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。

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

基于您的解决方案，我自己做了一些事情来允许子文件夹。有些人可能会觉得这很有用:

...

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());
    }

}

由于一些错误，上述解决方案无法工作:

目录创建失败 Android返回的资产也包含三个文件夹:图像，声音和webkit 增加了处理大文件的方法:在项目的资产文件夹中添加扩展名.mp3到文件，在复制目标文件时将没有.mp3扩展名

下面是代码(我留下了Log语句，但你现在可以删除它们):

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:更正了一个错位的“;”，这是抛出一个系统的“无法创建目录”错误。

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();
    }
}

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();

复制所有文件和目录从资产到您的文件夹!

为了更好地复制，使用apache Commons IO

public void doCopyAssets() throws IOException {
    File externalFilesDir = context.getExternalFilesDir(null);

    doCopy("", externalFilesDir.getPath());

}

//这是复制的主要方法

private void doCopy(String dirName, String outPath) throws IOException {

    String[] srcFiles = assets.list(dirName);//for directory
    for (String srcFileName : srcFiles) {
        String outFileName = outPath + File.separator + srcFileName;
        String inFileName = dirName + File.separator + srcFileName;
        if (dirName.equals("")) {// for first time
            inFileName = srcFileName;
        }
        try {
            InputStream inputStream = assets.open(inFileName);
            copyAndClose(inputStream, new FileOutputStream(outFileName));
        } catch (IOException e) {//if directory fails exception
            new File(outFileName).mkdir();
            doCopy(inFileName, outFileName);
        }

    }
}

public static void closeQuietly(AutoCloseable autoCloseable) {
    try {
        if(autoCloseable != null) {
            autoCloseable.close();
        }
    } catch(IOException ioe) {
        //skip
    }
}

public static void copyAndClose(InputStream input, OutputStream output) throws IOException {
    copy(input, output);
    closeQuietly(input);
    closeQuietly(output);
}

public static void copy(InputStream input, OutputStream output) throws IOException {
    byte[] buffer = new byte[1024];
    int n = 0;
    while(-1 != (n = input.read(buffer))) {
        output.write(buffer, 0, n);
    }
}

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()); } }

嗨，伙计们，我做了这样的事情。 用于n深度复制文件夹和文件复制。 它允许你复制所有的目录结构从Android资产管理器复制:)

    private void manageAssetFolderToSDcard()
    {

        try
        {
            String arg_assetDir = getApplicationContext().getPackageName();
            String arg_destinationDir = FRConstants.ANDROID_DATA + arg_assetDir;
            File FolderInCache = new File(arg_destinationDir);
            if (!FolderInCache.exists())
            {
                copyDirorfileFromAssetManager(arg_assetDir, arg_destinationDir);
            }
        } catch (IOException e1)
        {

            e1.printStackTrace();
        }

    }


    public String copyDirorfileFromAssetManager(String arg_assetDir, String arg_destinationDir) throws IOException
    {
        File sd_path = Environment.getExternalStorageDirectory(); 
        String dest_dir_path = sd_path + addLeadingSlash(arg_destinationDir);
        File dest_dir = new File(dest_dir_path);

        createDir(dest_dir);

        AssetManager asset_manager = getApplicationContext().getAssets();
        String[] files = asset_manager.list(arg_assetDir);

        for (int i = 0; i < files.length; i++)
        {

            String abs_asset_file_path = addTrailingSlash(arg_assetDir) + files[i];
            String sub_files[] = asset_manager.list(abs_asset_file_path);

            if (sub_files.length == 0)
            {
                // It is a file
                String dest_file_path = addTrailingSlash(dest_dir_path) + files[i];
                copyAssetFile(abs_asset_file_path, dest_file_path);
            } else
            {
                // It is a sub directory
                copyDirorfileFromAssetManager(abs_asset_file_path, addTrailingSlash(arg_destinationDir) + files[i]);
            }
        }

        return dest_dir_path;
    }


    public void copyAssetFile(String assetFilePath, String destinationFilePath) throws IOException
    {
        InputStream in = getApplicationContext().getAssets().open(assetFilePath);
        OutputStream out = new FileOutputStream(destinationFilePath);

