本文介紹了如何在Java中無內存問題地使用REST模板Spring MVC獲取大型JSON的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！
問題描述
當我從REST服務獲得大型JSON時，我收到了java.lang.OutOfMemoyError：Java堆空間…
這發生在~1000次調用REST服務之后
HttpEntity<ProductRequest> requestUpdate = new HttpEntity<>(request, httpHeaders);
ResponseEntity<String> messageEntity = restTemplate.exchange(getEndPointAddress(), HttpMethod.POST, requestUpdate, String.class);
Map<String, Object> map = gson.fromJson(Helper.cleanJson(messageEntity.getBody()), Map.class);
<pre>
java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOfRange(Arrays.java:2694) ~[?:1.7.0_181]
at java.lang.String.<init>(String.java:203) ~[?:1.7.0_181]
at java.lang.StringBuilder.toString(StringBuilder.java:405) ~[?:1.7.0_181]
at org.springframework.util.StreamUtils.copyToString(StreamUtils.java:80) ~[stormjar.jar:4.0.3]
at org.springframework.http.converter.StringHttpMessageConverter.readInternal(StringHttpMessageConverter.java:86) ~[stonjar.jar:4.0.3]
at org.springframework.http.converter.StringHttpMessageConverter.readInternal(StringHttpMessageConverter.java:41) ~[stonjar.jar:4.0.3]
at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:193) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:104) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:884) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:868) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:622) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:580) ~[stonjar.jar:4.0.3]
at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:498) ~[stonjar.jar:4.0.3]
at com.myorg.wcf.PMiddle.retrieveP(PMiddle.java:95) ~[ssar.jar:4.0.3]
at com.myorg.RetrieveP.getPJsonFromService(RetrieveP.java:188) ~[ssar.jar:4.0.3]
at com.myorg.RetrieveP.execute(RetrieveP.java:107) ~[ssar.jar:4.0.3]
at org.apache.storm.daemon.executor$fn__5044$tuple_action_fn__5046.invoke(executor.clj:727) ~[storm-core-1.1.0.jar:1.1.0]
at org.apache.storm.daemon.executor$mk_task_receiver$fn__4965.invoke(executor.clj:459) ~[storm-core-1.1.0.jar:1.1.0]
at org.apache.storm.disruptor$clojure_handler$reify__4480.onEvent(disruptor.clj:40) ~[ss-core-1.1.0.jar:1.1.0]
at org.apache.storm.utils.DisruptorQueue.consumeBatchToCursor(DisruptorQueue.java:472) ~[ss-core-1.1.0.jar:1.1.0]
at org.apache.storm.utils.DisruptorQueue.consumeBatchWhenAvailable(DisruptorQueue.java:451) ~[ss-core-1.1.0.jar:1.1.0]
at org.apache.storm.disruptor$consume_batch_when_available.invoke(disruptor.clj:73) ~[ss-core-1.1.0.jar:1.1.0]
at org.apache.storm.daemon.executor$fn__5044$fn__5057$fn__5110.invoke(executor.clj:846) ~[ss-core-1.1.0.jar:1.1.0]
at org.apache.storm.util$async_loop$fn__557.invoke(util.clj:484) [ss-core-1.1.0.jar:1.1.0]
at clojure.lang.AFn.run(AFn.java:22) [clojure-1.7.0.jar:?]
at java.lang.Thread.run(Thread.java:748) [?:1.7.0_181]</pre>
推薦答案
RestTemplate和底層的SpringBean不是為流處理而設計的，它們在內存中構建整個ResponsEntity。根據您的示例，您沒有按預期使用RestTemplate。您正在讀取String，而不是將響應對象Map<String, Object>反序列化委托給基礎轉換器Bean。
如果JSON響應實在太大，無法放入堆中，您可以將RestTemplate替換為URLConnection或任何其他允許您直接訪問響應的HTTP客戶端庫。這將允許您手動讀取和解析響應，例如by using com.google.gson.stream.JsonReader：
URLConnection conn = // create and open
JsonReader reader = new JsonReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));
// read manually using reader
通過避免包含整個JSON正文的一個大String對象，您將能夠以這種方式節省內存。
這篇關于如何在Java中無內存問題地使用REST模板Spring MVC獲取大型JSON的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，
