Android使用JSON從服務器下載大量數據

Question

我目前希望通過PHP捕獲打印數據來傳輸遠程服務器中的數據，之後將PHP存儲到設備的SQLite數據庫中。

的問題是，有時我需要從表收到超過6.000的行，它不是有效的存儲在設備的RAM內存（變量）所有的數據，所以我在想，如果有人請告訴我如何將傳入的數據保存到設備的內存（sd，資產或資源）中，並在處理到SQLite數據庫後將其刪除。我目前使用接收數據的方法是這樣的：

public JSONArray requestTable(List<NameValuePair> nameValuePairs) throws  ClientProtocolException, IOException, JSONException, UnknownHostException, ConnectTimeoutException 
{ 
    //NameValuePairs contains the Query so it can be catched by php's $_POST 

     HttpClient httpclient = new DefaultHttpClient(); 
    HttpPost httppost = new HttpPost(http://something.php); 
    HttpParams httpparams = new BasicHttpParams(); 

    HttpConnectionParams.setConnectionTimeout(httpparams, msTimeout); 
    JSONArray tableData = null; 
     httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs, HTTP.UTF_8)); 

    HttpResponse httpresponse = httpclient.execute(httppost); 

     Log.i("How are you?", httpresponse.getStatusLine().toString()); 

     HttpEntity entity = httpresponse.getEntity(); 


    if (entity != null) 
    { 
     InputStream instream = entity.getContent(); 
     String result= convertStreamToString(instream); 
      if(result.charAt(0) == '<') 
       Log.e("php error", result); 
      else 
       tableData = new JSONArray(result); 

     instream.close(); 
     httpresponse = null; 
     return tableData; 
    } 

    else 
     return null; 



private static String convertStreamToString(InputStream is) { 

    BufferedReader reader = new BufferedReader(new InputStreamReader(is), 16 * 1024); 
    StringBuilder sb = new StringBuilder(); 

    String line = null; 
    try { 
     while ((line = reader.readLine()) != null) 
     { 
      sb.append(line); 
     } 
    } 
    catch (IOException e) 
    { 
     e.printStackTrace(); 
    } 
    finally 
    { 
     try 
     { 
      is.close(); 
     } 
     catch (IOException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    return sb.toString(); 
} 

通過使用這種方法，我得到這個錯誤：

01-22 17:43:54.098: INFO/dalvikvm-heap(380): Grow heap (frag case) to 18.874MB for 2834992-byte allocation 
01-22 17:44:06.368: INFO/dalvikvm-heap(380): Forcing collection of SoftReferences for 4252484-byte allocation 

01-22 17:44:08.490: ERROR/dalvikvm-heap(380): Out of memory on a 4252484-byte allocation. 
01-22 17:44:08.490: INFO/dalvikvm(380): "Thread-8" prio=5 tid=7 RUNNABLE 
01-22 17:44:08.490: INFO/dalvikvm(380): | group="main" sCount=0 dsCount=0 s=N obj=0x44f182d8 self=0x118bf8 
01-22 17:44:08.490: INFO/dalvikvm(380): | sysTid=389 nice=0 sched=0/0 cgrp=default handle=2525744 
01-22 17:44:08.498: INFO/dalvikvm(380): | schedstat=(328938307540 280414788056 42400) 
01-22 17:44:08.498: INFO/dalvikvm(380): at java.lang.AbstractStringBuilder.enlargeBuffer(AbstractStringBuilder.java:~97) 
01-22 17:44:08.498: INFO/dalvikvm(380): at java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:136) 
01-22 17:44:08.498: INFO/dalvikvm(380): at java.lang.StringBuilder.append(StringBuilder.java:272) 
01-22 17:44:08.498: INFO/dalvikvm(380): at java.io.BufferedReader.readLine(BufferedReader.java:452) 
01-22 17:44:08.498: INFO/dalvikvm(380): at srdroid.cata.Server.convertStreamToString(Server.java:628) 
01-22 17:44:08.498: INFO/dalvikvm(380): at srdroid.cata.Server.requestTable(Server.java:226) 
01-22 17:44:08.498: INFO/dalvikvm(380): at  srdroid.cata.Server$2.run(Server.java:418) 
01-22 17:44:08.498: INFO/dalvikvm(380): at java.lang.Thread.run(Thread.java:1096) 

對不起，長的帖子，任何幫助將不勝感激！

Answer 1

看看Google的GSON Library，特別是JsonReader類。

您可以使用它來逐個元素地「逐出」JSON數據，而不是將整個文檔讀入對象結構（正如您所說的那樣，對內存的影響很大）。然後，您可以一次讀取一行JSON數據並將其寫入數據庫。

JsonReader實際上是來自API級別11的Android的一部分。如果您正在編譯針對較早版本的Android，則可以使用GSON stream jar。