在Spring微服务的开发项目过程中，经常会对返回的结果进行统一包装，需要在每个接口后都需要申明一个包装的返回类型，然后在很多时候，大家都不会按照规范进行操作，或者有时候会忘记，直接返回的对象。可以利用ResponseBodyAdvice对返回的结果，进行统一的包装。

ScioResponseBodyAdvice

package com.scio.core.config.web;

import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import com.scio.core.config.web.WebMvcConfig.StringOrMappingJackson2HttpMessageConverter;

import lombok.extern.slf4j.Slf4j;

@Slf4j
@ControllerAdvice
public class ScioResponseBodyAdvice implements ResponseBodyAdvice<Object> {

    @Override
    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
        return !returnType.getMethod().getReturnType().isAssignableFrom(Void.TYPE)
            && converterType.isAssignableFrom(StringOrMappingJackson2HttpMessageConverter.class);
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
        Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
        ServerHttpResponse response) {
        if (log.isDebugEnabled()) {
            log.debug("advice by ScioResponseBodyAdvice");
        }
        return Resp.success(body);
    }

}

WebMvcConfig

package com.scio.core.config.web;

import java.io.IOException;
import java.lang.reflect.Type;
import java.util.List;

import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;

@Configuration
public class WebMvcConfig extends WebMvcConfigurationSupport {

    @Override
    protected RequestMappingHandlerMapping createRequestMappingHandlerMapping() {
        return new ApiVersionHandlerMapping();
    }
    // 这里需要注意，因为默认的convert是String，如果方法返回的是String，那么将会被提前返回，所以需要做一下兼容。
    @Override
    protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(0, new StringOrMappingJackson2HttpMessageConverter());
        super.extendMessageConverters(converters);
    }

    /**
     * 兼容String和对象类型
     * 
     * @author Wang.ch
     * @date 2019/12/12
     */
    public static class StringOrMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {

        private static final StringHttpMessageConverter shmc = new StringHttpMessageConverter();

        @Override
        public boolean canWrite(Class<?> clazz, MediaType mediaType) {
            boolean canWrite = super.canWrite(clazz, mediaType);
            if (!canWrite) {
                canWrite = clazz.isAssignableFrom(String.class);
            }
            return canWrite;
        }

        @Override
        protected void writeInternal(Object object, Type type, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {
            if (object != null && object instanceof String) {
                outputMessage.getHeaders().setContentType(MediaType.TEXT_PLAIN);;
                shmc.write((String)object, MediaType.TEXT_PLAIN, outputMessage);
                return;
            }
            outputMessage.getHeaders().setContentType(MediaType.APPLICATION_JSON_UTF8);
            super.writeInternal(object, object != null ? object.getClass() : null, outputMessage);
        }
    }
}

TestController

package com.scio.core.config.web;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestController {
    @RequestMapping("/test")
    @ApiVersion("1.0")
    public void test() {
        System.out.println("test");
    }

    @RequestMapping("/test")
    @ApiVersion("2.0")
    public String test2() {
        return "你好";
    }

    @RequestMapping("/test")
    @ApiVersion("3.0")
    public Integer test3() {
        return 1111;
    }
    
    @RequestMapping("/test")
    @ApiVersion("4.0")
    public Resp<String> test4() {
        return Resp.badrequest("test");
    }
}