在 Android 中发布巨大的 JSON 对象

Question

我想发布一个巨大的 JSON 对象，但是当我尝试时出现此错误：

0 java.lang.OutOfMemoryError
1 at java.lang.String.<init>(String.java:432)
2 at java.lang.AbstractStringBuilder.toString(AbstractStringBuilder.java:642)
3 at java.lang.StringBuffer.toString(StringBuffer.java:723)
4 at java.io.StringWriter.toString(StringWriter.java:100)
5 at com.google.gson.Gson.toJson(Gson.java:528)
6 at com.google.gson.Gson.toJson(Gson.java:507)
7 at dk.companyoung.jobpatrulje.SendDialog$1.onClick(SendDialog.java:87)

这是我的代码：

HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://blabla.dk");

//Making post-objekt
post p = new post();
p.companies = arr;
p.name = activist.getText().toString();
p.phone = cpr.getText().toString();
p.password = "hey";
p.receipt = receipt.getText().toString();


Gson gson = new Gson();

//Its fails here.               
String jsonEn = gson.toJson(p);
httppost.setEntity(new ByteArrayEntity(jsonEn.toString().getBytes("UTF8")));

HttpResponse status = httpclient.execute(httppost);

谁能告诉我出了什么问题，也许给我一个例子:) 那会很好！谢谢大家:)

Answer 1

为避免在处理大型 JSON 对象时出现此错误，您需要使用流式 JSON 解析器 - http://wiki.fasterxml.com/JacksonInFiveMinutes#Streaming_API_Example。其中有两个适用于 Android：GSON 和 Jackson。

我最喜欢的是Jackson

它真的很简单而且很快。但是当然你可以尝试使用GSON:https://sites.google.com/site/gson/streaming

顺便说一句，在 GSON 文档中，您可以找到问题的解释：

 Most applications should use only the object model API. 
 JSON streaming is useful in just a few situations:
 When it is impossible or undesirable to load the entire 
 object model into memory. This is most relevant on mobile 
 platforms where memory is limited.

在我的一个付费 Android 应用程序中，我使用了 Jackson 和 POST 上下文中的大量 JSON 对象，但对于 POST 查询，我使用了 Spring RestTemplate 库。 ：http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/web/client/RestTemplate.html。不知道对你有没有用。这是我使用Jackson 库将巨大的LinkedHashMap 序列化为JSON 并将其发布到远程服务器的代码：

public LinkedHashMap<String, Object>  executeServerCommand
                                (String commandToExecute, LinkedHashMap<String, Object> parameters) 
      {             
 LinkedHashMap<String, Object> resultofOperation =
                             new LinkedHashMap<String, Object>();
    ObjectMapper mapParametersToFromJackson = new ObjectMapper();
    StringWriter stringRepresentation = new StringWriter();
    try {
      mapParametersToFromJackson.writeValue(stringRepresentation, parameters);
    } 
    catch (JsonGenerationException e)
    {
        e.printStackTrace();
    } 
    catch (JsonMappingException e) 
    {
        e.printStackTrace();
    } 
    catch (IOException e) 
    {
        e.printStackTrace();

    }
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
    String postData = "params=" + stringRepresentation.toString();
    requestHeaders.setContentLength(postData.length());
    HttpEntity<String> requestEntity =
              new HttpEntity<String>(postData,requestHeaders);
    HttpComponentsClientHttpRequestFactory preconfiguredHTTPInstance =
                               new HttpComponentsClientHttpRequestFactory();
    RestTemplate restfulRequest = new RestTemplate(preconfiguredHTTPInstance);
    restfulRequest.setRequestFactory(preconfiguredHTTPInstance);
    restfulRequest.getMessageConverters().add(new StringHttpMessageConverter());
    ResponseEntity<String> responseFromServer = restfulRequest.postForEntity(NetworkCommands.MAIN_URL + commandToExecute,
    requestEntity, String.class);
    String serverResponseBody = responseFromServer.getBody();