## 使用 Kotlin USE 简化文件读写

## 使用 Kotlin USE 简化文件读写

使用 Kotlin USE 简化文件读写

Use Kotlin USE to shorten file reading

常规写法

常规的文件读写如下；

private val pdfReader by lazy {val file = File(cacheDir, fileName)val outputStream = FileOutputStream(file)try {val inputStream = assets.open(fileName)var bytesCopied: Long = 0val buffer = ByteArray(8 * 1024)var bytes = ad(buffer)while (bytes >= 0) {outputStream.write(buffer, 0, bytes)bytesCopied += bytesbytes = ad(buffer)}} finally {outputStream.close()}PdfReader(file)
}

使用Use

Kotlin1.2开始，提供一个 use扩展方法，可以用在 Closeable类中
上面代码可以精简成：

private val pdfReader by lazy {val file = File(cacheDir, fileName)val outputStream = FileOutputStream(file)outputStream.use { outputStream ->val inputStream = assets.open(fileName)var bytesCopied: Long = 0val buffer = ByteArray(8 * 1024)var bytes = ad(buffer)while (bytes >= 0) {outputStream.write(buffer, 0, bytes)bytesCopied += bytesbytes = ad(buffer)}}PdfReader(file)
}

福利时间 Copy-to

上面的 流拷贝也会一个扩展。

private val pdfReader by lazy {val file = File(cacheDir, fileName)val outputStream = FileOutputStream(file)outputStream.use { fileOut ->assets.open(fileName).copyTo(fileOut)}PdfReader(file)
}

福利时间2 outputStream()扩展

File 类 也有一个扩展函数 outputStream()

private val pdfReader by lazy {val file = File(cacheDir, fileName)file.outputStream().use { fileOut ->assets.open(fileName).copyTo(fileOut)}PdfReader(file)
}

WOW ,改造完成，12行代码，精简成3行。

课外阅读：

InputStream 读取出 字符串 （Text,String)

val myString = inputStream.bufferedReader().use { bufferReader -> bufferReader?.readText() 
}