A utility for performing automatic resource management.
A utility for performing automatic resource management. It can be used to perform an
operation using resources, after which it releases the resources in reverse order
of their creation.
Usage
There are multiple ways to automatically manage resources with Using. If you only need
to manage a single resource, the apply method is easiest; it wraps the
resource opening, operation, and resource releasing in a Try.
If you need to manage multiple resources, Using.Manager should
be used. It allows the managing of arbitrarily many resources, whose creation, use, and
release are all wrapped in a Try.
Example:
import java.io.{BufferedReader, FileReader}
import scala.util.{Try, Using}
val lines: Try[Seq[String]] = Using.Manager { use =>val r1 = use(new BufferedReader(new FileReader("file1.txt")))
val r2 = use(new BufferedReader(new FileReader("file2.txt")))
val r3 = use(new BufferedReader(new FileReader("file3.txt")))
val r4 = use(new BufferedReader(new FileReader("file4.txt")))
// use your resources heredef lines(reader: BufferedReader): Iterator[String] =
Iterator.continually(reader.readLine()).takeWhile(_ != null)
(lines(r1) ++ lines(r2) ++ lines(r3) ++ lines(r4)).toList
}
If you wish to avoid wrapping management and operations in a Try, you can use
Using.resource, which throws any exceptions that occur.
If two exceptions are thrown (e.g., by an operation and closing a resource),
one of them is re-thrown, and the other is
added to it as a suppressed exception.
If the two exceptions are of different 'severities' (see below), the one of a higher
severity is re-thrown, and the one of a lower severity is added to it as a suppressed
exception. If the two exceptions are of the same severity, the one thrown first is
re-thrown, and the one thrown second is added to it as a suppressed exception.
If an exception is a ControlThrowable, or
if it does not support suppression (see
Throwable's constructor with an enableSuppression parameter),
an exception that would have been suppressed is instead discarded.
Exceptions are ranked from highest to lowest severity as follows:
java.lang.VirtualMachineError
java.lang.LinkageError
java.lang.InterruptedException and java.lang.ThreadDeath
When more than two exceptions are thrown, the first two are combined and
re-thrown as described above, and each successive exception thrown is combined
as it is thrown.
A utility for performing automatic resource management. It can be used to perform an operation using resources, after which it releases the resources in reverse order of their creation.
Usage
There are multiple ways to automatically manage resources with
Using
. If you only need to manage a single resource, theapply
method is easiest; it wraps the resource opening, operation, and resource releasing in aTry
.Example:
If you need to manage multiple resources,
Using.Manager
should be used. It allows the managing of arbitrarily many resources, whose creation, use, and release are all wrapped in aTry
.Example:
If you wish to avoid wrapping management and operations in a
Try
, you can useUsing.resource
, which throws any exceptions that occur.Example:
Suppression Behavior
If two exceptions are thrown (e.g., by an operation and closing a resource), one of them is re-thrown, and the other is added to it as a suppressed exception. If the two exceptions are of different 'severities' (see below), the one of a higher severity is re-thrown, and the one of a lower severity is added to it as a suppressed exception. If the two exceptions are of the same severity, the one thrown first is re-thrown, and the one thrown second is added to it as a suppressed exception. If an exception is a
ControlThrowable
, or if it does not support suppression (seeThrowable
's constructor with anenableSuppression
parameter), an exception that would have been suppressed is instead discarded.Exceptions are ranked from highest to lowest severity as follows:
java.lang.VirtualMachineError
java.lang.LinkageError
java.lang.InterruptedException
andjava.lang.ThreadDeath
scala.util.control.ControlThrowable
scala.util.control.ControlThrowable
When more than two exceptions are thrown, the first two are combined and re-thrown as described above, and each successive exception thrown is combined as it is thrown.