        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0)
            out.write(buf, 0, len);
        in.close();
        out.close();
    }

    public String addTrailingSlash(String path)
    {
        if (path.charAt(path.length() - 1) != '/')
        {
            path += "/";
        }
        return path;
    }

    public String addLeadingSlash(String path)
    {
        if (path.charAt(0) != '/')
        {
            path = "/" + path;
        }
        return path;
    }

    public void createDir(File dir) throws IOException
    {
        if (dir.exists())
        {
            if (!dir.isDirectory())
            {
                throw new IOException("Can't create directory, a file is in the way");
            }
        } else
        {
            dir.mkdirs();
            if (!dir.isDirectory())
            {
                throw new IOException("Unable to create directory");
            }
        }
    }

最后创建一个Asynctask:

    private class ManageAssetFolders extends AsyncTask<Void, Void, Void>
    {

        @Override
        protected Void doInBackground(Void... arg0)
        {
            manageAssetFolderToSDcard();
            return null;
        }

    }

从你的活动中:

    new ManageAssetFolders().execute();

这里是一个针对当前Android设备的清理版本，功能方法设计，以便您可以将其复制到AssetsHelper类，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();
}

import android.app.Activity;
import android.content.Intent;
import android.content.res.AssetManager;
import android.net.Uri;
import android.os.Environment;
import android.os.Bundle;
import android.util.Log;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        copyReadAssets();
    }


    private void copyReadAssets()
    {
        AssetManager assetManager = getAssets();

        InputStream in = null;
        OutputStream out = null;

        String strDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)+ File.separator + "Pdfs";
        File fileDir = new File(strDir);
        fileDir.mkdirs();   // crear la ruta si no existe
        File file = new File(fileDir, "example2.pdf");



        try
        {

            in = assetManager.open("example.pdf");  //leer el archivo de assets
            out = new BufferedOutputStream(new FileOutputStream(file)); //crear el archivo


            copyFile(in, out);
            in.close();
            in = null;
            out.flush();
            out.close();
            out = null;
        } catch (Exception e)
        {
            Log.e("tag", e.getMessage());
        }

        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(Uri.parse("file://" + Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + File.separator + "Pdfs" + "/example2.pdf"), "application/pdf");
        startActivity(intent);
    }

    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);
        }
    }
}

修改部分代码，如下所示:

out = new BufferedOutputStream(new FileOutputStream(file));

前面的例子是针对pdf文件的，如果是。txt

FileOutputStream fos = new FileOutputStream(file);

轻微修改以上回答复制文件夹递归和适应自定义目的地。

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

private void copyFile(String filename, String destinationDir) {
    AssetManager assetManager = this.getAssets();
    String newFileName = destinationDir + "/" + filename;

    InputStream in = null;
    OutputStream out = null;
    try {
        in = assetManager.open(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());
    }
    new File(newFileName).setExecutable(true, false);
}

修改了@ danya的SO回答

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 /主/资产 添加名称折叠文件夹

使用

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

在外部目录中找到折叠资产内的所有文件和目录

使用这个问题答案中的一些概念，我编写了一个名为assetcopyer的类来简化复制/assets/。它在github上可用，可以通过jitpack.io访问:

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

详情见https://github.com/flipagram/android-assetcopier。

基本上有两种方法。

首先，您可以使用AssetManager。打开和，如Rohith Nandakumar所述，并在输入流上迭代。

其次，您可以使用AssetManager。openFd，它允许你使用一个FileChannel(它有transferTo和transferFrom方法)，所以你不必自己循环输入流。

我将在这里描述openFd方法。

压缩

首先，您需要确保文件以未压缩的方式存储。打包系统可能会选择压缩任何扩展名未标记为noCompress的文件，并且压缩后的文件不能映射到内存中，因此您必须依赖于AssetManager。在那个箱子里打开。

你可以给你的文件添加一个“。mp3”扩展名来阻止它被压缩，但正确的解决方案是修改你的app/build。gradle文件并添加以下行(禁用PDF文件压缩)

aaptOptions {
    noCompress 'pdf'
}

包装文件

请注意，打包器仍然可以将多个文件打包成一个文件，因此您不能只读取AssetManager提供的整个文件。您需要询问AssetFileDescriptor需要哪些部分。

找到已打包文件的正确部分

一旦您确保您的文件存储为未压缩的，您就可以使用AssetManager。openFd方法来获取一个AssetFileDescriptor，它可以用来获取FileInputStream(不像AssetManager. openFd方法)。open，返回一个InputStream)，其中包含一个FileChannel。它还包含起始偏移量(getStartOffset)和大小(getLength)，用于获取文件的正确部分。

