Kotlin文件读取，使用块不捕获所有异常

Question

I'm doing some file IO with Kotlin and wanted to use those great extension methods provided in the library

  val cacheDir = externalCacheDir
            File(cacheDir, "missingfile.dat")
                    .inputStream()
                    .use {
                       //Use the file in someway
                    }

So this works great when the file is present but if the file is missing, I get a FileNotFoundException .

This is expected. But If I want to correctly handle it I end up breaking that awesome Kotlin syntax by wrapping it in another try catch

So I dug into the code a bit and looked at the inputStream() call

I see this

public inline fun File.inputStream(): FileInputStream {
    return FileInputStream(this)
}

So I thought I'd make my own extension function that does this. Wraps in a try catch so at least its not visible when using it

fun File.inputStreamOrNull(): FileInputStream? {
    return try {
        FileInputStream(this)
    } catch (e: Exception) {
        null
    }
}

However, a null pointer exception is thrown within the use block

 val cacheDir = externalCacheDir
            File(cacheDir, "protsfasfasfaso.mams")
                    .inputStreamOrNull()
                    .use {
                      //Going to use null input stream :O 
                    }

However, the use block does not actually catch this even though the high order function is wrapped in a try catch too which ends up crashing the app

public inline fun <T : Closeable?, R> T.use(block: (T) -> R): R {
    var closed = false
    try {
        return block(this)
    } catch (e: Exception) {
        closed = true
        try {
            this?.close()
        } catch (closeException: Exception) {
        }
        throw e
    } finally {
        if (!closed) {
            this?.close()
        }
    }
}

Anyone got any ideas about this one? I know the quick fix but is there a way around to keep that cool Kotlin style? Thanks for reading

Answer 1

您可以将.use { ... }调用更改为空安全调用（ ?. ），然后它将返回use或null的返回值。