springboot-best-practices

This tutorial is derived from: Spring Boot Best Practices For Developers 👨‍💻 (Youtube/JavaTechie) and Spring Boot Best Practices for Developers (Medium/RaviYasas)

This is a guide for best practices and includes tips which you can use to improve your Spring Boot application and make it more efficient.

Table of Contents

Getting Started
0. Notable Mentions
1. Proper packaging style
2. Use Spring Boot starters
3. Use proper versions of the dependencies
4. Use Lombok
5. Use Controllers only for routing
6. Use Services for business logic
7. Use constructor injection with Lombok
8. Use Slf4j logging
9. Use meaningful words for classes, methods, variables and other attributes
10. Bean Validation
11. Custom Exception Handling
12. Use custom response object
13. Use design patterns
14. Use yml instead of properties
15. Encrypt or externalize sensitive info
16. Write E2E Unit Test cases with coverage
17. Avoid NPE by using Optional
18. Use best practices for the collection framework
19. Use Caching
20. Use Pagination
21. Remove unnecessary codes, variables, methods
22. Use Comments
23. Use a common code formatting style
24. Use SonarLint
25. Be Simple!

Getting Started

Prerequisites

Git
Java 8
Maven

Running the App

Open your terminal or command prompt.

Clone the repository using Git:

git clone https://github.com/arsy786/springboot-best-practices.git

Navigate to the cloned repository's root directory:
```
cd springboot-best-practices
```

Run the following Maven command to build and start the service:

# For Maven
mvn spring-boot:run

# For Maven Wrapper (automatically uses the correct Maven version)
./mvnw spring-boot:run

The application should now be running on localhost:9191.

Database Configuration

Configure your MySQL database connection by editing the application.yml in src/main/resources:

#DataSource Configuration
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/javatechie
    username: root
    password: root

Replace the url with your database's JDBC URL.
Update username and password as needed.

NOTE: To use a different SQL database, include the appropriate database driver in your pom.xml and update the application.yml config accordingly.

0. Notable Mentions

Create application.yml for each environment. For example: application-dev.yml, application-prod.yml ...
Use a library to map DTOs, such as MapStruct.
Use soft delete.
Use environment variables to avoid hard-coding.

1. Proper packaging style

You can structure your application with meaningful packaging.
Proper packaging will help to understand the code and the flow of the application easily.
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 which to adopt, depending on your requirements.

Based on type:

Based on feature:

2. Use Spring Boot starters

We can very easily use starter dependencies without adding single dependencies one by one. These starter dependencies are already bundled with the required dependencies.
Can add these easily using Spring Initializr.
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.
As a result, we don’t need to care about adding dependencies separately.
Also, it helps us to avoid version mismatches.

3. Use proper versions of the dependencies

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

Spring boot starters will have their versions defined by the Parent version, and this will automatically configure all the external libraries to be operating on the same versions! For example:

4. Use Lombok

Lombok is a Java library that is used to reduce boilerplate code and allow you to write clean code using its annotations.
For 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.

5. 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.

For code implementation example(s) check: ProductController.java or TeamController.java

6. 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.

For code implementation example(s) check: ProductService.java or TeamService.java

7. 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.

For code implementation example(s) check: ProductController.java or ProductService.java

8. 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.
You can use Lombok @Slf4j annotation to create a logger very easily.
If you are in a micro-services environment, you can use the ELK stack.

For code implementation example(s) check: ProductController.java and ProductService.java or TeamController.java and TeamService.java and ApiExceptionHandler.java

9. Use meaningful words for classes, methods, variables and other attributes

Always use proper meaningful and searchable naming conventions with proper case.
Usually, we use nouns or short phrases when declaring classes, variables, and constants. For example: String firstName, const isValid
You can use verbs and short phrases with adjectives for functions and methods. For example: readFile(), sendData()
Avoid using abbreviating variable names and intention revealing names. For example: 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.

There are many different case styles we can adopt, as shown above.
But, we must identify which case is dedicated to which variable and be consistent with it. Most common standard:

Classes = PascalCase
Methods & Variables = camelCase
Constants = SCREAMING_SNAKE_CASE
DB-related fields = snake_case

10. Bean Validation

Apply to DTOs.
Use annotations such as @NotBlank, @Min, @Max, and add messages to each.
Use @Valid in Controller POST request method attributes to validate against the DTO bean validation annotations.

NOTE: Use the annotations from javax.persistence._ for adding constraints in the Model/Entity layer.
NOTE: Use the annotations from javax.validation.constraints._ for adding validation in the DTO layer.

