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Catalog / Spring Boot Cheat Sheet

Spring Boot Cheat Sheet

A quick reference guide to Spring Boot, covering essential annotations, properties, and best practices for rapid application development.

Core Annotations

Application Setup

@SpringBootApplication: A convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan. Marks the main class of a Spring Boot application.

Example:

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

Component Management

@Component

Marks a class as a Spring-managed component. Generic stereotype for any Spring-managed component.

@Service

Specialization of @Component for classes that hold business logic.

@Repository

Specialization of @Component for classes that provide data access (e.g., interacting with databases).

@Controller

Marks a class as a controller, handling incoming web requests.

@RestController

Combination of @Controller and @ResponseBody, indicating that the method’s return value should be bound to the web response body.

Dependency Injection

@Autowired

Injects dependencies into a class. Can be used on fields, constructors, or setter methods.

Example:

@Autowired
private MyService myService;

@Qualifier

Used with @Autowired to specify which bean to inject when there are multiple candidates.

Example:

@Autowired
@Qualifier("myServiceImpl")
private MyService myService;

@Value

Injects values from properties files or environment variables.

Example:

@Value("${my.property}")
private String myProperty;

Web Development

Request Mapping

@RequestMapping

Maps web requests onto controller methods. Supports various attributes like path, method, params, headers, consumes, and produces.

Example:

@RequestMapping(value = "/users", method = RequestMethod.GET)
public List<User> getUsers() { ... }

@GetMapping

Shortcut for @RequestMapping(method = RequestMethod.GET).

Example:

@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) { ... }

@PostMapping

Shortcut for @RequestMapping(method = RequestMethod.POST).

Example:

@PostMapping("/users")
public User createUser(@RequestBody User user) { ... }

@PutMapping

Shortcut for @RequestMapping(method = RequestMethod.PUT).

@DeleteMapping

Shortcut for @RequestMapping(method = RequestMethod.DELETE).

@PatchMapping

Shortcut for @RequestMapping(method = RequestMethod.PATCH).

Request Parameters

@PathVariable

Extracts values from the URI path.

Example:

@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) { ... }

@RequestParam

Extracts values from query parameters.

Example:

@GetMapping("/users")
public List<User> getUsers(@RequestParam(defaultValue = "10") int limit) { ... }

@RequestBody

Binds the request body to a method parameter. Often used to receive JSON or XML data.

Example:

@PostMapping("/users")
public User createUser(@RequestBody User user) { ... }

Response Handling

@ResponseBody

Indicates that a method’s return value should be bound to the web response body. Typically used in @RestController classes.

ResponseEntity<>

Allows fine-grained control over the response, including status code, headers, and body.

Example:

@GetMapping("/users/{id}")
public ResponseEntity<User> getUser(@PathVariable Long id) { ... }

@ResponseStatus

Sets the HTTP status code of the response.

Example:

@ResponseStatus(HttpStatus.CREATED)
@PostMapping("/users")
public User createUser(@RequestBody User user) { ... }

Data Management

JPA Repositories

@Entity: Marks a class as a JPA entity, representing a table in the database.

@Id: Specifies the primary key of an entity.

@GeneratedValue: Configures the strategy for generating primary key values (e.g., IDENTITY, SEQUENCE, AUTO).

JpaRepository<T, ID>: Provides basic CRUD operations and pagination for JPA entities. Extend this interface to create a repository for your entity.

Example:

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByLastName(String lastName);
}

Data Source Configuration

Spring Boot automatically configures a data source if you provide the necessary properties in application.properties or application.yml.

Example properties:

spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=user
spring.datasource.password=password
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

Transactions

@Transactional

Marks a method or class as transactional. Ensures that database operations are executed within a transaction. Supports various attributes like propagation, isolation, timeout, and readOnly.

Example:

@Transactional
public void transferFunds(Long fromAccountId, Long toAccountId, BigDecimal amount) { ... }

Advanced Features

Profiles

Spring Profiles allow you to configure different parts of your application for different environments (e.g., development, testing, production).

@Profile: Marks a component as being active only when a specific profile is active.

Example:

@Component
@Profile("dev")
public class DevDatabaseConfig { ... }

Activate profiles using the spring.profiles.active property in application.properties or application.yml.

Actuator

Spring Boot Actuator provides endpoints for monitoring and managing your application, such as health checks, metrics, and audit events.

Common endpoints include /health, /metrics, /info, /beans, and /env. These can be accessed over HTTP or JMX.

Enable Actuator by adding the spring-boot-starter-actuator dependency to your project.

Testing

@SpringBootTest

Loads the full application context for integration tests.

@WebMvcTest

Tests only the web layer, loading only the necessary components (e.g., controllers, filters, interceptors).

@DataJpaTest

Tests only the JPA components, setting up an in-memory database.

@MockBean

Mocks a bean in the application context, allowing you to isolate the component being tested.
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