实现

下面给出了一个实现示例:

private void copyFileFromAssets(String in_filename, File out_file){
    Log.d("copyFileFromAssets", "Copying file '"+in_filename+"' to '"+out_file.toString()+"'");
    AssetManager assetManager = getApplicationContext().getAssets();
    FileChannel in_chan = null, out_chan = null;
    try {
        AssetFileDescriptor in_afd = assetManager.openFd(in_filename);
        FileInputStream in_stream = in_afd.createInputStream();
        in_chan = in_stream.getChannel();
        Log.d("copyFileFromAssets", "Asset space in file: start = "+in_afd.getStartOffset()+", length = "+in_afd.getLength());
        FileOutputStream out_stream = new FileOutputStream(out_file);
        out_chan = out_stream.getChannel();
        in_chan.transferTo(in_afd.getStartOffset(), in_afd.getLength(), out_chan);
    } catch (IOException ioe){
        Log.w("copyFileFromAssets", "Failed to copy file '"+in_filename+"' to external storage:"+ioe.toString());
    } finally {
        try {
            if (in_chan != null) {
                in_chan.close();
            }
            if (out_chan != null) {
                out_chan.close();
            }
        } catch (IOException ioe){}
    }
}

这个答案是基于摩根大通的答案。

这是目前为止我能在网上找到的最好的解决方案。 我使用了以下链接https://gist.github.com/mhasby/026f02b33fcc4207b302a60645f6e217，但它有一个错误，我修复了，然后它的工作就像一个魅力。 这是我的代码。您可以轻松使用它，因为它是一个独立的java类。

public class CopyAssets {
public static void copyAssets(Context context) {
    AssetManager assetManager = context.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);

            out = new FileOutputStream(Environment.getExternalStorageDirectory()+"/www/resources/" + filename);
            copyFile(in, out);
        } catch(IOException e) {
            Log.e("tag", "Failed to copy asset file: " + filename, e);
        }
        finally {
            if (in != null) {
                try {
                    in.close();
                    in = null;
                } catch (IOException e) {

                }
            }
            if (out != null) {
                try {
                    out.flush();
                    out.close();
                    out = null;
                } catch (IOException e) {

                }
            }
        }
    }
}

public static 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);
    }
}}

As you can see, just create an instance of CopyAssets in your java class which has an activity. Now this part is important, as far as my testing and researching on the internet, You cannot use AssetManager if the class has no activity . It has something to do with the context of the java class. Now, the c.copyAssets(getApplicationContext()) is an easy way to access the method, where c is and instance of CopyAssets class. As per my requirement, I allowed the program to copy all my resource files inside the asset folder to the /www/resources/ of my internal directory. You can easily find out the part where you need to make changes to the directory as per your use. Feel free to ping me if you need any help.

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);
    }
}

对于正在更新到Kotlin的用户:

按照以下步骤避免FileUriExposedExceptions， 假设用户已授予WRITE_EXTERNAL_STORAGE权限，并且您的文件位于assets/pdfs/mypdf.pdf。

private fun openFile() {
    var inputStream: InputStream? = null
    var outputStream: OutputStream? = null
    try {
        val file = File("${activity.getExternalFilesDir(null)}/$PDF_FILE_NAME")
        if (!file.exists()) {
            inputStream = activity.assets.open("$PDF_ASSETS_PATH/$PDF_FILE_NAME")
            outputStream = FileOutputStream(file)
            copyFile(inputStream, outputStream)
        }

        val uri = FileProvider.getUriForFile(
            activity,
            "${BuildConfig.APPLICATION_ID}.provider.GenericFileProvider",
            file
        )
        val intent = Intent(Intent.ACTION_VIEW).apply {
            setDataAndType(uri, "application/pdf")
            addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
            addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY)
        }
        activity.startActivity(intent)
    } catch (ex: IOException) {
        ex.printStackTrace()
    } catch (ex: ActivityNotFoundException) {
        ex.printStackTrace()
    } finally {
        inputStream?.close()
        outputStream?.flush()
        outputStream?.close()
    }
}

@Throws(IOException::class)
private fun copyFile(input: InputStream, output: OutputStream) {
    val buffer = ByteArray(1024)
    var read: Int = input.read(buffer)
    while (read != -1) {
        output.write(buffer, 0, read)
        read = input.read(buffer)
    }
}

companion object {
    private const val PDF_ASSETS_PATH = "pdfs"
    private const val PDF_FILE_NAME = "mypdf.pdf"
}

这在Kotlin中是一种简洁的方式。

    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))
            }
        }
    }

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);
            }
        }
    }

