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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.(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
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Type Members

  1. class By [T, R] extends AnyRef
  2. class Catch [+T] extends Described

    A container class for catch/finally logic.

    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

  3. type Catcher[+T] = PartialFunction[Throwable, T]
  4. trait Described extends AnyRef
  5. class Finally extends Described

    A container class for finally code.

Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

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

    Equivalent to x.hashCode except for boxed numeric types and null.

    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
  3. final def ==(arg0: Any): Boolean

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    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
  4. final def allCatch[T]: Catch[T]

    A Catch object which catches everything.

  5. final def allCatcher[T]: Catcher[T]
  6. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type 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.

  7. def catching[T](c: Catcher[T]): Catch[T]
  8. def catching[T](exceptions: Class[_]*): Catch[T]

    Creates a Catch object which will catch any of the supplied exceptions.

    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.

  9. def catchingPromiscuously[T](c: Catcher[T]): Catch[T]
  10. def catchingPromiscuously[T](exceptions: Class[_]*): Catch[T]

    Creates a Catch object which will catch any of the supplied exceptions.

    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 .

  11. def clone(): AnyRef

    Create a copy of the receiver object.

    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[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
    Note

    not specified by SLS as a member of AnyRef

  12. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (that) is a reference to the receiver object (this).

    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
  13. def equals(arg0: Any): Boolean

    The equality method for reference types.

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

    Creates a Catch object which maps all the supplied exceptions to the given value.

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

    Creates a Catch object which maps all the supplied exceptions to None.

  16. def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

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

    not specified by SLS as a member of AnyRef

  17. final def getClass(): Class[_]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

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

    Definition Classes
    AnyRef → Any
  18. 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.

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

    Example: 

    1. handling(classOf[MalformedURLException], classOf[NullPointerException]) by (_.printStackTrace)
  19. def hashCode(): Int

    The hashCode method for reference types.

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

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
  20. def ignoring(exceptions: Class[_]*): Catch[Unit]

    Creates a Catch object which catches and ignores any of the supplied exceptions.

  21. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    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
  22. def mkCatcher[Ex <: Throwable, T](isDef: (Ex) ⇒ Boolean, f: (Ex) ⇒ T)(implicit arg0: ClassTag[Ex]): Catcher[T]
  23. def mkThrowableCatcher[T](isDef: (Throwable) ⇒ Boolean, f: (Throwable) ⇒ T): Catcher[T]
  24. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

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

    Definition Classes
    AnyRef
  25. final val noCatch: Catch[Nothing]

    The empty Catch object.

  26. final def nonFatalCatch[T]: Catch[T]

    A Catch object which catches non-fatal exceptions.

  27. final def nonFatalCatcher[T]: Catcher[T]
  28. final val nothingCatcher: Catcher[Nothing]
  29. final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  30. final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  31. def shouldRethrow(x: Throwable): Boolean

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

    !!! 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.

  32. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  33. implicit def throwableSubtypeToCatcher[Ex <: Throwable, T](pf: PartialFunction[Ex, T])(implicit arg0: ClassTag[Ex]): Catcher[T]
  34. def toString(): String

    Creates a String representation of this object.

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

    Returns a Catch object with no catch logic and the argument as the finally logic.

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

    Creates a Catch object which unwraps any of the supplied exceptions.

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

Inherited from AnyRef

Inherited from Any

Catch behavior composition

Build Catch objects from exception lists and catch logic

Finally behavior composition

Build Catch objects from finally logic

General purpose catch objects

Catch objects with predefined behavior. Use combinator methods to compose additional behavior.

DSL behavior composition

Expressive Catch behavior composition

Promiscuous Catch behaviors

Useful if catching ControlThrowable or InterruptedException is required.

Logic Containers

Containers for catch and finally behavior.

Ungrouped