1 痛点：

       当项目接口多了之后，swagger的扫描时间甚至在整个启动时间占用到三分之二，解决swagger扫描慢的问题，我们将会有更多的时间make bug。

 2 思路：

      让swagger异步扫描初始化，不要卡main 线程，这样就不会影响启动速度。

      优点：启动速度加快， 缺点：启动成功后，刷新swagger ui页面，swagger接口请求不回json来，要等扫描完成后，才能请求回json，swagger才能正常使用。

       特殊说明：如果已经打开了swaggerUI，不刷新swagger UI页面的情况下，不需要去后台重新加载swagger json,不耽误我们测试接口。

 3 实现步骤：

•      不要使用@EnableSwagger2 注解，我们自己实现一个config类，代替这个注解

package com.fhs.module.base.config;

import com.fasterxml.classmate.TypeResolver;
import com.fhs.module.base.swagger.FhsJsonSerializer;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.*;
import org.springframework.plugin.core.config.EnablePluginRegistries;
import springfox.documentation.schema.configuration.ModelsConfiguration;
import springfox.documentation.service.PathDecorator;
import springfox.documentation.spi.service.*;
import springfox.documentation.spi.service.contexts.Defaults;
import springfox.documentation.spring.web.DocumentationCache;
import springfox.documentation.spring.web.ObjectMapperConfigurer;
import springfox.documentation.spring.web.json.JacksonModuleRegistrar;
import springfox.documentation.spring.web.json.JsonSerializer;
import springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper;
import springfox.documentation.spring.web.plugins.DocumentationPluginsManager;
import springfox.documentation.spring.web.scanners.ApiDocumentationScanner;
import springfox.documentation.swagger.configuration.SwaggerCommonConfiguration;
import springfox.documentation.swagger2.annotations.EnableSwagger2;

import javax.servlet.ServletContext;
import java.util.ArrayList;
import java.util.List;


/**
 * 本类代理@EnableSwagger2 注解，可实现swagger异步加载
 */
@Slf4j
@Configuration
@ConditionalOnProperty(prefix = "fhs.swagger", name = "enable", havingValue = "true", matchIfMissing = false)
@Import({  SwaggerCommonConfiguration.class,ModelsConfiguration.class })
@ComponentScan(basePackages = {
        "springfox.documentation.swagger2.web",
        "springfox.documentation.swagger2.mappers",
        "springfox.documentation.spring.web.scanners",
        "springfox.documentation.spring.web.readers.operation",
        "springfox.documentation.spring.web.readers.parameter",
        "springfox.documentation.spring.web.plugins",
        "springfox.documentation.spring.web.paths"
}, excludeFilters =
        {@ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE,
                classes = {DocumentationPluginsBootstrapper.class})})//禁用掉DocumentationPluginsBootstrapper，这样就不会自动扫描，卡主线程
@EnablePluginRegistries({ DocumentationPlugin.class,
        ApiListingBuilderPlugin.class,
        OperationBuilderPlugin.class,
        ParameterBuilderPlugin.class,
        ExpandedParameterBuilderPlugin.class,
        ResourceGroupingStrategy.class,
        OperationModelsProviderPlugin.class,
        DefaultsProviderPlugin.class,
        PathDecorator.class
})
public class SwaggerSyncConfig  implements ApplicationListener<ApplicationReadyEvent> {
    
    @Autowired
    private DocumentationPluginsManager documentationPluginsManager;
    @Autowired
    private RequestHandlerProvider provider;
    @Autowired
    private DocumentationCache scanned;
    @Autowired
    private ApiDocumentationScanner resourceListing;
    @Autowired
    private TypeResolver typeResolver;
    @Autowired
    private Defaults defaults;
    @Autowired
    private ServletContext servletContext;



    @Bean
    public Defaults defaults() {
        return new Defaults();
    }

    @Bean
    public DocumentationCache resourceGroupCache() {
        return new DocumentationCache();
    }

    @Bean
    public static ObjectMapperConfigurer objectMapperConfigurer() {
        return new ObjectMapperConfigurer();
    }

    /**
     * 自定义json序列化，解决value是null的时候依旧序列化问题
     * @param moduleRegistrars 
     * @return
     */
    @Bean
    public JsonSerializer jsonSerializer(List<JacksonModuleRegistrar> moduleRegistrars) {
        return new FhsJsonSerializer(moduleRegistrars);
    }


    @Bean
    public static PropertyPlaceholderConfigurer swaggerProperties() {
        PropertyPlaceholderConfigurer properties = new PropertyPlaceholderConfigurer();
        properties.setIgnoreUnresolvablePlaceholders(true);
        return properties;
    }

    /**
     * 当springboot 项目启动完成后，新启动一个线程去扫描swagger相关注解，生成配置对象
     * @param applicationReadyEvent
     */
    @Override
    public void onApplicationEvent(ApplicationReadyEvent applicationReadyEvent) {
       try{
            List<RequestHandlerProvider> handlerProviders = new ArrayList<>();
            handlerProviders.add(provider);
            new Thread(new Runnable() {
                @Override
                public void run() {
                    // 手动去扫描
                    new DocumentationPluginsBootstrapper(documentationPluginsManager,
                            handlerProviders,scanned,resourceListing,typeResolver,defaults,servletContext).start();
                    log.info("-------------swagger 异步扫描完成-------------");
                }
            }).start();
        }catch (Exception e){
            e.printStackTrace();
        }

    }
}

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import springfox.documentation.spring.web.json.JacksonModuleRegistrar;
import springfox.documentation.spring.web.json.Json;
import springfox.documentation.spring.web.json.JsonSerializer;

import java.util.List;

public class FhsJsonSerializer extends JsonSerializer {
    private ObjectMapper objectMapper = new ObjectMapper();

    public Json toJson(Object toSerialize) {
        try {
            return new Json(objectMapper.writeValueAsString(toSerialize));
        } catch (JsonProcessingException e) {
            throw new RuntimeException("Could not write JSON", e);
        }
    }
    public FhsJsonSerializer(List<JacksonModuleRegistrar> modules) {
        super(modules);
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
    }
}