如何将文件从“assets”文件夹复制到SD卡？

Question

我有一些文件在assets文件夹中。我需要将它们全部复制到一个名为/sdcard/folder的文件夹中。我想要在一个线程内完成此操作。如何做到这一点？

- Rohith Nandakumar

---

你正在寻找这个吗？https://dev59.com/7m855IYBdhLWcg3wQx5L#25988337 - DropAndTrap

在你复制/粘贴下面（很棒！）的解决方案之前，考虑使用这个库在一行代码中完成它：https://dev59.com/7m855IYBdhLWcg3wQx5L#41970539 - JohnnyLambada

Answer 1

如果其他人也遇到了同样的问题，这是我是如何解决的

private void copyAssets() {
    AssetManager assetManager = getAssets();
    String[] files = null;
    try {
        files = assetManager.list("");
    } catch (IOException e) {
        Log.e("tag", "Failed to get asset file list.", e);
    }
    if (files != null) for (String filename : files) {
        InputStream in = null;
        OutputStream out = null;
        try {
          in = assetManager.open(filename);
          File outFile = new File(getExternalFilesDir(null), filename);
          out = new FileOutputStream(outFile);
          copyFile(in, out);
        } catch(IOException e) {
            Log.e("tag", "Failed to copy asset file: " + filename, e);
        }     
        finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    // NOOP
                }
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    // NOOP
                }
            }
        }  
    }
}
private void copyFile(InputStream in, OutputStream out) throws IOException {
    byte[] buffer = new byte[1024];
    int read;
    while((read = in.read(buffer)) != -1){
      out.write(buffer, 0, read);
    }
}

参考：使用Java移动文件

- Rohith Nandakumar

---

要在sd卡中写入文件，您需要在清单文件中授予权限，例如：<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />。 - IronBlossom

我也不会依赖于sdcard位于/sdcard，而是使用Environment.getExternalStorageDirectory()来检索路径。 - Axarydax

应该使用：16*1024（16kb）。我倾向于选择16K或32K作为内存使用和性能之间的良好平衡。 - Nam Vu

@rciovati 在运行时遇到了以下错误：无法复制资产文件：myfile.txt java.io.FileNotFoundException: myfile.txt at android.content.res.AssetManager.openAsset (Native Method)。 - likejudo

只有在我添加以下内容时，这段代码才能正常运行：in = assetManager.open("images-wall/"+filename); 其中 "images-wall" 是我 assets 文件夹中的一个子文件夹。 - Ultimo_m

Answer 2

根据您的解决方案，我自己做了一些工作来允许子文件夹。可能会有人觉得这很有帮助：

...

copyFileOrDir("myrootdir");

...

private void copyFileOrDir(String path) {
    AssetManager assetManager = this.getAssets();
    String assets[] = null;
    try {
        assets = assetManager.list(path);
        if (assets.length == 0) {
            copyFile(path);
        } else {
            String fullPath = "/data/data/" + this.getPackageName() + "/" + path;
            File dir = new File(fullPath);
            if (!dir.exists())
                dir.mkdir();
            for (int i = 0; i < assets.length; ++i) {
                copyFileOrDir(path + "/" + assets[i]);
            }
        }
    } catch (IOException ex) {
        Log.e("tag", "I/O Exception", ex);
    }
}

private void copyFile(String filename) {
    AssetManager assetManager = this.getAssets();

    InputStream in = null;
    OutputStream out = null;
    try {
        in = assetManager.open(filename);
        String newFileName = "/data/data/" + this.getPackageName() + "/" + filename;
        out = new FileOutputStream(newFileName);

        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1) {
            out.write(buffer, 0, read);
        }
        in.close();
        in = null;
        out.flush();
        out.close();
        out = null;
    } catch (Exception e) {
        Log.e("tag", e.getMessage());
    }

}

- DannyA

---

在设备上，assetManager.list(path) 可能会很慢，为了事先创建资产路径列表，可以从 assets 目录使用以下片段：find . -name "*" -type f -exec ls -l {} \; | awk '{print substr($9,3)}' >> assets.list - alexkasko

