Spring Boot Framework FAQ

Spring Boot Framework FAQ with practical examples

Spring Boot is a popular framework that allows developers to quickly and easily Create Spring-based applications. Although it is simple and easy to use, users may encounter some common problems while using it.

1. NoClassDefFoundErrorError occurs when starting the application

Problem:
When developing using IDE such as Eclipse , after adding Spring Boot dependency, NoClassDefFoundError error occurred when starting the application.

Solution:
Ensure that the IDE build path is configured to include all required JAR files. In Eclipse, right-click on the project, select Build Path -> Configure Build Path, and go to the Libraries tab. Make sure all Spring Boot dependencies are listed, otherwise add them manually.

2. @SpringBootApplication does not exist under the annotation main method

Problem:
The @SpringBootApplication class with the main method does not exist in the application.

Solution:
Create a new class, add the @SpringBootApplication annotation and implement the main method. Make sure the main method is a public static method of the class, with String[] args arguments.

3. The injected bean is empty

Problem:
The injected bean is empty at runtime.

Solution:
Ensure that the bean is correctly defined and marked as a Spring component. Use annotations like @Component, @Service or @Repository. In addition, check that component scanning is configured correctly and ensure that the package where the autowired bean is located is included in the scan path.

4. The application context loads slowly

Problem:
The application loads slowly at startup.

Solution:
This problem can be solved by optimizing the application configuration. Here are some tips:

• Enable lazy loading: Annotate lazy loading beans with @Lazy.
• Disable unnecessary filters or interceptors.
• Reduce the database connection pool size.

5. Spring Boot Actuator endpoint is not available

Problem:
When the application starts, Spring Boot Actuator endpoint (such as /info) is not available.

Solution:
Make sure you have added the spring-boot-starter-actuator dependency to pom.xml. Additionally, check if the Actuator endpoint is enabled, this can be achieved by setting the management.endpoints.web.exposure.include property in application.yml.

Practical Case

The following is a code snippet that uses Spring Boot to build a simple REST API:

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

@RestController
@RequestMapping("/api")
public class ApiController {
  @GetMapping("/greeting")
  public String greeting() {
    return "Hello World!";
  }
}

In this example, @ The SpringBootApplication annotation creates a Spring Boot application. ApiController is the controller class of REST API, providing a GET endpoint to return a simple greeting.

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