详解SpringBoot定制@ResponseBody注解返回的Json格式
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。
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*http://www.apache.org/licenses/LICENSE-2.0
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*distributedundertheLicenseisdistributedonan"ASIS"BASIS,
*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
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*limitationsundertheLicense.
*/
packageorg.springframework.web.method.support;
importorg.springframework.core.MethodParameter;
importorg.springframework.lang.Nullable;
importorg.springframework.web.context.request.NativeWebRequest;
/**
*Strategyinterfacetohandlethevaluereturnedfromtheinvocationofa
*handlermethod.
*
*@authorArjenPoutsma
*@since3.1
*@seeHandlerMethodArgumentResolver
*/
publicinterfaceHandlerMethodReturnValueHandler{
/**
*Whetherthegiven{@linkplainMethodParametermethodreturntype}is
*supportedbythishandler.
*@paramreturnTypethemethodreturntypetocheck
*@return{@codetrue}ifthishandlersupportsthesuppliedreturntype;
*{@codefalse}otherwise
*/
booleansupportsReturnType(MethodParameterreturnType);
/**
*Handlethegivenreturnvaluebyaddingattributestothemodeland
*settingavieworsettingthe
*{@linkModelAndViewContainer#setRequestHandled}flagto{@codetrue}
*toindicatetheresponsehasbeenhandleddirectly.
*@paramreturnValuethevaluereturnedfromthehandlermethod
*@paramreturnTypethetypeofthereturnvalue.Thistypemusthave
*previouslybeenpassedto{@link#supportsReturnType}whichmust
*havereturned{@codetrue}.
*@parammavContainertheModelAndViewContainerforthecurrentrequest
*@paramwebRequestthecurrentrequest
*@throwsExceptionifthereturnvaluehandlingresultsinanerror
*/
voidhandleReturnValue(@NullableObjectreturnValue,MethodParameterreturnType,
ModelAndViewContainermavContainer,NativeWebRequestwebRequest)throwsException;
}
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
packagecom.autumn.template;
importlombok.AllArgsConstructor;
importlombok.Getter;
importlombok.NoArgsConstructor;
importlombok.Setter;
importlombok.experimental.Accessors;
/**
*JSON信息交互对象模板
*@AuthorAutumn、
*@Date2019/4/823:46
*@Description
*/
@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain=true)
publicclassResultimplementsBaseBean{
......(这里只展示一些必要字段)
/**响应码*/
privateIntegercode;
/**响应信息*/
privateStringmessage;
/**数据*/
privateObjectdata;
/**请求地址*/
privateStringurl;
......
}
4.2、定义定制Json返回格式Handler
packagecom.autumn.component.handler;
importcom.autumn.template.Result;
importorg.springframework.core.MethodParameter;
importorg.springframework.lang.Nullable;
importorg.springframework.web.context.request.NativeWebRequest;
importorg.springframework.web.method.support.HandlerMethodReturnValueHandler;
importorg.springframework.web.method.support.ModelAndViewContainer;
/**
*统一处理ResponseBody数据格式
*@Author:Autumn、
*@Date:2019/4/2423:59
*@Description:
**/
publicclassResultWarpReturnValueHandlerimplementsHandlerMethodReturnValueHandler{
privatefinalHandlerMethodReturnValueHandlerdelegate;
/**委托*/
publicResultWarpReturnValueHandler(HandlerMethodReturnValueHandlerdelegate){
this.delegate=delegate;
}
/**
*判断返回类型是否需要转成字符串返回
*@paramreturnType方法返回类型
*@return需要转换返回true，否则返回false
*/
@Override
publicbooleansupportsReturnType(MethodParameterreturnType){
returndelegate.supportsReturnType(returnType);
}
/**
*返回值转换
*/
@Override
publicvoidhandleReturnValue(@NullableObjectreturnValue,MethodParameterreturnType,ModelAndViewContainermavContainer,NativeWebRequestwebRequest)throwsException{
//委托SpringMVC默认的RequestResponseBodyMethodProcessor进行序列化
delegate.handleReturnValue(returnValueinstanceofResult?returnValue:Result.succeed(returnValue),returnType,mavContainer,webRequest);
}
}
4.3、替换默认的RequestResponseBodyMethodProcessor
packagecom.autumn.config;
importcom.autumn.component.handler.ResultWarpReturnValueHandler;
importorg.springframework.beans.factory.InitializingBean;
importorg.springframework.beans.factory.annotation.Autowired;
importorg.springframework.cache.annotation.EnableCaching;
importorg.springframework.context.annotation.Configuration;
importorg.springframework.web.method.support.HandlerMethodReturnValueHandler;
importorg.springframework.web.servlet.config.annotation.WebMvcConfigurer;
importorg.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
importorg.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor;
importjava.util.ArrayList;
importjava.util.List;
importlombok.extern.slf4j.Slf4j;
/**
*替换默认的RequestResponseBodyMethodProcessor
*@AuthorAutumn、
*@Date2019/4/823:46
*@Description
*/
@Slf4j
@Configuration
@EnableCaching
publicclassApplicationContextimplementsWebMvcConfigurer,InitializingBean{
@Autowired(required=false)
privateRequestMappingHandlerAdapteradapter;
@Override
publicvoidafterPropertiesSet()throwsException{
//获取SpringMvc的ReturnValueHandlers
ListreturnValueHandlers=adapter.getReturnValueHandlers();
//新建一个List来保存替换后的Handler的List
Listhandlers=newArrayList<>(returnValueHandlers);
//循环遍历找出RequestResponseBodyMethodProcessor
for(HandlerMethodReturnValueHandlerhandler:handlers){
if(handlerinstanceofRequestResponseBodyMethodProcessor){
//创建定制的Json格式处理Handler
ResultWarpReturnValueHandlerdecorator=newResultWarpReturnValueHandler(handler);
//使用定制的Json格式处理Handler替换原有的RequestResponseBodyMethodProcessor
intindex=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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