ResponseBodyAdvice的理解与应用

ResponseBodyAdvice接口类：

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.mvc.method.annotation;

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;

/**
 * Allows customizing the response after the execution of an {@code @ResponseBody}
 * or a {@code ResponseEntity} controller method but before the body is written
 * with an {@code HttpMessageConverter}.
 *
 * <p>Implementations may be registered directly with
 * {@code RequestMappingHandlerAdapter} and {@code ExceptionHandlerExceptionResolver}
 * or more likely annotated with {@code @ControllerAdvice} in which case they
 * will be auto-detected by both.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public interface ResponseBodyAdvice<T> {

	/**
	 * Whether this component supports the given controller method return type
	 * and the selected {@code HttpMessageConverter} type.
	 * @param returnType the return type
	 * @param converterType the selected converter type
	 * @return {@code true} if {@link #beforeBodyWrite} should be invoked;
	 * {@code false} otherwise
	 */
	boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);

	/**
	 * Invoked after an {@code HttpMessageConverter} is selected and just before
	 * its write method is invoked.
	 * @param body the body to be written
	 * @param returnType the return type of the controller method
	 * @param selectedContentType the content type selected through content negotiation
	 * @param selectedConverterType the converter type selected to write to the response
	 * @param request the current request
	 * @param response the current response
	 * @return the body that was passed in or a modified (possibly new) instance
	 */
	T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType,
			ServerHttpRequest request, ServerHttpResponse response);

}

理解：此接口有beforeBodyWrite方法，参数body是响应对象response中的响应体，那么我们就可以用此方法来对响应体做一些统一的操作。比如加密，签名等。
应用实例：

package com.zqsign.app.privatearbitrate.interceptor;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.zqsign.app.privatearbitrate.model.remote.ResponseModel;
import com.zqsign.app.privatearbitrate.model.viewmodel.Response;
import com.zqsign.app.privatearbitrate.util.RsaSign;
import com.zqsign.app.privatearbitrate.util.constants.ZqConfig;
import org.springframework.core.MethodParameter;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import java.util.List;

@Component
@RestControllerAdvice("com.zqsign.app.privatearbitrate.controller.remote")
public class LocalAuthResponseInterceptor implements ResponseBodyAdvice {

    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    /**
     * 响应时添加签名字段
     * 用**私钥加密
     *
     * @param body
     * @param returnType
     * @param selectedContentType
     * @param selectedConverterType
     * @param request
     * @param response
     * @return
     */
    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {

        String bodyStr = JSON.toJSONString(body, SerializerFeature.MapSortField);
        String sign = null;
        if (body != null) {
            sign = RsaSign.sign(bodyStr, ZqConfig.TENANT_PRIVATE_KEY);
        }
        Response resp = (Response) body;
        ResponseModel responseModel = new ResponseModel();
        responseModel.setCode(resp.getCode());
        responseModel.setMessage(resp.getMessage());
        responseModel.setData(resp.getData());
        responseModel.setSign(sign);
        return responseModel;
    }

}

解释：@RestControllerAdvice(“com.zqsign.app.privatearbitrate.controller.remote”)：
表示com.zqsign.app.privatearbitrate.controller.remote此包下的所有响应对象都会经过此拦截器，并对响应体加上签名。