java 在 Kotlin 中使用 BufferedReader 的最佳方式
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Best way to use BufferedReader in Kotlin
提问by Akira Kido
So I've just started using Kotlin for Android, and converted my Android Java codes into Kotlin.
所以我刚刚开始在 Android 上使用 Kotlin，并将我的 Android Java 代码转换为 Kotlin。
In one of the conversions, I stumbled upon a BufferedReader, which I would usually write in Java as the following:
在其中一次转换中，我偶然发现了一个 BufferedReader，我通常用 Java 编写如下：
String result = "";
String line = "";
BufferedReader reader = new BufferedReader(someStream);
while ( (line = reader.readLine()) != null ) {
result += line;
}
But in Kotlin, it seems that Kotlin doesn't allow me to assign values to variables in while conditions.
但是在 Kotlin 中，Kotlin 似乎不允许我在 while 条件下为变量赋值。
Currently, I've written the code as the following:
目前，我编写的代码如下：
val reader = BufferedReader(someStream)
var line : String? = ""
while (line != null) {
line = reader.readLine()
result += line
}
which I don't find so elegant and feels prev-gen, despite using Kotlin.
尽管使用了 Kotlin，但我觉得它并不那么优雅并且感觉很像以前的版本。
What would be the best way to use BufferedReader in Kotlin?
在 Kotlin 中使用 BufferedReader 的最佳方法是什么？
回答by miensol
You can use bufferedReaderlike so
你可以bufferedReader像这样使用
val allText = inputStream.bufferedReader().use(BufferedReader::readText)
回答by Jo?o Gon?alves
If you still wanted to read it line by line you could use some extension functions from std lib and do it as follows:
如果您仍然想逐行阅读它，您可以使用 std lib 中的一些扩展函数并按如下方式进行：
val reader = someStream.bufferedReader()
val iterator = reader.linesSequences().iterator()
while(iterator.hasNext()) {
val line = iterator.next()
// do something with line...
}
reader.close()
or alternatively, using a "functional" approach:
或者，使用“功能”方法：
val reader = someStream.bufferedReader()
reader.useLines {
it.map { line -> // do something with line }
}
by using useLines, you don't need to explicitly call close on the reader, the useLines extensions function will do it for you!
通过使用 useLines，您不需要在阅读器上显式调用 close，useLines 扩展函数将为您完成！
Just adding those for reference.. cheers
只是添加那些以供参考..干杯
回答by Angel Koh
you can also try using the "forEachLine" method.
您也可以尝试使用“forEachLine”方法。
val file = File("./folder/test.txt")
file.bufferedReader().forEachLine {
println("value = $it")
}
it'll also automatically close the stream after reading the last line
它还会在阅读最后一行后自动关闭流
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.io/java.io.-reader/index.html
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.io/java.io.-reader/index.html
fun Reader.forEachLine(action: (String) -> Unit)
Iterates through each line of this reader, calls action for each line read and closes the Reader when it's completed.
fun Reader.forEachLine(action: (String) -> Unit)
遍历此读取器的每一行，为读取的每一行调用操作并在完成时关闭读取器。
回答by Chris Ritchie
Another way is to use a for loop:
另一种方法是使用 for 循环：
val reader = BufferedReader(someStream)
for (line in reader.lines()) {
println(line)
}
While is it not as concise as the accepted answer, it will allow you to loop thru and perform some kind of logic without pumping everything into one string as shown below
虽然它不像接受的答案那么简洁，但它允许您循环并执行某种逻辑，而无需将所有内容都放入一个字符串中，如下所示
val allText: String = inputStream.bufferedReader().use(BufferedReader::readText)
回答by Alejandro Moya
Thanks to Jo?o Gon?alves reference to the stdlib I found that you can use forEachLineto traverse the reader if needed.
感谢 Jo?o Gon?alves 对 stdlib 的引用，我发现如果需要，您可以使用forEachLine来遍历阅读器。
回答by reza rahmad
use the code like this
使用这样的代码
val input = conn.inputStream
val allText = input.bufferedReader().use(BufferedReader::readText)
val result = StringBuilder()
result.append(allText)
return result.toString()
} else {
return "unsuccessful"
}
