Master Spring Boot: Unified Paths, Static Resources, Validation, and More

Environment: SpringBoot 2.7.16

1. Unified Path

To give all controller endpoints a common prefix, configure a WebFluxConfigurer that adds the "/api" prefix to every request.

<code>@Configuration
public class WebConfig implements WebFluxConfigurer {
    @Override
    public void configurePathMatching(PathMatchConfigurer configurer) {
        configurer.addPathPrefix("/api", t -> true);
    }
}</code>

This forces every controller request to start with "/api".

2. Static Resource Registration

Spring Boot by default serves static resources from classpath:/META-INF/resources/ , classpath:/resources/ , classpath:/static/ , and classpath:/public/ . To register a custom location, implement WebMvcConfigurer:

<code>@Component
public class StaticResourceConfig implements WebMvcConfigurer {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        // Local file system path, prefix must be "file:"
        registry.addResourceHandler("/static/**")
                .addResourceLocations("file:D:/images/");
    }
}</code>

3. Parameter Validation

Include spring-boot-starter-validation to use annotation‑based validation with @Validated or @Valid . For custom validation logic, register your own validator:

<code>@RestController
@RequestMapping("/users")
public class UserController {
    @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.addValidators(new UserValidator());
    }
}

// UserValidator implementation
public class UserValidator implements Validator {
    @Override
    public boolean supports(Class<?> clazz) {
        return clazz.isAssignableFrom(User.class);
    }

    @Override
    public void validate(Object target, Errors errors) {
        User user = (User) target;
        if (user.getAge() > 150) {
            errors.reject("age", "年龄不能超过150");
        }
        if (user.getName() == null || user.getName().equals("")) {
            errors.reject("name", "姓名不能为空");
        }
    }
}</code>

4. Exception Handling

Define a global exception handler with @RestControllerAdvice and @ExceptionHandler . You can also extend Spring's ResponseEntityExceptionHandler to customize handling of common exceptions:

<code>@Component
public class CustomResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {
    @Override
    protected ResponseEntity<Object> handleExceptionInternal(Exception ex, Object body, HttpHeaders headers,
                                                             HttpStatus status, WebRequest request) {
        // Implement custom logic
        return new ResponseEntity<>(ex.getMessage(), headers, status);
    }
}</code>

Default exception handling options are shown in the following diagram:

5. Retrieve Full Request Information

Use HttpEntity<T> in a controller method to access both request headers and body:

<code>@RestController
@RequestMapping("/users")
public class UserController {
    @PostMapping("")
    public Object save(HttpEntity<User> entity) {
        // Through HttpEntity you can obtain body and header information.
    }
}</code>

6. Built‑in CORS Filter

Spring Web provides a CORS filter that can be registered as a bean:

<code>@Bean
CorsFilter corsFilter() {
    CorsConfiguration config = new CorsConfiguration();
    config.setAllowCredentials(true);
    config.addAllowedOrigin("http://www.pack.com");
    config.addAllowedHeader("*");
    config.addAllowedMethod("*");

    UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
    source.registerCorsConfiguration("/**", config);
    return new CorsFilter(source);
}</code>

7. Customize Default Error Page

Spring Boot maps /error to a default error page. Implement a custom ErrorController and adjust server.error.path in configuration:

<code>@RestController
@RequestMapping("/error")
public class PackErrorController implements ErrorController {
    @GetMapping("")
    public Object e() {
        return "error...";
    }
}</code>

<code>server:
  error:
    # Ensure the custom ErrorController matches this path
    path: /pack/error</code>

8. Correctly Obtain ServletContext

In an embedded container, ServletContext is not reliably available during bean initialization. Listen for ApplicationStartedEvent to capture it after the server starts:

<code>@Component
public class PackComponent implements ApplicationListener<ApplicationStartedEvent> {
    private ServletContext servletContext;

    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        ApplicationContext applicationContext = event.getApplicationContext();
        this.servletContext = ((WebApplicationContext) applicationContext).getServletContext();
    }
}</code>

The ApplicationStartedEvent is published after the application is essentially ready, before any CommandLineRunner or ApplicationRunner callbacks.

These are all the techniques covered in this article.