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.
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)
}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.
the type of the resource
Test two objects for inequality.
true if !(this == that), false otherwise.
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.
a hash value consistent with ==
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
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.
a Try containing an exception if one or more were thrown, or the result of the operation if no exceptions were thrown
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.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
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:
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).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
true if the receiver object is equivalent to the argument; false otherwise.
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.
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
The hashCode method for reference types. See hashCode in scala.Any.
the hash code value for this object.
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.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
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.
the type of the resource
the return type of the operation
the resource
the operation to perform with the resource
the result of the operation, if neither the operation nor releasing the resource throws
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.
the type of the first resource
the type of the second resource
the type of the third resource
the type of the fourth resource
the return type of the operation
the first resource
the second resource
the third resource
the fourth resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
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.
the type of the first resource
the type of the second resource
the type of the third resource
the return type of the operation
the first resource
the second resource
the third resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
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.
the type of the first resource
the type of the second resource
the return type of the operation
the first resource
the second resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
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.
a String representation of the object.
© 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.