Android在检索大量数据时OutOfMemoryError

我有一个应用程序，使一个web调用和检索XML数据。如果没有太多的数据，下面的代码可以正常工作。

public class WebClient {
    private static final String TAG = WebClient.class.getSimpleName();
    private String result;

    private static String convertStreamToString(InputStream is) {
        /*
         * To convert the InputStream to String we use the
         * BufferedReader.readLine() method. We iterate until the BufferedReader
         * return null which means there's no more data to read. Each line will
         * appended to a StringBuilder and returned as String.
         */
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line = null;
        try {
            while ((line = reader.readLine()) != null) {
                sb.append(line + "n");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return sb.toString();
    }

    public String connect(String url) {
        Log.e(TAG, "inside LoginWebClient.connect(url). url = " + url);
        result = null;
        HttpClient httpclient = new DefaultHttpClient();
        // Prepare a request object
        HttpGet httpget = new HttpGet(url);

        // Execute the request
        HttpResponse response;
        try { 
            response = httpclient.execute(httpget);
            // Examine the response status
            Log.i(TAG, response.getStatusLine().toString());


            // Get hold of the response entity
            HttpEntity entity = response.getEntity();
            // If the response does not enclose an entity, there is no need
            // to worry about connection release
            if (entity != null) {

                InputStream instream = entity.getContent();
                result = convertStreamToString(instream);
                //Log.i(TAG, result);

                // Closing the input stream will trigger connection release
                instream.close();
            }
                } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Log.e(TAG, "inside WebClient.connect(url). result = " + result);
         return result;
    }//end of connect

如果应用程序使web调用返回大量数据，我得到一个OutOfMemoryError。我已经在谷歌上搜索了这个错误，它可能是由于在StringBuilder的内存中持有过多的数据引起的。

作为一个解决方案，我已经读过，我可以读取流直接到一个字符串，以避免StringBuilder。

我导入了com.google.common.io.CharStreams jar文件到我的项目中，并尝试了以下操作:

private static String convertStreamToStringForGetAlerts(InputStream is) {
        String stringFromStream = null;

        try {
            stringFromStream = CharStreams.toString(new InputStreamReader(is, "UTF-8"));
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return stringFromStream;
    }

但我仍然得到以下错误:

06-05 09:44:40.809: E/AndroidRuntime(5851): FATAL EXCEPTION: AsyncTask #2
06-05 09:44:40.809: E/AndroidRuntime(5851): java.lang.RuntimeException: An error occured while executing doInBackground()
06-05 09:44:40.809: E/AndroidRuntime(5851):     at android.os.AsyncTask$3.done(AsyncTask.java:278)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.lang.Thread.run(Thread.java:856)
06-05 09:44:40.809: E/AndroidRuntime(5851): Caused by: java.lang.OutOfMemoryError
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.lang.AbstractStringBuilder.enlargeBuffer(AbstractStringBuilder.java:94)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:162)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.lang.StringBuilder.append(StringBuilder.java:311)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.lang.StringBuilder.append(StringBuilder.java:44)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.google.common.io.CharStreams.copy(CharStreams.java:204)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.google.common.io.CharStreams.toStringBuilder(CharStreams.java:245)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.google.common.io.CharStreams.toString(CharStreams.java:219)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.carefreegroup.rr3.carefreeoncall.WebClient.convertStreamToStringForGetAlerts(WebClient.java:151)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.carefreegroup.rr3.carefreeoncall.WebClient.connectForGetAlerts(WebClient.java:198)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.carefreegroup.rr3.carefreeoncall.WebService.getAlerts(WebService.java:1778)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.carefreegroup.rr3.carefreeoncall.ShowAlertsActivity$AsyncGetAlerts.doInBackground(ShowAlertsActivity.java:88)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at com.carefreegroup.rr3.carefreeoncall.ShowAlertsActivity$AsyncGetAlerts.doInBackground(ShowAlertsActivity.java:1)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at android.os.AsyncTask$2.call(AsyncTask.java:264)
06-05 09:44:40.809: E/AndroidRuntime(5851):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
06-05 09:44:40.809: E/AndroidRuntime(5851):     ... 4 more

有没有人有任何想法，我如何可以读取这个流成一个字符串，而不会导致这个错误?

作为一个解决方案，我已经读过，我可以读取流直接到一个字符串，以避免StringBuilder。

那没有用。在表面之下，CharStreams方法很可能使用StringBuilder或等效方法…由于它不知道构建器需要多大，它将使用构建器的"双倍大小"策略来扩展后备数组。

将数据读取到内存中最有效的方法是预先分配某种缓冲区(StringBuilder, byte[], char[]等)，其大小足以容纳字符/字节，然后填充缓冲区。如果需要将缓冲区内容转换为String，则仍然需要两倍的内存量。

但这只是避免了不可避免的缩放问题。最终，XML将太大而无法存储在内存中。您真正需要做的是更改代码，使其不试图将整个XML文档保存在内存中。您可以执行以下操作之一:

将其提供给事件驱动的XML解析器(例如SAX)以提取感兴趣的信息，或者
将其写入本地文件，一次写入一个字节、字符、行或缓冲区。

我认为问题是在新的InputStreamReader(....)。为什么不在过程的中间应用字节转换呢?

public byte[] read(InputStream istream)
{
   ByteArrayOutputStream baos = new ByteArrayOutputStream();
   byte[] buffer = new byte[1024]; // Experiment with this value
   int bytesRead;
   while ((bytesRead = istream.read(buffer)) != -1)
   {
      baos.write(buffer, 0, bytesRead);
   }
   return baos.toByteArray();
}

// after the process is run, we call this method with the String
public void readLines(byte[] data)
{
  BufferedReader reader = new BufferedReader(new InputStreamReader(new ByteArrayInputStream(data)));
  String line;
  while ((line = reader.readLine()) != null)
  {
    // do stuff with line
  }
}

你确定你的数据有那么大吗?XML的大小是多少?
无论如何，您必须将数据存入磁盘(首选项、sqlite或文件)，然后逐个块读取或解析缓存的数据。

您可以使用deflater和inflater压缩数据，或者使用n和打印机从服务器发送字符串，然后将数据逐行写入客户机上的临时文件

相关内容

最新更新

热门标签：