Object scala.util.control.Exception

object Exception

Classes representing the components of exception handling.

Each class is independently composable.

This class differs from scala.util.Try in that it focuses on composing exception handlers rather than composing behavior. All behavior should be composed first and fed to a Catch object using one of the opt, either or withTry methods. Taken together the classes provide a DSL for composing catch and finally behaviors.

Examples

Create a Catch which handles specified exceptions.

import scala.util.control.Exception._
import java.net._

val s = "http://www.scala-lang.org/"

// Some(http://www.scala-lang.org/)
val x1: Option[URL] = catching(classOf[MalformedURLException]) opt new URL(s)

// Right(http://www.scala-lang.org/)
val x2: Either[Throwable,URL] =
  catching(classOf[MalformedURLException], classOf[NullPointerException]) either new URL(s)

// Success(http://www.scala-lang.org/)
val x3: Try[URL] = catching(classOf[MalformedURLException], classOf[NullPointerException]) withTry new URL(s)

val defaultUrl = new URL("http://example.com")
//  URL(http://example.com) because htt/xx throws MalformedURLException
val x4: URL = failAsValue(classOf[MalformedURLException])(defaultUrl)(new URL("htt/xx"))

Create a Catch which logs exceptions using handling and by.

def log(t: Throwable): Unit = t.printStackTrace

val withThrowableLogging: Catch[Unit] = handling(classOf[MalformedURLException]) by (log)

def printUrl(url: String) : Unit = {
  val con = new URL(url) openConnection()
  val source = scala.io.Source.fromInputStream(con.getInputStream())
  source.getLines.foreach(println)
}

val badUrl = "htt/xx"
// Prints stacktrace,
//   java.net.MalformedURLException: no protocol: htt/xx
//     at java.net.URL.<init>(URL.java:586)
withThrowableLogging { printUrl(badUrl) }

val goodUrl = "http://www.scala-lang.org/"
// Prints page content,
//   <!DOCTYPE html>
//   <html>
withThrowableLogging { printUrl(goodUrl) }

Use unwrapping to create a Catch that unwraps exceptions before rethrowing.

class AppException(cause: Throwable) extends RuntimeException(cause)

val unwrappingCatch: Catch[Nothing] = unwrapping(classOf[AppException])

def calcResult: Int = throw new AppException(new NullPointerException)

// Throws NPE not AppException,
//   java.lang.NullPointerException
//     at .calcResult(<console>:17)
val result = unwrappingCatch(calcResult)

Use failAsValue to provide a default when a specified exception is caught.

val inputDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0)
val candidatePick = "seven" // scala.io.StdIn.readLine()

// Int = 0
val pick = inputDefaulting(candidatePick.toInt)

Compose multiple Catchs with or to build a Catch that provides default values varied by exception.

val formatDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0)
val nullDefaulting: Catch[Int] = failAsValue(classOf[NullPointerException])(-1)
val otherDefaulting: Catch[Int] = nonFatalCatch withApply(_ => -100)

val combinedDefaulting: Catch[Int] = formatDefaulting or nullDefaulting or otherDefaulting

def p(s: String): Int = s.length * s.toInt

// Int = 0
combinedDefaulting(p("tenty-nine"))

// Int = -1
combinedDefaulting(p(null: String))

// Int = -100
combinedDefaulting(throw new IllegalStateException)

// Int = 22
combinedDefaulting(p("11"))
Source
Exception.scala
Linear Supertypes

Type Members

class By[T, R] extends AnyRef

class Catch[+T] extends Described

A container class for catch/finally logic.

Pass a different value for rethrow if you want to probably unwisely allow catching control exceptions and other throwables which the rest of the world may expect to get through.

T

result type of bodies used in try and catch blocks

type Catcher[+T] = PartialFunction[Throwable, T]

trait Described extends AnyRef

class Finally extends Described

Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(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

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def allCatch[T]: Catch[T]

final def allCatcher[T]: Catcher[T]

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

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def catching[T](c: Catcher[T]): Catch[T]

def catching[T](exceptions: Class[_]*): Catch[T]

Creates a Catch object which will catch any of the supplied exceptions. Since the returned Catch object has no specific logic defined and will simply rethrow the exceptions it catches, you will typically want to call opt, either or withTry on the return value, or assign custom logic by calling "withApply".

Note that Catch objects automatically rethrow ControlExceptions and others which should only be caught in exceptional circumstances. If you really want to catch exactly what you specify, use catchingPromiscuously instead.

def catchingPromiscuously[T](c: Catcher[T]): Catch[T]

def catchingPromiscuously[T](exceptions: Class[_]*): Catch[T]

Creates a Catch object which will catch any of the supplied exceptions. Unlike "catching" which filters out those in shouldRethrow, this one will catch whatever you ask of it including ControlThrowable or InterruptedException .

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.

Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws( ... ) @native()
Note

not specified by SLS as a member of AnyRef

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

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(arg0: Any): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

def failAsValue[T](exceptions: Class[_]*)(value: ⇒ T): Catch[T]

def failing[T](exceptions: Class[_]*): Catch[Option[T]]

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.

Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
Note

not specified by SLS as a member of AnyRef

final def getClass(): Class[_]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def handling[T](exceptions: Class[_]*): By[(Throwable) ⇒ T, Catch[T]]

Returns a partially constructed Catch object, which you must give an exception handler function as an argument to by.

Example:
    handling(classOf[MalformedURLException], classOf[NullPointerException]) by (_.printStackTrace)

def hashCode(): Int

The hashCode method for reference types. See hashCode in scala.Any.

returns

the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()

def ignoring(exceptions: Class[_]*): Catch[Unit]

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

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

def mkCatcher[Ex <: Throwable, T](isDef: (Ex) ⇒ Boolean, f: (Ex) ⇒ T)(implicit arg0: ClassTag[Ex]): Catcher[T]

def mkThrowableCatcher[T](isDef: (Throwable) ⇒ Boolean, f: (Throwable) ⇒ T): Catcher[T]

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

final val noCatch: Catch[Nothing]

final def nonFatalCatch[T]: Catch[T]

final def nonFatalCatcher[T]: Catcher[T]

final val nothingCatcher: Catcher[Nothing]

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 shouldRethrow(x: Throwable): Boolean

!!! Not at all sure of every factor which goes into this, and/or whether we need multiple standard variations.

returns

true if x is ControlThrowable or InterruptedException otherwise false.

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

Definition Classes
AnyRef

implicit def throwableSubtypeToCatcher[Ex <: Throwable, T](pf: PartialFunction[Ex, T])(implicit arg0: ClassTag[Ex]): Catcher[T]

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

def ultimately[T](body: ⇒ Unit): Catch[T]

def unwrapping[T](exceptions: Class[_]*): Catch[T]

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( ... ) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/util/control/Exception$.html