Mastering SpringBoot Path Variables: Regex, Placeholders, and Suffix Matching

Environment: SpringBoot 3.2.5

1. Regular‑Expression Path Variables

Controller mapping can use {varName:regex} to capture parts of the URL and pass them as method parameters, increasing routing flexibility.

@GetMapping("/{name:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{ext:\\.[a-z]+}")
public Object p1(@PathVariable String name, @PathVariable String version, @PathVariable String ext) {
    return String.format("%s-%s%s", name, version, ext);
}

name matches one or more lowercase letters or hyphens ( [a-z-]+); version matches three numbers separated by dots ( \\d\\.\\d\\.\\d); ext matches a dot followed by one or more lowercase letters ( \\.[a-z]+).

2. URI Placeholder (${...})

URI patterns can embed ${...} placeholders that are resolved at startup using PropertySourcesPlaceholderConfigurer. This allows external configuration of base URLs.

@GetMapping("${pack.uri}")
public Object uri() {
    // TODO
    return "uri";
}

Define the placeholder in application.yml:

pack:
  uri: /xxxooo

Combination with a static prefix:

@GetMapping("/api${pack.uri}")
public Object uri() { }

SpEL expression can also be used:

@GetMapping("/api${pack.uri}/#{1+2}")
public Object uri() { }

3. Class‑Level Path Parameter

@RestController
@RequestMapping("/users/{type}")
public class PathController {
    @GetMapping("/single/{id}")
    public Object p1(@PathVariable Integer type, @PathVariable Long id) {
        return DATAS.stream()
            .filter(u -> type == u.getType() && id == u.getId())
            .collect(Collectors.toList());
    }
}

The {type} variable is defined at the class level and can be accessed directly in method parameters.

4. Suffix Matching and Content Negotiation

Since Spring MVC 5.3, path patterns ending with .* are no longer matched by default, and the path extension is not used to determine the response media type. The feature was deprecated in 5.2.4 and removed in later versions.

For older versions you can enable it via configuration:

spring:
  mvc:
    contentnegotiation:
      favor-path-extension: true

Or programmatically in Spring 6.x:

@Component
public class PathWebMvcConfigurer implements WebMvcConfigurer {
    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
        // Enable path‑extension based negotiation
        configurer.favorPathExtension(true);
    }
}

Example endpoint using suffix pattern:

@GetMapping("/{id}/fmt.*")
public Object p1(@PathVariable Long id) {
    return DATAS.stream()
        .filter(u -> id == u.getId())
        .collect(Collectors.toList());
}

When the request ends with .json, the response is JSON; for .xml you need the Jackson XML module:

<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-xml</artifactId>
</dependency>

After adding the dependency, Spring automatically registers an XML message converter. Custom formats require implementing a custom HttpMessageConverter.