Object scala.util.Using
object Using
Type Members
final class Manager extends AnyRef
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
Managerfor the creation of custom resources, and to callacquireduring 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 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
Test two objects for inequality.
- returns
trueif !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
final def ##(): Int
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
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.
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
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastExceptionif the receiver object is not an instance of the erasure of typeT0.
def clone(): AnyRef
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
- returns
a copy of the receiver object.
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
-
It is consistent: for any non-null instances
x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
null.eq(null) returns true. When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
- returns
trueif the argument is a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
def equals(arg0: AnyRef): Boolean
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.
final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- returns
a class object corresponding to the runtime type of the receiver.
def hashCode(): Int
The hashCode method for reference types. See hashCode in scala.Any.
- returns
the hash code value for this object.
final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
- returns
trueif the receiver object is an instance of erasure of typeT0;falseotherwise.
- Definition Classes
- Any
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
- returns
trueif the argument is not a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of 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. 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. 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. 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. 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
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
- returns
a String representation of the object.
- Definition Classes
- AnyRef → Any
final def wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long): Unit
object Manager
object Releasable
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/util/Using$.html
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, theapplymethod is easiest; it wraps the resource opening, operation, and resource releasing in aTry.Example:
val lines: Try[Seq[String]] = Using(new BufferedReader(new FileReader("file.txt"))) { reader => Iterator.unfold(())(_ => Option(reader.readLine()).map(_ -> ())).toList }If you need to manage multiple resources,
Using.Managershould be used. It allows the managing of arbitrarily many resources, whose creation, use, and release are all wrapped in aTry.Example:
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.unfold(())(_ => Option(reader.readLine()).map(_ -> ())) (lines(r1) ++ lines(r2) ++ lines(r3) ++ lines(r4)).toList }If you wish to avoid wrapping management and operations in a
Try, you can useUsing.resource, which throws any exceptions that occur.Example:
val lines: Seq[String] = Using.resource(new BufferedReader(new FileReader("file.txt"))) { reader => Iterator.unfold(())(_ => Option(reader.readLine()).map(_ -> ())).toList }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 anenableSuppressionparameter), an exception that would have been suppressed is instead discarded.Exceptions are ranked from highest to lowest severity as follows:
java.lang.VirtualMachineErrorjava.lang.LinkageErrorjava.lang.InterruptedExceptionandjava.lang.ThreadDeathscala.util.control.ControlThrowablescala.util.control.ControlThrowableWhen 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.