我知道这已经回答，但我有一个稍微更优雅的方式从资产目录复制到sdcard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)如果使用任何类型的压缩文件，APK, PDF，…你可能想重命名文件扩展名之前插入到资产，然后重命名一旦你复制到SDcard)

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();
}

一种复制文件而不必循环遍历它的方法。

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();
    }
}

基于Yoram Cohen的回答，这里有一个支持非静态目标目录的版本。

使用copyFileOrDir(getDataDir()， "")来写入应用程序内部存储文件夹/data/data/pkg_name/

Supports subfolders. Supports custom and non-static target directory Avoids copying "images" etc fake asset folders like private void copyFileOrDir(String TARGET_BASE_PATH, String path) { AssetManager assetManager = this.getAssets(); String assets[] = null; try { Log.i("tag", "copyFileOrDir() "+path); assets = assetManager.list(path); if (assets.length == 0) { copyFile(TARGET_BASE_PATH, 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(TARGET_BASE_PATH, p + assets[i]); } } } catch (IOException ex) { Log.e("tag", "I/O Exception", ex); } } private void copyFile(String TARGET_BASE_PATH, 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()); } }

您还可以使用Guava的ByteStream将文件从资产文件夹复制到SD卡。这是我最终得到的解决方案，将文件递归地从资产文件夹复制到SD卡:

/**
 * Copies all assets in an assets directory to the SD file system.
 */
public class CopyAssetsToSDHelper {

    public static void copyAssets(String assetDir, String targetDir, Context context) 
        throws IOException {
        AssetManager assets = context.getAssets();
        String[] list = assets.list(assetDir);
        for (String f : Objects.requireNonNull(list)) {
            if (f.indexOf(".") > 1) { // check, if this is a file
                File outFile = new File(context.getExternalFilesDir(null), 
                    String.format("%s/%s", targetDir, f));
                File parentFile = outFile.getParentFile();
                if (!Objects.requireNonNull(parentFile).exists()) {
                    if (!parentFile.mkdirs()) {
                        throw new IOException(String.format("Could not create directory %s.", 
                            parentFile));
                    }
                }
                try (InputStream fin = assets.open(String.format("%s/%s", assetDir, f));
                     OutputStream fout = new FileOutputStream(outFile)) {
                    ByteStreams.copy(fin, fout);
                }
            } else { // This is a directory
                copyAssets(String.format("%s/%s", assetDir, f), String.format("%s/%s", targetDir, f), 
                    context);
            }
        }
    }

}

如果其他人也有同样的问题，我就是这么做的

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

基于Rohith Nandakumar的解决方案，我自己做了一些事情，从资产的子文件夹中复制文件。“资产/ MyFolder”)。此外，在尝试再次复制之前，我正在检查文件是否已经存在于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);
    }
}

使用AssetManager，它允许读取资产中的文件。然后使用常规的Java IO将文件写入sdcard。

谷歌是你的朋友，搜索一个例子。