Using
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
.
Example:
import java.io.{BufferedReader, FileReader}
import scala.util.{Try, Using}
val lines: Try[Seq[String]] =
Using(new BufferedReader(new FileReader("file.txt"))) { reader =>
Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq
}
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 here
def 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.
Example:
import java.io.{BufferedReader, FileReader}
import scala.util.Using
val lines: Seq[String] =
Using.resource(new BufferedReader(new FileReader("file.txt"))) { reader =>
Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq
}
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 (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
andjava.lang.ThreadDeath
fatal exceptions, excluding
scala.util.control.ControlThrowable
scala.util.control.ControlThrowable
all other exceptions
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.
- Source:
- Using.scala
Type members
Classlikes
A resource manager.
- Note:
It is recommended for API designers to require an implicit
Manager
for the creation of custom resources, and to callacquire
during those resources' construction. Doing so guarantees that the resource must be automatically managed, and makes it impossible to forget to do so. Example:class SafeFileReader(file: File)(implicit manager: Using.Manager) extends BufferedReader(new FileReader(file)) { def this(fileName: String)(implicit manager: Using.Manager) = this(new File(fileName)) manager.acquire(this) }
- Companion:
- object
- Source:
- Using.scala
A type class describing how to release a particular type of resource.
A type class describing how to release a particular type of resource.
A resource is anything which needs to be released, closed, or otherwise cleaned up in some way after it is finished being used, and for which waiting for the object's garbage collection to be cleaned up would be unacceptable. For example, an instance of java.io.OutputStream would be considered a resource, because it is important to close the stream after it is finished being used.
An instance of Releasable
is needed in order to automatically manage a resource
with Using
. An implicit instance is provided for all types extending
java.lang.AutoCloseable.
- Type parameters:
- R
the type of the resource
- Companion:
- object
- Source:
- Using.scala
Value members
Concrete methods
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
See the main doc for Using
for full details of
suppression behavior.
- Returns:
a Try containing an exception if one or more were thrown, or the result of the operation if no exceptions were thrown
- Source:
- Using.scala
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
- Type parameters:
- A
the return type of the operation
- R
the type of the resource
- Value parameters:
- body
the operation to perform with the resource
- resource
the resource
- Returns:
the result of the operation, if neither the operation nor releasing the resource throws
- Source:
- Using.scala
Performs an operation using two resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using two resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
- Type parameters:
- A
the return type of the operation
- R1
the type of the first resource
- R2
the type of the second resource
- Value parameters:
- body
the operation to perform using the resources
- resource1
the first resource
- resource2
the second resource
- Returns:
the result of the operation, if neither the operation nor releasing the resources throws
- Source:
- Using.scala
Performs an operation using three resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using three resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
- Type parameters:
- A
the return type of the operation
- R1
the type of the first resource
- R2
the type of the second resource
- R3
the type of the third resource
- Value parameters:
- body
the operation to perform using the resources
- resource1
the first resource
- resource2
the second resource
- resource3
the third resource
- Returns:
the result of the operation, if neither the operation nor releasing the resources throws
- Source:
- Using.scala
Performs an operation using four resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using four resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
- Type parameters:
- A
the return type of the operation
- R1
the type of the first resource
- R2
the type of the second resource
- R3
the type of the third resource
- R4
the type of the fourth resource
- Value parameters:
- body
the operation to perform using the resources
- resource1
the first resource
- resource2
the second resource
- resource3
the third resource
- resource4
the fourth resource
- Returns:
the result of the operation, if neither the operation nor releasing the resources throws
- Source:
- Using.scala