如題所示，原本以為會是一個很簡單的事情，真正上手處理后，發現有很多問題，網上的很多方案，都是部分解決，不夠完善，所以寫了一個工具類，有需要的，直接拿走

• 兼容assets多層嵌套文件夾的場景
• 增加拷貝成功的標識，萬一copy中途失敗的情況下，下次可以再次拷貝

package com.meitu.util

import android.content.res.AssetManager
import android.support.annotation.WorkerThread
import android.text.TextUtils
import com.meitu.library.application.BaseApplication
import java.io.*


/**
 * 從assets復制內容到sd卡的工具類
 * 1、增加復制成功的標識，便于判斷復制中途失敗的場景
 * 2、兼容復制內容嵌套文件夾的場景
 */
class AssetsUtils {
    companion object {
        //復制成功的標記值，故意寫一個無意義的單詞，避免重復
        val sCopySuccessMark = "copySuccessFile_falfjaee"

        /**
         * 從assets目錄復制到素材中心在sd卡的目錄下
         *
         * @param inputPath
         * @return 是否成功處理
         */
        @WorkerThread
        fun copyFromAssetsToMaterialPath(inputPath: String, outputPath: String, maskSuccess: Boolean): Boolean {
            var inputPath = inputPath
            if (TextUtils.isEmpty(inputPath)) {
                return false
            }

            if (inputPath.endsWith(File.separator)) {
                inputPath = inputPath.substring(0, inputPath.length - 1)
            }

            //從assets復制
            val assetManager = BaseApplication.getApplication().assets

            val list: Array<String>?
            try {
                list = assetManager.list(inputPath)
            } catch (e: IOException) {
                return true
            }

            if (list == null || list.size == 0) {
                if (maskSuccess) {
                    val file = File(outputPath, sCopySuccessMark)
                    file.parentFile.mkdirs()
                    file.createNewFile()
                }
                //如果有assets文件不存在，也當做成功，因為默認無效果也會當做素材來處理
                return true
            }

            for (fileName in list) {
                copyAssetsListFile(assetManager, inputPath, fileName, outputPath)
            }

            if (maskSuccess) {
                val file = File(outputPath, sCopySuccessMark)
                file.createNewFile()
            }

            return true
        }


        private fun copyAssetsListFile(assetManager: AssetManager, input: String, fileName: String, output: String) {
            try {
                val innerList = assetManager.list(input + File.separator + fileName)
                if (innerList.isNullOrEmpty()) {
                    copySingleFile(assetManager, input, fileName, output)
                } else {
                    for (innerFile in innerList) {
                        copyAssetsListFile(assetManager, input + File.separator + fileName, innerFile, output + File.separator + fileName)
                    }
                }
            } catch (e: IOException) {
                e.printStackTrace()
            }
        }


        private fun copySingleFile(assetManager: AssetManager, input: String, fileName: String, output: String): Boolean {
            val outFile = File(output, fileName)
            if (!outFile.parentFile.exists()) {
                outFile.parentFile.mkdirs()
            }

            var inputStream: InputStream? = null
            var out: OutputStream? = null

            try {
                inputStream = assetManager.open(input + File.separator + fileName)
                out = FileOutputStream(outFile)

                val buffer = ByteArray(1024)
                var read: Int = inputStream!!.read(buffer)
                while (read != -1) {
                    out.write(buffer, 0, read)
                    read = inputStream!!.read(buffer)
                }
            } catch (e: IOException) {
                return false
            } finally {
                if (inputStream != null) {
                    try {
                        inputStream.close()
                    } catch (e: IOException) {

                    }

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

                    }

                }
            }

            return true
        }
    }

}