SpringBoot使用@ResponseBody注解实现返回的Json格式功能?很多新手对此不是很清楚,为了帮助大家解决这个难题,下面小编将为大家详细讲解,有这方面需求的人可以来学习下,希望你能有所收获。
1、引言
在SpringMVC的使用中,后端与前端的交互一般是使用Json格式进行数据传输,SpringMVC的@ResponseBody注解可以很好的帮助我们进行转换,但是后端返回数据给前端往往都有约定固定的格式,这时候我们在后端返回的时候都要组拼成固定的格式,每次重复的操作非常麻烦。
2、SpringMVC对@ResponseBody的处理
SpringMVC处理@ResponseBody注解声明的Controller是使用默认的.RequestResponseBodyMethodProcessor类来实现,RequestResponseBodyMethodProcessor类实现了HandlerMethodReturnValueHandler接口并实现了接口中的supportsReturnType()和handleReturnValue()方法。
/*
* 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.method.support;
import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.context.request.NativeWebRequest;
/**
* Strategy interface to handle the value returned from the invocation of a
* handler method .
*
* @author Arjen Poutsma
* @since 3.1
* @see HandlerMethodArgumentResolver
*/
public interface HandlerMethodReturnValueHandler {
/**
* Whether the given {@linkplain MethodParameter method return type} is
* supported by this handler.
* @param returnType the method return type to check
* @return {@code true} if this handler supports the supplied return type;
* {@code false} otherwise
*/
boolean supportsReturnType(MethodParameter returnType);
/**
* Handle the given return value by adding attributes to the model and
* setting a view or setting the
* {@link ModelAndViewContainer#setRequestHandled} flag to {@code true}
* to indicate the response has been handled directly.
* @param returnValue the value returned from the handler method
* @param returnType the type of the return value. This type must have
* previously been passed to {@link #supportsReturnType} which must
* have returned {@code true}.
* @param mavContainer the ModelAndViewContainer for the current request
* @param webRequest the current request
* @throws Exception if the return value handling results in an error
*/
void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;
}
3、实现思路
知道@ResponseBody是由RequestResponseBodyMethodProcessor进行处理的,这时候我们可以自己定义一个处理返回数据的Handler来实现我们的定制化Json格式数据返回,但是如果直接把我们定制的Handler加入到SpringMVC的ReturnValueHandlers中,因为我们定制的Handler在RequestResponseBodyMethodProcessor之后,所以我们定制的Handler还是不会生效,这时候我们可以想办法把RequestResponseBodyMethodProcessor替换成我们定制的Handler。
4、代码实现
4.1、定制Json返回格式实体
package com.autumn.template;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.experimental.Accessors;
/**
* JSON信息交互对象模板
* @Author Autumn、
* @Date 2019/4/8 23:46
* @Description
*/
@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class Result implements BaseBean {
......(这里只展示一些必要字段)
/** 响应码 */
private Integer code;
/** 响应信息 */
private String message;
/** 数据 */
private Object data;
/** 请求地址 */
private String url;
......
}
4.2、定义定制Json返回格式Handler
package com.autumn.component.handler;
import com.autumn.template.Result;
import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;
/**
* 统一处理ResponseBody数据格式
* @Author: Autumn、
* @Date: 2019/4/24 23:59
* @Description:
**/
public class ResultWarpReturnValueHandler implements HandlerMethodReturnValueHandler {
private final HandlerMethodReturnValueHandler delegate;
/** 委托 */
public ResultWarpReturnValueHandler(HandlerMethodReturnValueHandler delegate) {
this.delegate = delegate;
}
/**
* 判断返回类型是否需要转成字符串返回
* @param returnType 方法返回类型
* @return 需要转换返回true,否则返回false
*/
@Override
public boolean supportsReturnType(MethodParameter returnType) {
return delegate.supportsReturnType(returnType);
}
/**
* 返回值转换
*/
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
// 委托SpringMVC默认的RequestResponseBodyMethodProcessor进行序列化
delegate.handleReturnValue(returnValue instanceof Result ? returnValue : Result.succeed(returnValue), returnType, mavContainer, webRequest);
}
}
4.3、替换默认的RequestResponseBodyMethodProcessor
package com.autumn.config;
import com.autumn.component.handler.ResultWarpReturnValueHandler;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
import org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor;
import java.util.ArrayList;
import java.util.List;
import lombok.extern.slf4j.Slf4j;
/**
* 替换默认的RequestResponseBodyMethodProcessor
* @Author Autumn、
* @Date 2019/4/8 23:46
* @Description
*/
@Slf4j
@Configuration
@EnableCaching
public class ApplicationContext implements WebMvcConfigurer, InitializingBean {
@Autowired(required = false)
private RequestMappingHandlerAdapter adapter;
@Override
public void afterPropertiesSet() throws Exception {
// 获取SpringMvc的ReturnValueHandlers
List<HandlerMethodReturnValueHandler> returnValueHandlers = adapter.getReturnValueHandlers();
// 新建一个List来保存替换后的Handler的List
List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>(returnValueHandlers);
// 循环遍历找出RequestResponseBodyMethodProcessor
for (HandlerMethodReturnValueHandler handler : handlers) {
if (handler instanceof RequestResponseBodyMethodProcessor) {
// 创建定制的Json格式处理Handler
ResultWarpReturnValueHandler decorator = new ResultWarpReturnValueHandler(handler);
// 使用定制的Json格式处理Handler替换原有的RequestResponseBodyMethodProcessor
int index = handlers.indexOf(handler);
handlers.set(index, decorator);
break;
}
}
// 重新设置SpringMVC的ReturnValueHandlers
adapter.setReturnValueHandlers(handlers);
}
}
5、总结
至此完成了定制@ResponseBody注解返回的Json格式,在Controller中返回任何的字符串都可以定制成为我们想要的Json格式。此外SpringMVC还提供了非常多的Handler接口来进行Controller的增强,可以使用此思路对参数等进行定制化。
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