如何表示Scala'的*finally*等价物;试一试?
如何使用新的如何表示Scala'的*finally*等价物;试一试?,scala,Scala,如何使用新的TryAPI将以下Java代码转换为Scala public byte[] deflate(byte[] data) { ByteArrayOutputStream outputStream = null; GZIPOutputStream gzipOutputStream = null; try { outputStream = new ByteArrayOutputStream(); gzipOutputStream =
Try
API将以下Java代码转换为Scala
public byte[] deflate(byte[] data) {
ByteArrayOutputStream outputStream = null;
GZIPOutputStream gzipOutputStream = null;
try {
outputStream = new ByteArrayOutputStream();
gzipOutputStream = new GZIPOutputStream(outputStream);
gzipOutputStream.write(data);
return outputStream.toByteArray();
catch (Exception e) {
...
} finally {
if (gzipOutputStream != null) gzipOutputStream.close();
}
}
Scala版本应该是这样的
def deflate(data Array[Byte]): Try[Array[Byte]] = Try {
ByteArrayOutputStream outputStream = new ByteArrayOutputStream()
new GZIPOutputStream(outputStream).write(data)
outputStream.toByteArray
}
。。。但是如何实现Java的
finally
等价物呢?Scala的Try
API不应该直接等价于Java中的Try-catch-finally
构造。事实上,为什么会这样?Scala也内置了try-catch-finally
构造。您可以像在Java中一样直接使用它<当您需要组合多个可能失败的操作时,需要“代码>尝试”
事实上,您提出了更复杂的问题—资源管理。实际上,您的代码应该是这样的:
try (ByteArrayOutputStream os = new ByteArrayOutputStream(data);
GZIPOutputStream gzos = new GZIPOutputStream(os)) {
gzipOutputStream.write(data);
return outputStream.toByteArray();
} catch (Exception e) {
...
}
implicit class TryHasFinally[T](val value:Try[T]) extends AnyVal {
import scala.util.control.NonFatal
def Finally(action: => Unit) : Try[T] =
try {
action;
value
} catch {
case NonFatal(cause) => Failure[T](cause)
}
}
import java.io._
import java.util.zip._
def deflate(data: Array[Byte]): Try[Array[Byte]] = {
var outputStream : ByteArrayOutputStream = null
Try {
outputStream = new ByteArrayOutputStream()
new GZIPOutputStream(outputStream).write(data)
outputStream.toByteArray
} Finally {
outputStream.close()
}
}
Java中的“try with resources”语言特性会自动关闭在try
后面括号中指定的所有资源
不幸的是,Scala在库或语言中还没有直接的等价物。但由于Scala更具表现力,您可以手动编写此构造,也可以使用第三方库,我推荐使用第三方库。有关更多信息,请参见以下链接:
try (ByteArrayOutputStream os = new ByteArrayOutputStream(data);
GZIPOutputStream gzos = new GZIPOutputStream(os)) {
gzipOutputStream.write(data);
return outputStream.toByteArray();
} catch (Exception e) {
...
}
implicit class TryHasFinally[T](val value:Try[T]) extends AnyVal {
import scala.util.control.NonFatal
def Finally(action: => Unit) : Try[T] =
try {
action;
value
} catch {
case NonFatal(cause) => Failure[T](cause)
}
}
import java.io._
import java.util.zip._
def deflate(data: Array[Byte]): Try[Array[Byte]] = {
var outputStream : ByteArrayOutputStream = null
Try {
outputStream = new ByteArrayOutputStream()
new GZIPOutputStream(outputStream).write(data)
outputStream.toByteArray
} Finally {
outputStream.close()
}
}
请注意,按照所有Try方法的精神,如果您的操作引发非致命异常,则不会引发异常,而只是将其捕获为失败
您可以这样使用它:
try (ByteArrayOutputStream os = new ByteArrayOutputStream(data);
GZIPOutputStream gzos = new GZIPOutputStream(os)) {
gzipOutputStream.write(data);
return outputStream.toByteArray();
} catch (Exception e) {
...
}
implicit class TryHasFinally[T](val value:Try[T]) extends AnyVal {
import scala.util.control.NonFatal
def Finally(action: => Unit) : Try[T] =
try {
action;
value
} catch {
case NonFatal(cause) => Failure[T](cause)
}
}
import java.io._
import java.util.zip._
def deflate(data: Array[Byte]): Try[Array[Byte]] = {
var outputStream : ByteArrayOutputStream = null
Try {
outputStream = new ByteArrayOutputStream()
new GZIPOutputStream(outputStream).write(data)
outputStream.toByteArray
} Finally {
outputStream.close()
}
}
请注意,您不必在Finally中检查null,因为如果出于某种难以理解的原因,outputStream为null,那么您将得到一个失败(NullPointerException)。此外,如果close抛出IOException,您将得到一个失败(IOException) Choppy的Lazy TryClose monad是为这种您想尝试使用资源的场景而设计的。另外,它很懒,所以你可以写东西 以下是您将如何使用它的示例:
val output = for {
outputStream <- TryClose(new ByteArrayOutputStream())
gzipOutputStream <- TryClose(new GZIPOutputStream(outputStream))
_ <- TryClose.wrap(gzipOutputStream.write(data))
} yield wrap(outputStream.toByteArray())
// Does not actually run anything until you do this:
output.resolve.unwrap match {
case Success(bytes) => // do something with bytes
case Failure(e) => // handle exception
}
val输出=for{
outputStream可能是您应该使用scala arm的副本。非常有趣……但如果是非致命性的,我不会返回失败,因为这将阻止deflate()返回压缩输出,如果出于任何原因outputStream.close()的话失败…Finally块用于关闭输出流,而不管Try块是否成功。如果关闭ByteArrayOutputStream失败,则会出现严重错误,不返回压缩输出是您最不担心的问题。创建或关闭类似ByteArrayOutputStream的内容会失败的唯一原因是一个OutOfMemoryError,这当然是致命的,在任何情况下都需要抛出。是的,它看起来像是scala arm提供了我想要的功能…我希望它能集成到正式的scala发行版中。