java - 使用大字节数组下载大文件会导致 "Out of memory"

Question

我想使用流下载 100MB 的文件:
我使用 AsyncTask 类进行下载:

    @Override
    protected Void doInBackground(String... params) {
        try {
            URL url = new URL(params[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();
            inputStream = connection.getInputStream();
            outputStream = new FileOutputStream(new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), params[1]));
            byte[] data = new byte[104857600];
            int length = inputStream.read(data);
            outputStream.write(data, 0, length);
        } catch (Exception e) {
            Log.e(TAG, "Unable to download file with DownloadTask: " + e.getMessage());
        } finally {
            try {
                if (inputStream != null) {
                    inputStream.close();
                }
                if (outputStream != null) {
                    outputStream.close();
                }
                connection.disconnect();
            } catch (Exception e) {
                Log.e(TAG, "Unable to cancel download file with DownloadTask: " + e.getMessage());
            }
        }
        return null;
    }

我确定我使用了以下权限:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

但是当我测试我的应用程序时，它崩溃了，我在 logcat 中看到Out of memory on a 104857616-byte allocation:

10-02 10:28:35.578 29630-2246/com.example.myapp E/dalvikvm-heap: Out of memory on a 104857616-byte allocation.
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime: java.lang.RuntimeException: An error occured while executing doInBackground()
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at android.os.AsyncTask$3.done(AsyncTask.java:299)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.FutureTask.run(FutureTask.java:239)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.lang.Thread.run(Thread.java:856)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:  Caused by: java.lang.OutOfMemoryError
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at com.example.myapp.DownloaderActivity$DownloadTask.doInBackground(DownloaderActivity.java:126)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at com.example.myapp.DownloaderActivity$DownloadTask.doInBackground(DownloaderActivity.java:107)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) 
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) 
10-02 10:28:35.601 29630-2246/com.example.myapp E/AndroidRuntime:     at java.lang.Thread.run(Thread.java:856)

有什么方法可以下载大文件或接受 104857600 字节 (100MB) 吗？

Answer 1

您已将数据作为 block 逐部分写入。系统不会立即为某个操作提供大量内存。

替换这些行:

byte[] data = new byte[104857600];
int length = inputStream.read(data);
outputStream.write(data, 0, length);

作者:

byte [] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead =input.read(buffer)) != -1) {
outputStream .write(buffer, 0,
bytesRead);
}