@EnableWebMvc启动springmvc特性

矫情吗；* 2022-02-21 10:31 243阅读 0赞

## 使用 ##

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

WebMvcConfigurerAdapter 实现类，配置跨域，添加静态页面等功能

@Configuration
    public class WebMvcConfig extends WebMvcConfigurerAdapter {
    
        @Autowired
        RedisData redisData;
    
        @Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
    
            registry.addResourceHandler("/**").addResourceLocations("classpath:/static/");
            registry.addResourceHandler("swagger-ui.html")
                .addResourceLocations("classpath:/META-INF/resources/");
            registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/");
        }
    
        @Override
        public void addCorsMappings(CorsRegistry registry) {
            registry.addMapping("/**")
                    .allowedOrigins("*")
                    .allowCredentials(true)
                    .allowedMethods("GET", "POST", "DELETE", "PUT")
                    .maxAge(3600);
        }
    
    }

## 原理 ##

@EnableWebMvc注解注入了DelegatingWebMvcConfiguration的bean

@Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.TYPE})
    @Documented
    @Import({DelegatingWebMvcConfiguration.class})
    public @interface EnableWebMvc {
    }

启动加载所有WebMvcConfigurer实例

@Configuration
    public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
        private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
    
        public DelegatingWebMvcConfiguration() {
        }
    
        @Autowired(
            required = false
        )
        public void setConfigurers(List<WebMvcConfigurer> configurers) {
            if(!CollectionUtils.isEmpty(configurers)) {
                this.configurers.addWebMvcConfigurers(configurers);
            }
    
        }
    ...
    }

WebMvcConfigurerComposite 使用组合模式，是树枝节点

class WebMvcConfigurerComposite implements WebMvcConfigurer {
        private final List<WebMvcConfigurer> delegates = new ArrayList();
    
        WebMvcConfigurerComposite() {
        }
    
        public void addWebMvcConfigurers(List<WebMvcConfigurer> configurers) {
            if(!CollectionUtils.isEmpty(configurers)) {
                this.delegates.addAll(configurers);
            }
    
        }