好的解决方案！唯一需要修复的是在copyFileOrDir()函数开头修剪前导分隔符：path = path.startsWith("/") ? path.substring(1) : path;以使其可用。 - Cross_

这个stackoverflow在某些设备上出现，例如S5。 - behelit

当发生异常时，流不需要关闭吗？ - AndreKR

请将 "/data/data/" + this.getPackageName() 替换为 this.getFilesDir().getAbsolutePath()。 - ibrahimyilmaz

在 finally 块中关闭流。 - Mixaz

Answer 3

上面的解决方案由于一些错误而无法正常工作：

• 目录创建未能成功
• Android 返回的资源还包含三个文件夹：images、sounds 和 webkit
• 新增了处理大文件的方式：在项目中的 assets 文件夹中给文件添加扩展名 .mp3，在复制时目标文件将没有 .mp3 扩展名

以下是代码（我保留了 Log 语句，但您现在可以删除它们）：

final static String TARGET_BASE_PATH = "/sdcard/appname/voices/";

private void copyFilesToSdCard() {
    copyFileOrDir(""); // copy all files in assets folder in my project
}

private void copyFileOrDir(String path) {
    AssetManager assetManager = this.getAssets();
    String assets[] = null;
    try {
        Log.i("tag", "copyFileOrDir() "+path);
        assets = assetManager.list(path);
        if (assets.length == 0) {
            copyFile(path);
        } else {
            String fullPath =  TARGET_BASE_PATH + path;
            Log.i("tag", "path="+fullPath);
            File dir = new File(fullPath);
            if (!dir.exists() && !path.startsWith("images") && !path.startsWith("sounds") && !path.startsWith("webkit"))
                if (!dir.mkdirs())
                    Log.i("tag", "could not create dir "+fullPath);
            for (int i = 0; i < assets.length; ++i) {
                String p;
                if (path.equals(""))
                    p = "";
                else 
                    p = path + "/";

                if (!path.startsWith("images") && !path.startsWith("sounds") && !path.startsWith("webkit"))
                    copyFileOrDir( p + assets[i]);
            }
        }
    } catch (IOException ex) {
        Log.e("tag", "I/O Exception", ex);
    }
}

private void copyFile(String filename) {
    AssetManager assetManager = this.getAssets();

    InputStream in = null;
    OutputStream out = null;
    String newFileName = null;
    try {
        Log.i("tag", "copyFile() "+filename);
        in = assetManager.open(filename);
        if (filename.endsWith(".jpg")) // extension was added to avoid compression on APK file
            newFileName = TARGET_BASE_PATH + filename.substring(0, filename.length()-4);
        else
            newFileName = TARGET_BASE_PATH + filename;
        out = new FileOutputStream(newFileName);

        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1) {
            out.write(buffer, 0, read);
        }
        in.close();
        in = null;
        out.flush();
        out.close();
        out = null;
    } catch (Exception e) {
        Log.e("tag", "Exception in copyFile() of "+newFileName);
        Log.e("tag", "Exception in copyFile() "+e.toString());
    }

}

编辑：更正了一个放错位置的 ";"，导致出现系统性的“无法创建目录”错误。

- Yoram Cohen

---

必须让这成为解决方案！ - Massimo Variolo

注意：Log.i("tag", "could not create dir "+fullPath);总是发生在if语句中分号放错位置的情况下。 - RoundSparrow hilltx

太棒了！非常感谢！但是为什么要检查JPG文件？ - Phuong

Answer 4

我知道这个问题已经有了答案，但我有一种更加优雅的方法将文件从资产目录复制到SD卡上的文件。它不需要“for”循环，而是使用文件流和通道来完成工作。

（注意）如果使用任何类型的压缩文件，例如APK、PDF等，则可能需要在插入资产之前重命名文件扩展名，并在复制到SD卡后重新命名。

AssetManager am = context.getAssets();
AssetFileDescriptor afd = null;
try {
    afd = am.openFd( "MyFile.dat");

