Use kotlin use to simplify file reading and writing

Use Kotlin USE Simplify file reading and writing

Use Kotlin USE to shorten file reading

Conventional writing

Regular file reading and writing are as follows ;

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

Use Use

Kotlin1.2 Start , Provide a use Extension method , Can be used in Closeable Class
The above code can be reduced to ：

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 = 0
        val buffer = ByteArray(8 * 1024)
        var bytes = inputStream.read(buffer)
        while (bytes >= 0) {
            outputStream.write(buffer, 0, bytes)
            bytesCopied += bytes
            bytes = inputStream.read(buffer)
        }
    }
    PdfReader(file)
}

Benefit time Copy-to

above Stream copy will also have an extension . InputStream.copyTo

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

Benefit time 2 outputStream() Expand

File class There is also an extension function outputStream()

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

WOW , Transformation completed ,12 Line code , Reduced to 3 That's ok .

Extracurricular reading ：

InputStream Read out character string （Text,String)

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