Springboot2.x+swagger2突然404解決分析

問題背景

​ 項目正常更新以後，突然swagger-ui.html界面就404了，很奇怪，報錯如下：

GET "/swagger-ui.html", parameters={}
2020-04-24 09:53:38.324 [http-nio-7799-exec-1] [WARN] - No mapping for GET /swagger-ui.html
2020-04-24 09:53:38.325 [http-nio-7799-exec-1] [DEBUG] - Completed 404 NOT_FOUND

​ No mapping for GET /swagger-ui.html這明顯是對應的處理handle-mapping沒有找到啊,奇怪了，之前運行的好好的，項目更新後，就404了呢

代碼比對

​ 於是，Compare搞起，比對發現如下：

@Configuration
public class WebConfig implements WebMvcConfigurer{
    ...
}

​ 修改後：

@Configuration
public class WebConfig extends WebMvcConfigurationSupport{
    ...
}

​ 然後想起來了，同事說，不推薦直接使用WebMvcConfigurer，所以改爲WebMvcConfigurationSupport，但是這也不該影響使用swagger2啊，好奇怪，那麼繼續分析爲啥呢？

分析WebMvcConfigurer

​ 分析WebMvcConfigurer#addResourceHandlers，這裏是註冊handler-mapping映射關係的

//WebMvcConfigurerComposite#addResourceHandlers
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    for (WebMvcConfigurer delegate : this.delegates) {
        delegate.addResourceHandlers(registry);
    }
}

​ 說明有多個WebMvcConfigurer的實現類註冊了，具體如下：

​ 調試，查看，ResourceHandlerRegistry裏面到底處理了那些url path

• /webjars/**
• /**
  
  ​ 查看對應的日誌，果然

Creating chain [/v2/api-docs] from String definition [anon]
2020-04-24 10:07:58.044 [main] [DEBUG] - Attempting to apply path [/v2/api-docs] to filter [anon] with config [null]
# /webjars/springfox-swagger-ui/**
2020-04-24 10:07:58.044 [main] [DEBUG] - Creating chain [/webjars/springfox-swagger-ui/**] from String definition [anon]
2020-04-24 10:07:58.044 [main] [DEBUG] - Attempting to apply path [/webjars/springfox-swagger-ui/**] to filter [anon] with config [null]

​ 所以使用WebMvcConfigurer，swagger2對應的handler被註冊了

分析WebMvcConfigurationSupport

​ 下面分析WebMvcConfigurationSupport#addResourceHandlers，實現如下：

//DelegatingWebMvcConfiguration#addResourceHandlers
protected void addResourceHandlers(ResourceHandlerRegistry registry) {
    // 注意configurers------->WebMvcConfigurerComposite
    this.configurers.addResourceHandlers(registry);
}

​ 也就是說，使用WebMvcConfigurationSupport，最終也是調用到了WebMvcConfigurerComposite#addResourceHandlers,但是在最後的ResourceHandlerRegistry裏面確實沒有/webjars/**，說明，根本就沒有去註冊對應的url。

​ 所以打斷點分析

//WebMvcConfigurerComposite#addResourceHandlers
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    //打斷點
    for (WebMvcConfigurer delegate : this.delegates) {
        delegate.addResourceHandlers(registry);
    }
}

​ 結果，根本就沒有執行到這個方法，也就是使用WebMvcConfigurationSupport根本就沒有去註冊。

​ 怎麼呢？繼續分析WebMvcConfigurer的實現類，因爲是直接使用的starter

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

​ 所以，分析一下WebMvcAutoConfigurationAdapter,

@Configuration
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter
    implements WebMvcConfigurer, ResourceLoaderAware {

    ......
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        if (!this.resourceProperties.isAddMappings()) {
            logger.debug("Default resource handling disabled");
            return;
        }
        Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
        CacheControl cacheControl = this.resourceProperties.getCache()
            .getCachecontrol().toHttpCacheControl();
        // /webjars/** 沒有的話，註冊一下
        if (!registry.hasMappingForPattern("/webjars/**")) {
            customizeResourceHandlerRegistration(
                registry.addResourceHandler("/webjars/**")
                         .addResourceLocations("classpath:/META-INF/resources/webjars/")
                         .setCachePeriod(getSeconds(cachePeriod))
                         .setCacheControl(cacheControl));
        }
        String staticPathPattern = this.mvcProperties.getStaticPathPattern();
        // 靜態資源處理
        if (!registry.hasMappingForPattern(staticPathPattern)) {
            customizeResourceHandlerRegistration(
                registry.addResourceHandler(staticPathPattern)
                .addResourceLocations(getResourceLocations(
                    this.resourceProperties.getStaticLocations()))
                .setCachePeriod(getSeconds(cachePeriod))
                .setCacheControl(cacheControl));
        }
    }    
    ......    

}

​ 看似沒有問題啊，裏面也註冊了， 因爲是內部類，所以繼續分析父類WebMvcAutoConfiguration

@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
// 重點
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
		TaskExecutionAutoConfiguration.class, ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
    
}

​ @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)也就是說，只有在上下文中沒有找到這個WebMvcConfigurationSupport纔會起作用啊 ，而我後來更新的代碼，的確是加了WebMvcConfigurationSupport，導致springboot的webmvc自動裝配失效了，所以，問題居然在這裏，略坑啊

重寫addResourceHandlers

​ 可以肯定的是，自己在WebMvcConfigurationSupport裏面重寫addResourceHandlers添加swagger2應該是沒問題的，代碼如下：

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/statics/**")
            .addResourceLocations("classpath:/statics/");
        registry.addResourceHandler("/swagger-ui.html")
            .addResourceLocations("classpath:/META-INF/resources/");
        registry.addResourceHandler("/webjars/**")
            .addResourceLocations("classpath:/META-INF/resources/webjars/");
}