    // Create new file to copy into.
    File file = new File(Environment.getExternalStorageDirectory() + java.io.File.separator + "NewFile.dat");
    file.createNewFile();

    copyFdToFile(afd.getFileDescriptor(), file);

} catch (IOException e) {
    e.printStackTrace();
}

一种无需遍历文件的方法来复制文件。

public static void copyFdToFile(FileDescriptor src, File dst) throws IOException {
    FileChannel inChannel = new FileInputStream(src).getChannel();
    FileChannel outChannel = new FileOutputStream(dst).getChannel();
    try {
        inChannel.transferTo(0, inChannel.size(), outChannel);
    } finally {
        if (inChannel != null)
            inChannel.close();
        if (outChannel != null)
            outChannel.close();
    }
}

- JPM

---

这种方法对我来说行不通， "This file can not be opened as a file descriptor; it is probably compressed" -- 这是一个PDF文件。你知道怎么解决吗？ - Gaʀʀʏ

Eclipse提示：资源泄漏：'<未分配Closeable值>'从未关闭。 - behelit

假定inChannel.size()返回文件的大小。它没有这样的保证。我得到了两个文件的2.5 MiB，每个文件都是450 KiB。 - AI0867

我刚刚发现AssetFileDescriptor.getLength()会返回正确的文件大小。 - AI0867

除此之外，资源可能不会从文件描述符的位置0开始。AssetFileDescriptor.getStartOffset()将返回起始偏移量。 - AI0867

Answer 5

这将是Kotlin中简洁的方法。

    fun AssetManager.copyRecursively(assetPath: String, targetFile: File) {
        val list = list(assetPath)
        if (list.isEmpty()) { // assetPath is file
            open(assetPath).use { input ->
                FileOutputStream(targetFile.absolutePath).use { output ->
                    input.copyTo(output)
                    output.flush()
                }
            }

        } else { // assetPath is folder
            targetFile.delete()
            targetFile.mkdir()

            list.forEach {
                copyRecursively("$assetPath/$it", File(targetFile, it))
            }
        }
    }

- cchcc

---

list(assetPath)?.let { ... }，实际上是可空的。 - Gábor

当使用FileOutputStream时，flush()是无用的，因为OutputStream中flush()的实现为空。 - Zhou Hongbo

Answer 6

试试这个，它更简单，这将帮助你：

// Open your local db as the input stream
    InputStream myInput = _context.getAssets().open(YOUR FILE NAME);

    // Path to the just created empty db
    String outFileName =SDCARD PATH + YOUR FILE NAME;

    // Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);

    // transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myInput.read(buffer)) > 0) {
        myOutput.write(buffer, 0, length);
    }
    // Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();

- GOLDEE

Answer 7

这是适用于当前Android设备的清理过的版本，功能性方法设计，可以将其复制到AssetsHelper类中，例如;)

/**
 * 
 * Info: prior to Android 2.3, any compressed asset file with an
 * uncompressed size of over 1 MB cannot be read from the APK. So this
 * should only be used if the device has android 2.3 or later running!
 * 
 * @param c
 * @param targetFolder
 *            e.g. {@link Environment#getExternalStorageDirectory()}
 * @throws Exception
 */
@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public static boolean copyAssets(AssetManager assetManager,
        File targetFolder) throws Exception {
    Log.i(LOG_TAG, "Copying files from assets to folder " + targetFolder);
    return copyAssets(assetManager, "", targetFolder);
}

/**
 * The files will be copied at the location targetFolder+path so if you
 * enter path="abc" and targetfolder="sdcard" the files will be located in
 * "sdcard/abc"
 * 
 * @param assetManager
 * @param path
 * @param targetFolder
 * @return
 * @throws Exception
 */
public static boolean copyAssets(AssetManager assetManager, String path,
        File targetFolder) throws Exception {
    Log.i(LOG_TAG, "Copying " + path + " to " + targetFolder);
    String sources[] = assetManager.list(path);
    if (sources.length == 0) { // its not a folder, so its a file:
        copyAssetFileToFolder(assetManager, path, targetFolder);
    } else { // its a folder:
        if (path.startsWith("images") || path.startsWith("sounds")
                || path.startsWith("webkit")) {
            Log.i(LOG_TAG, "  > Skipping " + path);
            return false;
        }
        File targetDir = new File(targetFolder, path);
        targetDir.mkdirs();
        for (String source : sources) {
            String fullSourcePath = path.equals("") ? source : (path
                    + File.separator + source);
            copyAssets(assetManager, fullSourcePath, targetFolder);
        }
    }
    return true;
}

