自定義統一api返回json格式(app後臺框架搭建三)
在統一json自定義格式的方式有多種:1,[email protected],2,自定義一個註解,自己去解析對象成為json字符串進行返回
第一種方式,我就不推薦,想弄得的話,可以自己去研究一下源碼
第二種方式,主要通過定義註解,通過 HandlerMethodReturnValueHandler 對返回值的處理,而不讓他進去viewResolver處理
==================================================================================
1,講解HandlerMethodReturnValueHandler 處理原理 (簡單介紹,網上資料很多)
2,如何實現自定義統一的json返回格式
==================================================================================
1,HandlerMethodReturnValueHandler
HandlerMethodReturnValueHandler是RequestMappingHandlerAdapter用來處理完映射控制類方法返回的值處理,RequestMappingHandlerAdapter
類包含默認的值處理器鏈的所有處理引擎,默認是會加入handlers.add(new ModelAttributeMethodProcessor(true)); getDefaultReturnValueHandlers()方法裏可以查看到所有默認的處理引擎。
對處理後的對象,會調用RequestMappingHandlerAdapter裏invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod)
方法:
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throwsException { ServletWebRequest webRequest = new ServletWebRequest(request, response); try { WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod); ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod); invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers); invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers); invocableMethod.setDataBinderFactory(binderFactory); invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer); ModelAndViewContainer mavContainer = new ModelAndViewContainer(); mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request)); modelFactory.initModel(webRequest, mavContainer, invocableMethod); mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect); AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); asyncWebRequest.setTimeout(this.asyncRequestTimeout); WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); asyncManager.setTaskExecutor(this.taskExecutor); asyncManager.setAsyncWebRequest(asyncWebRequest); asyncManager.registerCallableInterceptors(this.callableInterceptors); asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors); if (asyncManager.hasConcurrentResult()) { Object result = asyncManager.getConcurrentResult(); mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0]; asyncManager.clearConcurrentResult(); if (logger.isDebugEnabled()) { logger.debug("Found concurrent result value [" + result + "]"); } invocableMethod = invocableMethod.wrapConcurrentResult(result); } invocableMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) { return null; } return getModelAndView(mavContainer, modelFactory, webRequest); } finally { webRequest.requestCompleted(); } }
關鍵是調用 invocableMethod.invokeAndHandle(webRequest, mavContainer);
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs); setResponseStatus(webRequest); if (returnValue == null) { if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) { mavContainer.setRequestHandled(true); return; } } else if (StringUtils.hasText(getResponseStatusReason())) { mavContainer.setRequestHandled(true); return; } mavContainer.setRequestHandled(false); try { this.returnValueHandlers.handleReturnValue( returnValue, getReturnValueType(returnValue), mavContainer, webRequest); } catch (Exception ex) { if (logger.isTraceEnabled()) { logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex); } throw ex; } }
首先設置 mavContainer.setRequestHandled(false);說明是會按處理鏈進行處理,如果設置為true就是處理完就結束了。
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest); 是真正獲取處理鏈,然後從處理鏈中選擇合適的引擎並依次處理。
HandlerMethodReturnValueHandler 只提供兩個接口,
public interface HandlerMethodReturnValueHandler { boolean supportsReturnType(MethodParameter returnType); void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception; }
第一方法是判斷是否支持值處理引擎,第二方法是對值進行處理,並確定是否繼續進行下一個處理引擎執行。
所以,第一個supportsReturnType(MethodParameter returnType)的判斷一定要正確,如果不正確,就永遠不會被執行,這是關鍵。
具體的執行,就可以按這幾個關鍵的類去debug一下就可以了。
-----------------------------------------------------------------------------------------------------------------
2, 具體的實現
2.1 定義註解:用於識別json轉換處理的
import java.lang.annotation.*; /** * Created by ThinkPad on 2017/6/22. */ @Target({ElementType.TYPE,ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface AppResponsBody { String type() default "json"; }
2.2 處理引擎的:需要實現 HandlerMethodReturnValueHandler
/** * Created by ThinkPad on 2017/6/22. */ public class FormatJsonReturnValueHandler implements HandlerMethodReturnValueHandler{ @Override public boolean supportsReturnType(MethodParameter returnType) { System.out.println("===========sdfdsf==============="+ returnType.getMethodAnnotation(AppResponsBody.class)); boolean hasJSONAnno = returnType.getMethodAnnotation(AppResponsBody.class) != null || returnType.getMethodAnnotation(AppResponsBody.class) != null; return hasJSONAnno; } @Override public void handleReturnValue(Object obj, MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest) throws Exception { modelAndViewContainer.setRequestHandled(true); AppResponsBody res=methodParameter.getMethodAnnotation(AppResponsBody.class); String type = res.type(); HttpServletResponse response=nativeWebRequest.getNativeResponse(HttpServletResponse.class); response.setContentType(MediaType.APPLICATION_JSON_UTF8_VALUE); PrintWriter writer = null; Gson gson=new Gson(); ResultInfo info=new ResultInfo(); info.setData(obj); try { writer = response.getWriter(); writer.write(gson.toJson(info)); writer.flush(); } catch (IOException ex) { ex.printStackTrace(); } finally { if (writer != null) writer.close(); } } }
2.3 註冊你編寫的HandlerMethodReturnValueHandler引擎 到webConfig配置文件裏
@Configuration @EnableWebMvc @ComponentScan(basePackages = {"com.ouyang.teson"},useDefaultFilters = true) public class WebConfig extends WebMvcConfigurerAdapter{
配置文件裏增加以下:
@Bean public FormatJsonReturnValueHandler JsonReturnHandler(){ FormatJsonReturnValueHandler formatJsonReturnValueHandler=new FormatJsonReturnValueHandler(); return formatJsonReturnValueHandler; } @Override public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) { returnValueHandlers.add(JsonReturnHandler()); }
另外,還需要定義一個響應類處理統一格式的:ResultInfo.java
public class ResultInfo { public long code; public String message; public Object data; public long getCode() { if(code==0l){ code=200l; } return code; } public void setCode(long code) { this.code = code; } public String getMessage() { if(message==null){ message="處理成功!"; } return message; } public void setMessage(String message) { this.message = message; } public Object getData() { return data; } public void setData(Object data) { this.data = data; } }
至此,我們的所有工作完成,接著進行測試操作:
瀏覽測試結果:
註意:
如果中途有什麽問題,自己可以debug以下,用intellij可以很方便的下載源碼,直接debug,這一點很不錯,這也沒有什麽難度。
下一節,要講的就是怎麽使用spring-boot快速搭建api後臺框架,即是把該配置遷移到spring-boot上並快速啟動。
自定義統一api返回json格式(app後臺框架搭建三)