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 and java.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.

Linear Supertypes

AnyRef, Any

Type Members

final class Manager extends AnyRef

A resource manager.
A resource manager.
Resources can be registered with the manager by calling acquire; such resources will be released in reverse order of their acquisition when the manager is closed, regardless of any exceptions thrown during use.
See the main doc for Using for full details of suppression behavior.
Note
It is recommended for API designers to require an implicit Manager for the creation of custom resources, and to call acquire 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) }
trait Releasable[-R] extends AnyRef

A typeclass describing how to release a particular type of resource.
A typeclass 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.
R
the type of the resource

Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
object Manager
object Releasable
def apply[R, A](resource: ⇒ R)(f: (R) ⇒ A)(implicit arg0: Releasable[R]): Try[A]

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
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
def resource[R, A](resource: R)(body: (R) ⇒ A)(implicit releasable: Releasable[R]): A

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.
R
the type of the resource
A
the return type of the operation
resource
the resource
body
the operation to perform with the resource
returns
the result of the operation, if neither the operation nor releasing the resource throws
def resources[R1, R2, R3, R4, A](resource1: R1, resource2: ⇒ R2, resource3: ⇒ R3, resource4: ⇒ R4)(body: (R1, R2, R3, R4) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2], arg2: Releasable[R3], arg3: Releasable[R4]): A

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.
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
A
the return type of the operation
resource1
the first resource
resource2
the second resource
resource3
the third resource
resource4
the fourth resource
body
the operation to perform using the resources
returns
the result of the operation, if neither the operation nor releasing the resources throws
def resources[R1, R2, R3, A](resource1: R1, resource2: ⇒ R2, resource3: ⇒ R3)(body: (R1, R2, R3) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2], arg2: Releasable[R3]): A

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.
R1
the type of the first resource
R2
the type of the second resource
R3
the type of the third resource
A
the return type of the operation
resource1
the first resource
resource2
the second resource
resource3
the third resource
body
the operation to perform using the resources
returns
the result of the operation, if neither the operation nor releasing the resources throws
def resources[R1, R2, A](resource1: R1, resource2: ⇒ R2)(body: (R1, R2) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2]): A

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.
R1
the type of the first resource
R2
the type of the second resource
A
the return type of the operation
resource1
the first resource
resource2
the second resource
body
the operation to perform using the resources
returns
the result of the operation, if neither the operation nor releasing the resources throws
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toString(): String

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Doc: package util

object Using

Usage

Suppression Behavior

Type Members

final class Manager extends AnyRef

trait Releasable[-R] extends AnyRef

Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

object Manager

object Releasable

def apply[R, A](resource: ⇒ R)(f: (R) ⇒ A)(implicit arg0: Releasable[R]): Try[A]

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

def resource[R, A](resource: R)(body: (R) ⇒ A)(implicit releasable: Releasable[R]): A

def resources[R1, R2, R3, R4, A](resource1: R1, resource2: ⇒ R2, resource3: ⇒ R3, resource4: ⇒ R4)(body: (R1, R2, R3, R4) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2], arg2: Releasable[R3], arg3: Releasable[R4]): A

def resources[R1, R2, R3, A](resource1: R1, resource2: ⇒ R2, resource3: ⇒ R3)(body: (R1, R2, R3) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2], arg2: Releasable[R3]): A

def resources[R1, R2, A](resource1: R1, resource2: ⇒ R2)(body: (R1, R2) ⇒ A)(implicit arg0: Releasable[R1], arg1: Releasable[R2]): A

final def synchronized[T0](arg0: ⇒ T0): T0

def toString(): String

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from AnyRef

Inherited from Any

Ungrouped