private static void copyAssetFileToFolder(AssetManager assetManager,
        String fullAssetPath, File targetBasePath) throws IOException {
    InputStream in = assetManager.open(fullAssetPath);
    OutputStream out = new FileOutputStream(new File(targetBasePath,
            fullAssetPath));
    byte[] buffer = new byte[16 * 1024];
    int read;
    while ((read = in.read(buffer)) != -1) {
        out.write(buffer, 0, read);
    }
    in.close();
    out.flush();
    out.close();
}

- Simon

Answer 8

根据@DannyA在SO的回答，对此进行了修改。

private void copyAssets(String path, String outPath) {
    AssetManager assetManager = this.getAssets();
    String assets[];
    try {
        assets = assetManager.list(path);
        if (assets.length == 0) {
            copyFile(path, outPath);
        } else {
            String fullPath = outPath + "/" + path;
            File dir = new File(fullPath);
            if (!dir.exists())
                if (!dir.mkdir()) Log.e(TAG, "No create external directory: " + dir );
            for (String asset : assets) {
                copyAssets(path + "/" + asset, outPath);
            }
        }
    } catch (IOException ex) {
        Log.e(TAG, "I/O Exception", ex);
    }
}

private void copyFile(String filename, String outPath) {
    AssetManager assetManager = this.getAssets();

    InputStream in;
    OutputStream out;
    try {
        in = assetManager.open(filename);
        String newFileName = outPath + "/" + filename;
        out = new FileOutputStream(newFileName);

        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1) {
            out.write(buffer, 0, read);
        }
        in.close();
        out.flush();
        out.close();
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
    }

}

准备工作

在 src/main/assets 中添加名为 fold 的文件夹。

用法

File outDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString());
copyAssets("fold",outDir.toString());

在外部目录中找到所有在assets文件夹内的文件和目录

- Codelaby

Answer 9

在Rohith Nandakumar的方案基础上，我做了一些自己的东西来从assets子文件夹(即"assets/MyFolder")复制文件。同时，在尝试再次复制之前，我会检查文件是否已存在于sdcard中。

private void copyAssets() {
    AssetManager assetManager = getAssets();
    String[] files = null;
    try {
        files = assetManager.list("MyFolder");
    } catch (IOException e) {
        Log.e("tag", "Failed to get asset file list.", e);
    }
    if (files != null) for (String filename : files) {
        InputStream in = null;
        OutputStream out = null;
        try {
          in = assetManager.open("MyFolder/"+filename);
          File outFile = new File(getExternalFilesDir(null), filename);
          if (!(outFile.exists())) {// File does not exist...
                out = new FileOutputStream(outFile);
                copyFile(in, out);
          }
        } catch(IOException e) {
            Log.e("tag", "Failed to copy asset file: " + filename, e);
        }     
        finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    // NOOP
                }
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    // NOOP
                }
            }
        }  
    }
}
private void copyFile(InputStream in, OutputStream out) throws IOException {
    byte[] buffer = new byte[1024];
    int read;
    while((read = in.read(buffer)) != -1){
      out.write(buffer, 0, read);
    }
}

- Pablo Alfonso

Answer 10

利用这个问题中的一些概念，我编写了一个名为AssetCopier的类，使得复制/assets/变得简单。它可以在GitHub上获得，并且可以通过jitpack.io进行访问：

new AssetCopier(MainActivity.this)
        .withFileScanning()
        .copy("tocopy", destDir);

请查看https://github.com/flipagram/android-assetcopier，了解更多详情。

- JohnnyLambada