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。

一、概述

java8之前，WebMvcConfigurerAdapter还是WebMvcConfigurer得空实现抽象类，WebMvcConfigurerAdapter没有被标注为@Deprecated被遗弃的类。

java8新特性 运用之后：

所以今天要说的是 WebMvcConfigurer，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！

package org.springframework.web.servlet.config.annotation;

import java.util.List;
import org.springframework.format.FormatterRegistry;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.validation.MessageCodesResolver;
import org.springframework.validation.Validator;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.HandlerExceptionResolver;

public interface WebMvcConfigurer {
    default void configurePathMatch(PathMatchConfigurer configurer) {
    }

    default void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
    }

    default void configureAsyncSupport(AsyncSupportConfigurer configurer) {
    }

    default void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
    }

    default void addFormatters(FormatterRegistry registry) {
    }

    default void addInterceptors(InterceptorRegistry registry) {
    }

    default void addResourceHandlers(ResourceHandlerRegistry registry) {
    }

    default void addCorsMappings(CorsRegistry registry) {
    }

    default void addViewControllers(ViewControllerRegistry registry) {
    }

    default void configureViewResolvers(ViewResolverRegistry registry) {
    }

    default void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
    }

    default void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> handlers) {
    }

    default void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    }

    default void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
    }

    default void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
    }

    default void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
    }

    @Nullable
    default Validator getValidator() {
        return null;
    }

    @Nullable
    default MessageCodesResolver getMessageCodesResolver() {
        return null;
    }
}

可以看到，这里有很多的空实现，我们只需实现该接口，@Override相应的方法，就可以实现一些你想要的功能。如下：

@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());
    }
}

二、具体案例

2.1配置拦截器

拦截器配置如下所示，InterceptorRegistry 内的addInterceptor需要一个实现HandlerInterceptor接口的拦截器实例，addPathPatterns方法用于设置拦截器的过滤路径规则。

	@Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new ReqInterceptor()).addPathPatterns("/**");
    }

拦截器实现如下：

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * l拦截器实现
 */
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);
    }
}

2.2 配置CORS实现跨域

配置代码如下所示：

	 /**
     * 跨域支持
     */
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedOrigins("*")  //浏览器允许所有的域访问 / 注意 * 不能满足带有cookie的访问,Origin 必须是全匹配
                .allowCredentials(true)   // 允许带cookie访问
                .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS")
                 .allowedHeaders("token")
                .maxAge(3600);
    }

如果还是不能解决问题，那你就需要想办法获取到请求的request和response对象处理一把，比如通过编写filter在response对象中添加响应头：

@Component
public class SessionInterceptor extends HandlerInterceptorAdapter {

    @Autowired
    RedisUtil redisUtil;

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        String origin = request.getHeader("Origin");
        if (StringUtils.hasText(origin)) { //跨域支持
            response.addHeader("Access-Control-Allow-Origin", origin);
        }
		//......
       return super.preHandle(request, response, handler);
    }
}

2.3配置ViewController

这一个配置在之前是经常被使用到的，最经常用到的就是”/”、”/index”路径请求时不通过@RequestMapping配置，而是直接通过配置文件映射指定请求路径到指定View页面，当然也是在请求目标页面时不需要做什么数据处理才可以这样使用，配置内容如下所示：

	 /**
     * 视图控制器配置
     */
    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        super.addViewControllers(registry);
        registry.addViewController("/").setViewName("/index");
	}

2.4配置ViewResolver

 	/**
     * 配置请求视图映射
     */
    @Bean
    public InternalResourceViewResolver resourceViewResolver()
    {
        InternalResourceViewResolver internalResourceViewResolver = new InternalResourceViewResolver();
        //请求视图文件的前缀地址
        internalResourceViewResolver.setPrefix("/WEB-INF/jsp/");
        //请求视图文件的后缀
        internalResourceViewResolver.setSuffix(".jsp");
        return internalResourceViewResolver;
    }
 
    /**
     * 视图配置
     */
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        super.configureViewResolvers(registry);
        registry.viewResolver(resourceViewResolver());
        /*registry.jsp("/WEB-INF/jsp/",".jsp");*/
	}

2.5 配置MessageConverter

这个配置一般针对于Api接口服务程序，配置在请求返回时内容采用什么转换器进行转换，我们最常用到的就是fastJson的转换，配置如下所示：

/**
     * 消息内容转换配置
     * 配置fastJson返回json转换
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        //调用父类的配置
        super.configureMessageConverters(converters);
        //创建fastJson消息转换器
        FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();
        //创建配置类
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        //修改配置返回内容的过滤
        fastJsonConfig.setSerializerFeatures(
                SerializerFeature.DisableCircularReferenceDetect,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteNullStringAsEmpty
        );
        fastConverter.setFastJsonConfig(fastJsonConfig);
        //将fastjson添加到视图消息转换器列表内
        converters.add(fastConverter);
	}

内容转换都是针对面向接口进行编写的实现类，都必须implements HttpMessageConverter接口完成方法的实现。

参考文档：