在Android中将文件从内部存储复制到外部存储

问题描述

我的应用（ Android API 15 ）制作图片并将其存储在内部存储器的文件夹中。现在，我想将此文件复制到外部存储器内的另一个文件夹，例如 / SD卡/ MyApp的。我尝试了以下方法：

My app (Android API 15) makes a picture and stores it in the internal memory's folder. Now, I want to copy this file to another folder inside of the external storage, e.g. /sdcard/myapp. I tried the following approaches:

方法＃1：

private void copyFile(File src, File dst) throws IOException {

    File from = new File(src.getPath());
    File to = new File(dst.getPath());
    from.renameTo(to);
}

---

方法＃ 2：

private void copyFile(File src, File dst) throws IOException {

    FileChannel inChannel = null;
    FileChannel outChannel = null;

    try {
        inChannel = new FileInputStream(src).getChannel();
        outChannel = new FileOutputStream(dst).getChannel();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    try {
        inChannel.transferTo(0, inChannel.size(), outChannel);
    } finally {
        if (inChannel != null)
            inChannel.close();
        if (outChannel != null)
            outChannel.close();
    }
}

---

方法＃3：

private void copyFile(File src, File dst) throws IOException {
    FileInputStream inStream = new FileInputStream(src);

    if (!dst.exists()) {
        dst.mkdir();
    }

    if (!dst.canWrite()) {
        System.out.print("CAN'T WRITE");
        return;
    }

    FileOutputStream outStream = new FileOutputStream(dst);
    FileChannel inChannel = inStream.getChannel();
    FileChannel outChannel = outStream.getChannel();
    inChannel.transferTo(0, inChannel.size(), outChannel);
    inStream.close();
    outStream.close();
}

---

这些方法都没有解决我的任务。在检查了一些相关的主题，我发现的唯一建议是验证持久性

---

None of these methods doesn't solve my task. In checked a number of related topics, and the only suggestion I found is to verify the persistence of

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

在 AndroidManifest.xml 中，它确实存在。

方法＃1 完成执行，但不会复制任何文件夹和文件。

The approach #1 finishes the execution, but no folder and files are copied.

在 方法＃2 中，应用程序失败，异常 java.lang.NullPointerException at outChannel = new FileOutputStream（dst）.getChannel（）; ，但对象dst不是null。

In the approach #2, the app fails with the exception java.lang.NullPointerException at outChannel = new FileOutputStream(dst).getChannel();, but the object dst is not a null.

在 方法＃3 中，我决定验证目标对象是否存在，如果需要，它会创建一个文件夹，但是当我检查是否可以写，检查返回 false 。

我尝试了几种其他方法，成功创建了一个空文件夹，但没有真正复制的文件。

I tried a couple of additional approaches, which succeeded to create an empty folder, but no files are really copied.

由于这是我迈向Android的第一步，我觉得我想念一些小事。请指出，如何将文件从一个文件夹复制到Android中的另一个文件夹，包括从内部存储器移动到外部存储器的文件。

Since this is my very first step towards Android, I feel I miss some small thing. Please, point me, how to copy a file from one folder to another folder in Android, including file moving from internal to external memory.

谢谢。

推荐答案

我解决了我的问题。问题出在目标路径中，在原始代码中：

I solved my issue. The problem was in the destination path, in the original code:

File dst = new File(dstPath);

变量 dstPath 拥有完整的目标路径，包括文件的名称，这是错误的。这是正确的代码片段：

the variable dstPath had the full destination path, including the name of the file, which is wrong. Here is the correct code fragment:

String dstPath = Environment.getExternalStorageDirectory() + File.separator + "myApp" + File.separator;
File dst = new File(dstPath);

exportFile(pictureFile, dst);

---

---

private File exportFile(File src, File dst) throws IOException {

    //if folder does not exist
    if (!dst.exists()) {
        if (!dst.mkdir()) {
            return null;
        }
    }

    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
    File expFile = new File(dst.getPath() + File.separator + "IMG_" + timeStamp + ".jpg");
    FileChannel inChannel = null;
    FileChannel outChannel = null;

    try {
        inChannel = new FileInputStream(src).getChannel();
        outChannel = new FileOutputStream(expFile).getChannel();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    try {
        inChannel.transferTo(0, inChannel.size(), outChannel);
    } finally {
        if (inChannel != null)
            inChannel.close();
        if (outChannel != null)
            outChannel.close();
    }

    return expFile;
}

感谢您的提示。

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