Resolving Swagger Configuration Issues in Spring Boot Applications

Problem: org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException

Method 1

Dependency Configuration:

<dependency>
 <groupId>io.springfox</groupId>
 <artifactId>springfox-swagger2</artifactId>
 <version>2.9.2</version>
</dependency>
<dependency>
 <groupId>io.springfox</groupId>
 <artifactId>springfox-swagger-ui</artifactId>
 <version>2.9.2</version>
</dependency>

In your Swagger configuration class, add the @EnableWebMvc annotation to explicitly enable Spring MVC annotation-driven configuration. This ensures better integration between Swagger and Spring MVC for proper API documentation generation.

Analysis:

• Swagger requires tight integration with Spring MVC to automatically scan and register RESTful interfaces from controllers.
• @EnableWebMvc activates Spring MVC's annotation-driven functionality, which is crucial for Swagger to parse annotations in controllers.
• This annotation overrides Spring Boot's auto-configuration, requiring manual configuration of some settings previously provided by auto-configuration.
• Static resource handling may need additional configuration since @EnableWebMvc affects how static resources are served.

Method 2

Dependency Configuration:

<dependency>
    <groupId>com.github.xiaoymin</groupId>
    <artifactId>knife4j-spring-boot-starter</artifactId>
    <version>2.0.7</version>
</dependency>

Configuration Class:

package com.example.apidoc.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.service.ApiInfo;
import springfox.documentation.service.Contact;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2WebMvc;

@Configuration
@EnableSwagger2WebMvc
public class ApiDocConfig {
    @Bean(value = "apiDocumentation")
    public Docket apiDocumentation() {
        return new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(apiDetails())
                .pathMapping("/")
                .select()
                .apis(RequestHandlerSelectors.basePackage("com.example.controller"))
                .paths(PathSelectors.any())
                .build();
    }

    private ApiInfo apiDetails() {
        return new ApiInfoBuilder()
                .title("API Documentation")
                .contact(new Contact("Tech Team", "www.example.com", "support@example.com"))
                .description("Service API Documentation")
                .termsOfServiceUrl("No terms of service")
                .version("1.0")
                .build();
    }
}

Access URL: localhost:configured-port/api/doc.html

Note: For Spring Boot version >= 2.6.x, add the following configuration:

spring:
    mvc:
        path-match:
            matching-strategy: ANT_PATH_MATCHER