application easily. 
• You can structure your application with meaningful packaging.
• You can include all your controllers into a separate package, services in a separate package, util classes into a separate package…etc. This style is very convenient in small-size microservices.
• If you are working on a huge code base, a feature-based approach can be used. You can decide on your requirement.

Based on type

Based on feature

Use design patterns

• No complaints. Design patterns are already best practices. 
• But you must identify the place where you can use them. 
• Please check this article to understand “how to use the Builder design pattern” in our Spring Boot applications.

Use Spring Boot starters

Image: https://www.merriam-webster.com/words-at-play/names-of-appetizers

• This is a cool feature of Spring Boot.
• We can very easily use starter dependencies without adding single dependencies one by one. These starter dependencies are already bundled with the required dependencies.
• For example, if we add spring-boot-starter-web dependency, by default it is bundled with jackson, spring-core, spring-mvc, and spring-boot-starter-tomcat dependencies.
• So we don’t need to care about adding dependencies separately.
• And also it helps us to avoid version mismatches. 

Use proper versions of the dependencies

• It is always recommended to use the latest stable GA versions.
• Sometimes it may vary with the Java version, server versions, the type of the application…etc.
• Do not use different versions for the same package and always use <properties> to specify the version if there are multiple dependencies.

Use Lombok

• As a Java developer, you have probably heard of the Lombok project.
• Lombok is a Java library that can be used to reduce your codes and allowing you to write clean code using its annotations.
• For an example, you may use plenty of lines for getters and setters in some classes like entities, request/response objects, dtos…etc. 
• But if you use Lombok, it is just one line, you can use @Data, @Getter or @Setter as per your requirement. 
• You can use Lombok logger annotations as well. @Slf4j is recommended.
• Check this file for your reference. 

Use constructor injection with Lombok

• When we talk about dependency injection, there are two types.
• One is “constructor injection” and the other is “setter injection”. Apart from that, you can also use “field injection” using the very popular @Autowired annotation.
• But we highly recommend using Constructor injection over other types. Because it allows the application to initialize all required dependencies at the initialization time. 
• This is very useful for unit testing. 
• The important thing is, that we can use the @RequiredArgsConstructor annotation by Lombok to use constructor injection.
• Check this sample controller for your reference. 

Use slf4j logging

• Logging is very important. 
• If a problem occurs while your application is in production, logging is the only way to find out the root cause.
• Therefore, you should think carefully before adding loggers, log message types, logger levels, and logger messages.
• Do not use System.out.print()
• Slf4j is recommended to use along with logback which is the default logging framework in Spring Boot. 
• Always use slf4j { } and avoid using String interpolation in logger messages. Because string interpolation consumes more memory.
• Please check this file for your reference to get an idea about, implementing a logger. 
• If you are in a micro-services environment, you can use the ELK stack.

Use Controllers only for routing

• Controllers are dedicated to routing.
• It is stateless and singleton.
• The DispatcherServlet will check the @RequestMapping on Controllers
• Controllers are the ultimate target of requests, then requests will be handed over to the service layer and processed by the service layer.
• The business logic should not be in the controllers.

Use Services for business logic

• The complete business logic goes here with validations, caching…etc.
• Services communicate with the persistence layer and receive the results.
• Services are also singleton.

Avoid NullPointerException

• To avoid NullPointerException you can use Optional from java.util package.
• You can also use null-safe libraries. Ex: Apache Commons StringUtils
• Call equals() and equalsIgnoreCase() methods on known objects.
• Use valueOf() over toString()
• Use IDE based @NotNull and @Nullable annotations

Use best practices for the Collection framework

• Use appropriate collection for your data set.
• Use forEach with Java 8 features and avoid using legacy for loops.
• Use interface type instead of the implementation. 
• Use isEmpty() over size() for better readability. 
• Do not return null values, you can return an empty collection.
• If you are using objects as data to be stored in a hash-based collection, you should override equals() and hashCode() methods. Please check this article “How does a HashMap internally work”. 

Use pagination

• This will improve the performance of the application. 
• If you’re using Spring Data JPA, the PagingAndSortingRepository makes using pagination very easy and with little effort.

Use caching

• Caching is another important factor when talking about application performance.
• By default Spring Boot provides caching with ConcurrentHashMap and you can achieve this by @EnableCaching annotation. 
• If you are not satisfied with default caching, you can use Redis, Hazelcast or any other distributed caching implementations.
• Redis and Hazelcast are in-memory caching methods. You also can use database cache implementations as well.

Use custom exception handler with global exception handling

• This is very important when working with large enterprise-level applications.
• Apart from the general exceptions, we may have some scenarios and identify some specific error cases. 
• Exception adviser can be created with @ControllerAdvice and we can create separate exceptions with meaningful details.
• It will make it much easier to identify and debug errors in the future.
• Please check this and this for your reference.

Use custom response object

• A custom response object can be used to return an object with some specific data with the requirements like HTTP status code, API code, message…etc.
• We can use the builder design pattern to create a custom response object with custom attributes.
• Please check this article for your reference. 

Remove unnecessary codes, variables, methods and classes.

commented code in the production

• Unused variable declarations will acquire some memory.
• And also we better remove commented codes and unused methods, classes…etc because it will impact the performance of the application. 
• Try to avoid nested loops. You can use maps instead.

Using comments

• Commenting is a good practice unless you abuse it.
• DO NOT comment on everything. Instead, you can write descriptive code using meaningful words for classes, functions, methods, variables…etc.
• Remove commented codes, misleading comments, and story-type comments.
• You can use comments for warnings and explain something difficult to understand at first sight.

Use meaningful words for class names, methods, variables, and other attributes.

• This looks very simple, but the impact is huge.
• Always use proper meaningful and searchable naming conventions with the appropriate case.
• Usually, we use nouns or short phrases when declaring classes, variables, and constants. Ex: String firstName, const isValid
• You can use verbs and short phrases with adjectives for functions and methods. Ex: readFile(), sendData()
• Avoid using abbreviating variable names and intention-revealing names. Ex: int i; String getExUsr;
• If you use this meaningfully, declaration comment lines can be reduced. Since it has meaningful names, a fresh developer can easily understand by reading the code.

Use proper case for declarations

• There are many different cases like UPPERCASE, lowercase, camelCase, PascalCase, snake_case, SCREAMING_SNAKE_CASE, kebab-case…etc.
• But we need to identify which case is dedicated to which variable.
• Usually, I follow classes — PascalCase, methods — camelCase, conststants — SCREAMING_SNAKE_CASE and fields — snake_case

Be simple

• Always try to write simple, readable codes.
• The same simple logic can be implemented using different ways, but it is difficult to understand if it is not readable or understandable.
• Sometimes complex logic consumes more memory.
• Try to use KISS, DRY, and SOLID principles when writing codes. I will explain this in a future article.

Use a common code formatting style

• Formatting styles vary from developer to developer. Code style is also considered a change and can make code merging very difficult.
• To avoid this, the team can have a common coding format.

Use SonarLint

• This is very useful for identifying small bugs and best practices to avoid unnecessary bugs and code quality issues.
• You can install the plugin into your favorite IDE. 

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This is not the end. There are a lot of small tips and practices. Let’s look at them in the next articles. You can view the same article on my Medium profile.