}

这就是我的个性化文本提取类，希望对大家有用。

package lorenzo.morelli.platedetector;

import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;

import com.googlecode.tesseract.android.TessBaseAPI;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class TextExtractor {

    private final Context context;
    private final String dirName;
    private final String language;

    public TextExtractor(final Context context, final String dirName, final String language) {
        this.context = context;
        this.dirName = dirName;
        this.language = language;
    }

    public String extractText(final Bitmap bitmap) {
        final TessBaseAPI tessBaseApi = new TessBaseAPI();
        final String datapath = this.context.getFilesDir()+ "/tesseract/";
        checkFile(new File(datapath + this.dirName + "/"), datapath, this.dirName, this.language);

        tessBaseApi.init(datapath, this.language);
        tessBaseApi.setImage(bitmap);
        final String extractedText = tessBaseApi.getUTF8Text();
        tessBaseApi.end();
        return extractedText;
    }

    private void checkFile(final File dir, final String datapath, final String dirName, final String language) {
        //directory does not exist, but we can successfully create it
        if (!dir.exists()&& dir.mkdirs()) {
            copyFiles(datapath, dirName, language);
        } //The directory exists, but there is no data file in it
        if(dir.exists()) {
            final String datafilepath = datapath + "/" + dirName + "/" + language + ".traineddata";
            final File datafile = new File(datafilepath);
            if (!datafile.exists()) {
                copyFiles(datapath, dirName, language);
            }
        }
    }

    private void copyFiles(final String datapath, final String dirName, final String language) {
        try {
            //location we want the file to be at
            final String filepath = datapath + "/" + dirName + "/" + language + ".traineddata";

            //get access to AssetManager
            final AssetManager assetManager = this.context.getAssets();

            //open byte streams for reading/writing
            final InputStream instream = assetManager.open(dirName + "/" + language + ".traineddata");
            final OutputStream outstream = new FileOutputStream(filepath);

            //copy the file to the location specified by filepath
            byte[] buffer = new byte[1024];
            int read;
            while ((read = instream.read(buffer)) != -1) {
                outstream.write(buffer, 0, read);
            }
            outstream.flush();
            outstream.close();
            instream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

要使用它，你需要训练过的数据文件。你可以从这个链接下载trainddata文件。

一旦你下载了你想要的traineddata文件，你需要在你的Android项目中创建一个名为assets的Android资源目录。在新创建的资产文件夹中，你需要创建一个名为“tessdata”的常规目录，在那里你可以放置你的训练数据文件。 最后你必须初始化MainActivity中的“TextExtractor”类。

final TextExtractor textExtractor = new TextExtractor(this, "tessdata", "eng");

第一个参数是上下文，第二个参数是刚刚创建的目录名，最后一个参数是刚刚下载的训练数据的语言。

要提取文本，你必须调用"extractText"方法:

final String text = textExtractor.extractText(imageWithText);

注意，extractText需要一个位图图像才能工作!! 你可以用这一行从你的可绘制文件中创建一个BitMap图像:

final BitMap image = BitmapFactory.decodeResource(getResources(), R.drawable.test_image);

如果你需要更多的支持，我建议你遵循这个有用的指南:https://github.com/SamVanRoy/Android_OCR_App

你可以用Kotlin在几个步骤中做到这一点，在这里我只复制几个文件，而不是所有从资产到我的应用程序文件目录。

private fun copyRelatedAssets() {
    val assets = arrayOf("myhome.html", "support.css", "myscript.js", "style.css")
    assets.forEach {
        val inputStream = requireContext().assets.open(it)
        val nameSplit = it.split(".")
        val name = nameSplit[0]
        val extension = nameSplit[1]
        val path = inputStream.getFilePath(requireContext().filesDir, name, extension)
        Log.v(TAG, path)
    }
}

这是扩展函数，

fun InputStream.getFilePath(dir: File, name: String, extension: String): String {
    val file = File(dir, "$name.$extension")
    val outputStream = FileOutputStream(file)
    this.copyTo(outputStream, 4096)
    return file.absolutePath
}

洛格猫

/data/user/0/com.***.***/files/myhome.html
/data/user/0/com.***.***/files/support.css
/data/user/0/com.***.***/files/myscript.js
/data/user/0/com.***.***/files/style.css

在Kotlin中，这可以用一行完成!

为InputStream添加扩展乐趣

fun InputStream.toFile(to: File){
    this.use { input->
        to.outputStream().use { out->
            input.copyTo(out)
        }
    }
}

然后使用它

MainActivity.kt

assets.open("test.zip").toFile(File(filesDir,"test.zip"))