DeferredResult的超時處理，采用委托機制，也就是在實例DeferredResult時給予一個超時時長（毫秒），同時在onTimeout中委托（傳入）一個新的處理線程（我們可以認為是超時線程）；當超時時間到來，DeferredResult啟動超時線程，超時線程處理業(yè)務(wù)，封裝返回數(shù)據(jù)，給DeferredResult賦值（正確返回的或錯誤返回的）。

這個實例可以對上一個實例的代碼稍作改動即可。

package com.example; import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.web.context.request.async.DeferredResult; public class TimeOutWork implements Runnable{ private final Logger logger = LoggerFactory.getLogger(this.getClass()); private DeferredResult<ResponseMsg<String>> deferredResult; public TimeOutWork(DeferredResult<ResponseMsg<String>> deferredResult) { this.deferredResult = deferredResult; } @Override public void run() { logger.debug('我超時啦!'); ResponseMsg<String> msg = new ResponseMsg<String>(); msg.fail('我超時啦!'); //deferredResult.setResult(msg); deferredResult.setErrorResult(msg); }}二、DeferredResult請求中注冊超時任務(wù)處理

修改第一個請求，修改了兩處，請自己比較

package com.example; import java.util.HashMap;import java.util.Map; import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import org.springframework.web.bind.annotation.ResponseBody;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.context.request.async.DeferredResult; @RestController@RequestMapping('/api')public class DeferredRestController { private final Logger logger = LoggerFactory.getLogger(this.getClass()); private final Map<Integer, DeferredResult<ResponseMsg<String>>> responseBodyMap = new HashMap<Integer, DeferredResult<ResponseMsg<String>>>(); private final Map<Integer, RequestMsg> requestBodyMap = new HashMap<Integer, RequestMsg>(); /** * 第一個請求 * * @param req * @return */ @RequestMapping('/request1') @ResponseBody public DeferredResult<ResponseMsg<String>> request1(RequestMsg req) { logger.debug('request1:請求參數(shù){}', req.getParam()); DeferredResult<ResponseMsg<String>> result =new DeferredResult<ResponseMsg<String>>(10000l);//10秒 result.onTimeout(new TimeOutWork(result));//超時任務(wù) requestBodyMap.put(1, req);// 把請求放到第一個請求map中 responseBodyMap.put(1, result);// 把請求響應(yīng)的DeferredResult實體放到第一個響應(yīng)map中 return result; } /** * 第二個請求 * * @param req * @return */ @RequestMapping('/request2') @ResponseBody public DeferredResult<ResponseMsg<String>> request2(RequestMsg req) { logger.debug('request2:請求參數(shù){}', req.getParam()); DeferredResult<ResponseMsg<String>> result = new DeferredResult<ResponseMsg<String>>(); requestBodyMap.put(2, req);// 把請求放到第二個請求map中 responseBodyMap.put(2, result);// 把請求響應(yīng)的DeferredResult實體放到第二個響應(yīng)map中 return result; } /** * 第三個請求 * * @param req * @return */ @RequestMapping('/request3') @ResponseBody public DeferredResult<ResponseMsg<String>> request3(RequestMsg req) { logger.debug('request3:請求參數(shù){}', req.getParam()); DeferredResult<ResponseMsg<String>> result = new DeferredResult<ResponseMsg<String>>(); requestBodyMap.put(3, req);// 把請求放到第三個請求map中 responseBodyMap.put(3, result);// 把請求響應(yīng)的DeferredResult實體放到第三個響應(yīng)map中 return result; } /** * 控制第x個請求執(zhí)行返回操作，同時自己也返回同樣的值 * * @param x * @return */ @RequestMapping(value = '/requestXReturn', method = RequestMethod.POST) @ResponseBody public ResponseMsg<String> request1Return(Integer x) { ResponseMsg<String> msg = new ResponseMsg<String>(); logger.debug('requestXReturn--1:請求參數(shù){}', x); DeferredResult<ResponseMsg<String>> result = responseBodyMap.get(x); if (result == null) { msg.fail('??!請求已經(jīng)釋放'); return msg; } String resultStr = 'result' + x.toString() + '. Received:' + requestBodyMap.get(x).getParam(); msg.success('成功', resultStr); result.setResult(msg);// 設(shè)置DeferredResult的結(jié)果值，設(shè)置之后，它對應(yīng)的請求進行返回處理 responseBodyMap.remove(x);// 返回map刪除 logger.debug('requestXReturn--2:請求參數(shù){}', x); logger.debug('requestXReturn--3:返回參數(shù){}', msg); return msg; }}三、修改頁面index.html

<script th:src='http://m.b3g6.com/bcjs/@{jquery-1.12.4.min.js}' type='text/javascript'></script> <script th:inline='javascript'> function button1RequestClick(){ var param=$('#request1RequestId').val(); $.ajax({ type:’post’, url:’/api/request1’, dataType : ’json’, data : { ’param’ : param }, success : function(data) { console.log(data); if (data.status==0){ $('#request1ResultId').val(data.data); } else { $('#request1ResultId').val(data.msg); } }, error : function(data) { console.log('button1RequestClick---error'); console.log(data); //alert('錯誤消息：' + data); } }); };

前后的代碼都省略了，其實僅僅修改了

if (data.status==0){ $('#request1ResultId').val(data.data);} else { $('#request1ResultId').val(data.msg);}四、小結(jié)

DeferredResult的超時處理比較簡單，定義時長及注冊一個處理Runnable實例即可。對于setResult、setErrorResult還需要繼續(xù)研究。

1、setResult

2、setErrorResult

3、isSetOrExpired

補充：解決了DeferredResult請求長時間占用數(shù)據(jù)庫連接的問題

最近看了看開源項目appllo配置中心的源碼，發(fā)現(xiàn)一個很有意思的東東：

（1）原理：由于使用了DeferredResult，根據(jù)Spring DispatcherServlet的默認邏輯，數(shù)據(jù)庫連接只有在異步請求真正返回給客戶端的時候才會釋放回連接池

（2）應(yīng)用場景：長連接時間很長，對于大部分請求可能都要數(shù)小時以上才會返回。在這么長的一段時間內(nèi)一直占用著數(shù)據(jù)庫連接是不合理的

@Componentpublic class EntityManagerUtil extends EntityManagerFactoryAccessor { private static final Logger logger = LoggerFactory.getLogger(EntityManagerUtil.class); /** * close the entity manager. * Use it with caution! This is only intended for use with async request, which * Spring won’t close the entity manager until the async request is finished. */ public void closeEntityManager() { EntityManagerHolder emHolder = (EntityManagerHolder) TransactionSynchronizationManager.getResource(getEntityManagerFactory()); if (emHolder == null) { return; } logger.debug('Closing JPA EntityManager in EntityManagerUtil'); EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager()); }}

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持好吧啦網(wǎng)。如有錯誤或未考慮完全的地方，望不吝賜教。