我的 Scala 代码中的文件下载问题 [英] File download problem in my scala code

问题描述

我编写了以下 Scala 代码来下载文件.该文件被正确下载，但也会引发异常.代码如下:

I have written the following scala code to download a file . The file gets downloaded correctly but also an exception is thrown. The code is as follows :

var out:OutputStream = null
var in:InputStream = null

      try {
        var url:URL = null
        url = new URL("http://somehost.com/file.doc")
        val uc = url.openConnection()
        val connection = uc.asInstanceOf[HttpURLConnection]
        connection.setRequestMethod("GET")
        val buffer:Array[Byte] = new Array[Byte](1024)
        var numRead:Int = 0
        in = connection.getInputStream()
        var localFileName="test.doc"
        out = new BufferedOutputStream(new FileOutputStream(localFileName))
        while ((numRead = in.read(buffer)) != -1) {
              out.write(buffer,0,numRead);
        }
      }
      catch {
        case e:Exception => println(e.printStackTrace())
      }

      out.close()
      in.close()

文件已下载，但引发以下异常:

The file gets downloaded but the following exception is thrown :

java.lang.IndexOutOfBoundsException
    at java.io.FileOutputStream.writeBytes(Native Method)
    at java.io.FileOutputStream.write(FileOutputStream.java:260)
    at java.io.BufferedOutputStream.write(BufferedOutputStream.java:105)
    at TestDownload$.main(TestDownload.scala:34)
    at TestDownload.main(TestDownload.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:115)
()

为什么会发生这种情况以及有什么方法可以解决?

Why could this be happening and any way to fix it ?

请帮忙谢谢

推荐答案

Scala 使用赋值语句返回类型 Unit，而不是被赋值的值的类型.所以

Scala returns type Unit, not the type of the value being assigned, with an assignment statement. So

numRead = in.read(buffer)

never 返回 -1;它甚至不返回整数.你可以写

never returns -1; it doesn't even return an integer. You can write

while( { numRead = in.read(buffer); numRead != -1 } ) out.write(buffer, 0, numRead)

或者你可以选择更实用的风格

or you can go for a more functional style with

Iterator.continually(in.read(buffer)).takeWhile(_ != -1).foreach(n => out.write(buffer,0,n))

就我个人而言，我更喜欢前者，因为它更短(并且更少依赖迭代器评估以它应该"的方式发生).

Personally, I prefer the former since it's shorter (and relies less on iterator evaluation happening the way "it ought to").

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