For code implementation example(s) check: Team.java and TeamDTO.java or ProductRequestDTO.java

11. Custom Exception Handling

This is very important when working with large enterprise-level applications.
Apart from the general exceptions, we may have some scenarios to 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.

For code implementation example(s) check: FCMS Exception Folder or This Exception Folder with This Handler Folder or Different Project Exception Folder

12. 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.

For code implementation example(s) check: APIResponse.java

13. Use design patterns

Know when and where to use which pattern.
Builder and Singleton most used in Spring Boot applications.

Supporting Material

Using Lombok’s @Builder Annotation (Baeldung/EricGoebelbecker)
Design Patterns in the Spring Framework (Baeldung/JustinAlbano)

14. Use yml instead of properties

Less repetition/duplication of the key prefix.
More readable.
Also, use comments in config file to separate which settings belong to which feature.

For code implementation example(s) check: application.yml

15. Encrypt or externalize sensitive info

Encrypt ALL passwords (never store as plain text).
Move this information outside the codebase (Vault, git server, cloud config, etc.)

Supporting Material

Bcrypt Password Encryption with Spring Boot (Youtube/ProgrammingWithBasar)

16. Write E2E Unit Test cases with coverage

This is done to validate that all features and API's are working as expected.
Why do we mock Repository/Service? We do not want the test data to save to the DB, so mocking the behaviour of methods helps us bypass DB interactions.
Test ALL endpoints/methods.
Test positive AND negative scenarios for each endpoint. Include Edge Cases!
Running the code with Coverage allows us to identify which parts of the code have or have not been tested.
Aim for 100% coverage!

For code implementation example(s) check: All FCMS Tests or TeamMockMvcIT.java or ProductServiceApplicationTests.java

17. Avoid NPE by using Optional

In Java 8, to avoid NullPointerException you can use Optional from java.util.package.
Can use:

Optional.ofNullable(object);

// or

productRepository.findById(productId).orElseThrow(
() -> new ProductNotFoundException("product not found with id: " + productId))

18. Use best practices for the collection framework

Use appropriate collection (data structure) for your data set.
Use forEach with Java 8 features and avoid using legacy for loops.
pre- and post-Java 8 comparison:

// pre-Java 8
Map<String, List<ProductResponseDTO>> productsMap = new HashMap<>();
        List<String> productTypes = Arrays.asList("Electronics", "fashion", "Kitchen");//1st iteration from DB

        List<Product> productList = productRepository.findAll(); //2nd

        for (String type : productTypes) {
            List<ProductResponseDTO> productResponseDTOList = new ArrayList<>();
            for (Product product : productList) {
                if (type.equals(product.getProductType())) {
                    productResponseDTOList.add(ValueMapper.convertToDTO(product));
                }
                productsMap.put(type, productResponseDTOList);
            }
        }

        return productsMap;

// post-Java 8
Map<String, List<ProductResponseDTO>> productsMap = productRepository.findAll().stream()
                            .map(ValueMapper::convertToDTO)
                            .filter(productResponseDTO -> productResponseDTO.getProductType() != null)
                            .collect(Collectors.groupingBy(ProductResponseDTO::getProductType));
return productsMap;

Functional programming is better for performance and readability.
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.

19. Use Caching

Caching is another important factor when talking about application performance.
It reduces the round trip of your request from your application to the DB (if no changes were detected).
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.

Supporting Material

Spring Data Redis as Cache (Youtube/JavaTechie)
Spring Boot Caching With Real Life Example (Youtube/GreenLearner)

20. Use Pagination

This is useful if you have lots of records, it allows us to view the data more easily.
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.

Supporting Material

Pagination and Sorting With Spring Data JPA (Youtube/JavaTechie)
Spring Data JPA Pagination (Youtube/DanVega)

21. Remove unnecessary codes, variables, methods

Unused variable declarations will acquire some memory.
Remove unused methods, classes, imports, vars etc. because it will impact the performance of the application.
Try to avoid nested loops. You can use Java 8 Streams instead.

Supporting Material

Functional Programming with Java Streams API (Youtube/Amigoscode)

22. Use 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.
Example of comment explaining a method:

/** this method will fetch product from DB by ID
* @param productId
* @return product response from DB
*/

23. Use a common code formatting style

Have a consistent and uniform way of formatting your code.
Use spaces and/or returns in an ordered and readable manner.
CMD+OPTION+L on highlighted code in IDE for code reformatting!
Can see below, two different ways of formatting the same code. To avoid discrepancies, you or your team should have a common coding format.

24. 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.

25. Be Simple!

Always try to write readable, understandable and simple code!

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