Getting "TemplateProcessingException: Instantiation of new objects and access to static classes or parameters is forbidden in this context"

[mohamz]

After upgrading to spring-boot 4 we get this error message when we add the path to our contract in the "explore" field.
Could anybody please help with this? It blocking us from upgrading to spring-boot 4...

[LienThuan04]

You didn't paste the actual error message, but this is one of the most common issues after upgrading. Here are the fixes ranked by likelihood:

1. Update springdoc-openapi to Spring Boot 4 compatible version

Update springdoc-openapi to Spring Boot 4 compatible version

<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
    <version>3.0.0</version> <!-- must match Spring Boot 4
</dependency>

Mismatched versions cause the explore field to silently fail or return a CORS/404 error.

---

Spring Security blocking the swagger paths

Spring Boot 4 security auto-config is stricter. Explicitly permit swagger endpoints:

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) t
    http.authorizeHttpRequests(auth -> auth
        .requestMatchers(
            "/swagger-ui/**",
            "/swagger-ui.html",
            "/v3/api-docs/**",
            "/v3/api-docs.yaml"
        ).permitAll()
        .anyRequest().authenticated()
urn http.build();
}

---

3. CORS blocking the explore field fetch

If entering the contract URL triggers a CORS error in the browser console:

@Bean
rn new WebMvcConfigurer() {
        @Override
        public void addCorsMappings(CorsRegistry registry) {
            registry.addMapping("/v3/api-docs/**").allowedOrigins("*");
        }
    };
}

---

Could you paste the actual error message? Either the browse log — that would narrow it down to exactly which of theseis the cause.