How exactly does bufferedReader() work in Kotlin?

Question

So I'm trying to read data from a .json file in my Android project:

val file = context.assets.open("myfile.json").bufferedReader().readText()

This works fine and successfully prints out my .json file as one String.

However I want to know what exactly is bufferedReader() and why .readText() can't be called directly on the opened .json file.

PS: readText() returns a String. However:

val json2: JSONObject = JSONObject("mystring") returns:

Caused by: org.json.JSONException: Value mystring of type java.lang.String cannot be converted to JSONObject

How does this make sense?

Answer 1

The readText function is defined as an extension on Reader:

public fun Reader.readText(): String {
    val buffer = StringWriter()
    copyTo(buffer)
    return buffer.toString()
}

An InputStream isn't a Reader, so you have to transform it into some Reader:

public inline fun InputStream.reader(charset: Charset = Charsets.UTF_8): InputStreamReader = 
    InputStreamReader(this, charset)

You can use the reader as a buffered reader with the alternative bufferedReader function:

public inline fun InputStream.bufferedReader(charset: Charset = Charsets.UTF_8): BufferedReader = 
    reader(charset).buffered()

Reader and also BufferedReader are part of the Java standard library and the buffered version is described like this:

Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.

In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders...

It basically wraps a Reader and adds support for reading single lines etc.