释放assets文件夹中文件到内部存储目录

public static void copyAssets(Context context, String oldPath, String newPath) {
        try {
            String fileNames[] = context.getAssets().list(oldPath);// 获取assets目录下的所有文件及目录名
            if (fileNames.length > 0) {// 如果是目录
                File file = new File(newPath);
                file.mkdirs();// 如果文件夹不存在，则递归
                for (String fileName : fileNames) {
                    copyAssets(context, oldPath + "/" + fileName, newPath + "/" + fileName);
                }
            } else {// 如果是文件
                InputStream is = context.getAssets().open(oldPath);
                FileOutputStream fos = new FileOutputStream(new File(newPath));
                byte[] buffer = new byte[1024];
                int byteCount = 0;
                while ((byteCount = is.read(buffer)) != -1) {// 循环从输入流读取
                    // buffer字节
                    fos.write(buffer, 0, byteCount);// 将读取的输入流写入到输出流
                }
                fos.flush();// 刷新缓冲区
                is.close();
                fos.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

调用方式

copyAssets(MainActivity.this,"python3.7.zip","/data/data/"+packageName+"/"+"python3.7.zip");

这里，python3.7.zip为assets文件夹下的文件。
目标文件夹也可以是context.getFilesDir()后的内部存储路径。即"/data/data/"+packageName+"/files/"+"filename"
建议异步处理

AsyncTask.execute(new Runnable() {

            @Override
            public void run() {
                copyAssets(MainActivity.this,"python3.7.zip","/data/data/"+packageName+"/"+"python3.7.zip");
                Toast.makeText(MainActivity.this, "Finish", Toast.LENGTH_SHORT).show();
            }
        });

ps:

private void copyFile(Activity c, String Name,String desPath) throws IOException {  
        File outfile = null;
        if( desPath != null )
            outfile = new File("/data/data/"+getPackageName()+"/files/"+desPath+Name);
        else
            outfile = new File("/data/data/"+getPackageName()+"/files/"+Name); 
        if (!outfile.exists()) {
            outfile.createNewFile();
            FileOutputStream out = new FileOutputStream(outfile);           
            byte[] buffer = new byte[1024];  
            InputStream in;  
            int readLen = 0;  
            if( desPath != null )
                in = c.getAssets().open(desPath+Name);
            else
                in = c.getAssets().open(Name);
            while((readLen = in.read(buffer)) != -1){  
                out.write(buffer, 0, readLen);  
            }  
            out.flush();  
            in.close();  
            out.close();  
        }  
    } 

方式二

亦或使用
源码

package com.example.androidpython;

import android.content.Context;
import android.content.SharedPreferences;
import android.content.res.AssetManager;
import android.preference.PreferenceManager;
import android.util.Log;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;


public class AssetExtractor {

    private final static String LOGTAG = "AssetExtractor";
    private Context mContext;
    private AssetManager mAssetManager;

    public AssetExtractor(Context context) {
        mContext = context;
        mAssetManager = context.getAssets();
    }

    /**
     * Sets a version for the extracted assets version.
     *
     * @param version: int
     */
    public void setAssetsVersion(int version) {
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(mContext);
        SharedPreferences.Editor editor = preferences.edit();

        editor.putInt("assetsVersion", version);
        editor.apply();
    }

    /**
     * Returns the version for the extracted assets.
     *
     * @return int
     */
    public int getAssetsVersion() {
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(mContext);
        return preferences.getInt("assetsVersion", 0);
    }

    /**
     * Returns a list of assets in the APK.
     *
     * @param path: the path in the assets folder.
     * @return the list of assets.
     */
    public List<String> listAssets(String path) {
        List<String> assets = new ArrayList<>();

        try {
            String assetList[] = mAssetManager.list(path);

            if (assetList.length > 0) {
                for (String asset : assetList) {
                    List<String> subAssets = listAssets(path + '/' + asset);
                    assets.addAll(subAssets);
                }
            } else {
                assets.add(path);
            }

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

    /**
     * Returns the path to the assets data dir on the device.
     *
     * @return String with the data dir path.
     */
    public String getAssetsDataDir() {
        String appDataDir = mContext.getApplicationInfo().dataDir;
        return appDataDir + "/assets/";
    }

    /**
     * Copies an asset from the APK to the device.
     *
     * @param src: the source path in the APK.
     * @param dst: the destination path in the device.
     */
    private void copyAssetFile(String src, String dst) {
        File file = new File(dst);
        Log.i(LOGTAG, String.format("Copying %s -> %s", src, dst));

        try {
            File dir = file.getParentFile();
            if (!dir.exists()) {
                dir.mkdirs();
            }

            InputStream in = mAssetManager.open(src);
            OutputStream out = new FileOutputStream(file);
            byte[] buffer = new byte[1024];
            int read = in.read(buffer);
            while (read != -1) {
                out.write(buffer, 0, read);
                read = in.read(buffer);
            }
            out.close();
            in.close();

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

    /**
     * Copies the assets from the APK to the device.
     *
     * @param path: the source path
     */
    public void copyAssets(String path) {
        for (String asset : listAssets(path)) {
            copyAssetFile(asset, getAssetsDataDir() + asset);
        }
    }

    /**
     * Recursively deletes the contents of a folder.
     *
     * @param file: the File object.
     */
    private void recursiveDelete(File file) {
        if (file.isDirectory()) {
            for (File f : file.listFiles())
                recursiveDelete(f);
        }

        Log.i(LOGTAG, "Removing " + file.getAbsolutePath());
        file.delete();
    }

    /**
     * Removes recursively the assets from the device.
     *
     * @param path: the path to the assets folder
     */
    public void removeAssets(String path) {
        File file = new File(getAssetsDataDir() + path);
        recursiveDelete(file);
    }

    /**
     * Returns if the path exists in the device assets.
     *
     * @param path: the path to the assets folder
     * @return Boolean
     */
    public Boolean existsAssets(String path) {
        File file = new File(getAssetsDataDir() + path);
        return file.exists();
    }
}

用法：
(在工程的assets目录创建python文件夹，将所有包复制进该目录，在app启动的适当时候，调用以下代码拷贝assets中(python文件夹内的)的所有文件到手机存储)

// Extract python files from assets
AssetExtractor assetExtractor = new AssetExtractor(MainActivity.this);
assetExtractor.removeAssets("python");
assetExtractor.copyAssets("python");

// Get the extracted assets directory
String pyPath = assetExtractor.getAssetsDataDir() + "python";