精通SpringBoot——第三篇：详解WebMvcConfigurer接口

SpringBoot 确实为我们做了很多事情， 但有时候我们想要自己定义一些Handler，Interceptor，ViewResolver，MessageConverter，该怎么做呢。在Spring Boot 1.5版本都是靠重写WebMvcConfigurerAdapter的方法来添加自定义拦截器，消息转换器等。SpringBoot 2.0 后，该类被标记为@Deprecated。因此我们只能靠实现WebMvcConfigurer接口来实现。接下来让我们来看看这个接口类吧！（列举下常用的方法供参考）

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 实现WebMvcConfigurer接口，
 */
@Configuration
public class WebConfig implements WebMvcConfigurer {

    /**
     * 添加类型转换器和格式化器
     * @param registry
     */
    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addFormatterForFieldType(LocalDate.class, new USLocalDateFormatter());
    }

    /**
     * 跨域支持
     * @param registry
     */
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedOrigins("*")
                .allowCredentials(true)
                .allowedMethods("GET", "POST", "DELETE", "PUT")
                .maxAge(3600 * 24);
    }

    /**
     * 添加静态资源--过滤swagger-api (开源的在线API文档)
     * @param registry
     */
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //过滤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/");

    }
    }

    /**
     * 配置消息转换器--这里我用的是alibaba 开源的 fastjson
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        //1.需要定义一个convert转换消息的对象;
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
        //2.添加fastJson的配置信息，比如：是否要格式化返回的json数据;
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setSerializerFeatures(SerializerFeature.PrettyFormat,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteNullStringAsEmpty,
                SerializerFeature.DisableCircularReferenceDetect,
                SerializerFeature.WriteNullListAsEmpty,
                SerializerFeature.WriteDateUseDateFormat);
        //3处理中文乱码问题
        List<MediaType> fastMediaTypes = new ArrayList<>();
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        //4.在convert中添加配置信息.
        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);
        fastJsonHttpMessageConverter.setFastJsonConfig(fastJsonConfig);
        //5.将convert添加到converters当中.
        converters.add(fastJsonHttpMessageConverter);
    }
  @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new ReqInterceptor()).addPathPatterns("/**");
    }

}

添加一个Interceptor，作为测试

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 请求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);
    }
}

写个controller测试下

@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);
    }
}

请求地址： http://localhost:8080/locale/date ,看看控制台打印信息

//SpringMvc请求处理的执行过程
Interceptor preHandler method is running !
Controller is running !
Interceptor postHandler method is running !
Interceptor afterCompletion method is running !

题外话：从WebMvcConfigurer这个接口中，可以看到JDK8的一些新特性——在接口中新增了default方法和static方法，这两种方法可以有方法体。大家可以业余时间去了解下。这两种新特性为我们编写代码带来了更多改变，让代码变得更加简洁。