SpringBoot 確實為我們做了很多事情， 但有時候我們想要自己定義一些Handler，Interceptor，ViewResolver，MessageConverter，該怎麼做呢。在Spring Boot 1.5版本都是靠重寫WebMvcConfigurerAdapter的方法來新增自定義攔截器，訊息轉換器等。SpringBoot 2.0 後，該類被標記為@Deprecated。因此我們只能靠實現WebMvcConfigurer介面來實現。接下來讓我們來看看這個介面類吧！（列舉下常用的方法供參考）

package com.developlee.config;
 
import com.alibaba.fastjson.serializer.SerializerFeature;
 
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import com.developlee.configurer.USLocalDateFormatter;
import org.springframework.format.FormatterRegistry;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
 
import org.springframework.http.converter.json.JsonbHttpMessageConverter;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
 
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
 
/**
 * @TODO //
 * @Author Lensen
 * @Date 2018/7/21
 * @Description 實現WebMvcConfigurer介面，
 */
@Configuration
public class WebConfig implements WebMvcConfigurer {
 
    /**
     * 新增型別轉換器和格式化器
     * @param registry
     */
    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addFormatterForFieldType(LocalDate.class, new USLocalDateFormatter());
    }
 
    /**
     * 跨域支援
     * @param registry
     */
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedOrigins("*")
                .allowCredentials(true)
                .allowedMethods("GET", "POST", "DELETE", "PUT")
                .maxAge(3600 * 24);
    }
 
    /**
     * 新增靜態資源--過濾swagger-api (開源的線上API文件)
     * @param registry
     */
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //過濾swagger
        registry.addResourceHandler("swagger-ui.html")
                .addResourceLocations("classpath:/META-INF/resources/");
 
        registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/");
 
        registry.addResourceHandler("/swagger-resources/**")
                .addResourceLocations("classpath:/META-INF/resources/swagger-resources/");
 
        registry.addResourceHandler("/swagger/**")
                .addResourceLocations("classpath:/META-INF/resources/swagger*");
 
        registry.addResourceHandler("/v2/api-docs/**")
                .addResourceLocations("classpath:/META-INF/resources/v2/api-docs/");
 
    }
    }
 
    /**
     * 配置訊息轉換器--這裡我用的是alibaba 開源的 fastjson
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        //1.需要定義一個convert轉換訊息的物件;
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
        //2.新增fastJson的配置資訊，比如：是否要格式化返回的json資料;
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setSerializerFeatures(SerializerFeature.PrettyFormat,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteNullStringAsEmpty,
                SerializerFeature.DisableCircularReferenceDetect,
                SerializerFeature.WriteNullListAsEmpty,
                SerializerFeature.WriteDateUseDateFormat);
        //3處理中文亂碼問題
        List<MediaType> fastMediaTypes = new ArrayList<>();
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        //4.在convert中新增配置資訊.
        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);
        fastJsonHttpMessageConverter.setFastJsonConfig(fastJsonConfig);
        //5.將convert新增到converters當中.
        converters.add(fastJsonHttpMessageConverter);
    }
  @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new ReqInterceptor()).addPathPatterns("/**");
    }
 
}
新增一個Interceptor，作為測試

package com.developlee.configurer;
 
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * @TODO //
 * @Author Lensen
 * @Date 2018/7/21
 * @Description 請求Interceptor
 */
public class ReqInterceptor extends HandlerInterceptorAdapter {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("Interceptor preHandler method is running !");
        return super.preHandle(request, response, handler);
    }
 
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("Interceptor postHandler method is running !");
        super.postHandle(request, response, handler, modelAndView);
    }
 
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("Interceptor afterCompletion method is running !");
        super.afterCompletion(request, response, handler, ex);
    }
 
    @Override
    public void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("Interceptor afterConcurrentHandlingStarted method is running !");
        super.afterConcurrentHandlingStarted(request, response, handler);
    }
}

寫個controller測試下

@Controller
@RequestMapping("/locale")
public class LocaleController {
 
    @GetMapping("/date")
    @ResponseBody
    public String locale(Locale locale){
        System.out.println("Controller is running !");
        return "Hello" + USLocalDateFormatter.getPattern(locale);
    }
}

看看控制檯列印資訊

//SpringMvc請求處理的執行過程
Interceptor preHandler method is running !
Controller is running !
Interceptor postHandler method is running !
Interceptor afterCompletion method is running !

題外話：從WebMvcConfigurer這個介面中，可以看到JDK8的一些新特性——在介面中新增了default方法和static方法，這兩種方法可以有方法體。大家可以業餘時間去了解下。這兩種新特性為我們編寫程式碼帶來了更多改變，讓程式碼變得更加簡潔。