Check if a string is blank or doesn't exist in Scala

Question

I have an Option[String].

I want to check if there is a string exists and if it's exists its not blank.

def isBlank( input : Option[String]) : Boolean = 
{ 
     input.isEmpty || 
     input.filter(_.trim.length > 0).isEmpty 
}

Is there is a better way of doing this in Scala ?

Answer 1

What you should do is check using exists. Like so:

myOption.exists(_.trim.nonEmpty)

which will return True if and only if the Option[String] is not None and not empty.

Answer 2

An approach based in pattern matching,

def isBlank( input : Option[String]) : Boolean = 
  input match {
    case None    => true
    case Some(s) => s.trim.isEmpty
  }

Answer 3

This should work as well since filter of an empty Option results in an empty Option

def isBlank( input : Option[String]) : Boolean =  
   input.filter(_.trim.length > 0).isEmpty 

Answer 4

All proposed solutions will crash with NullPointerException if you pass:

val str : Option[String] = Some(null). 

Therefore null-check is a must:

def isBlank(input: Option[String]): Boolean = 
  input.filterNot(s => s == null || s.trim.isEmpty).isEmpty

Answer 5

exists (Accepted solution) will work when input has at least one element in it, that is Some("") but not when it's None.

exists checks if at least one element(x) applies to function.

eg.

scala> List[String]("apple", "").exists(_.isEmpty)
res21: Boolean = true

//if theres no element then obviously returns false
scala> List[String]().exists(_.isEmpty)
res30: Boolean = false

Same happens with Option.empty, as theres no element in it,

scala> Option.empty[String].exists(_.isEmpty)
res33: Boolean = false

So forall is what makes sure the the function applies all the elements.

scala> def isEmpty(sOpt: Option[String]) = sOpt.forall(_.trim.isEmpty)
isEmpty: (sOpt: Option[String])Boolean

scala> isEmpty(Some(""))
res10: Boolean = true

scala> isEmpty(Some("non-empty"))
res11: Boolean = false

scala> isEmpty(Option(null))
res12: Boolean = true

The gross way is to filter nonEmpty string, then check option.isEmpty.

scala> def isEmpty(sOpt: Option[String]) = sOpt.filter(_.trim.nonEmpty).isEmpty
isEmpty: (sOpt: Option[String])Boolean

scala> isEmpty(None)
res20: Boolean = true

scala> isEmpty(Some(""))
res21: Boolean = true

Answer 6

I am from C# background and found Scala implicit methods similar to C# extensions

import com.foo.bar.utils.MyExtensions._
...

"my string".isNullOrEmpty  // false
"".isNullOrEmpty           // true
" ".isNullOrEmpty          // true
"  ".isNullOrEmpty         // true

val str: String  = null
str.isNullOrEmpty          // true

Implementation

package com.foo.bar.utils

object MyExtensions {

  class StringEx(val input: String) extends AnyVal {

    def isNullOrEmpty: Boolean =    
      if (input == null || input.trim.isEmpty)
        true
      else
        false
  }

  implicit def isNullOrEmpty(input: String): StringEx = new StringEx(input)
}

Answer 7

You can also take advantage of Extractor pattern. It makes codes much more declarative.

For example:

object NonBlank {
  def unapply(s: String): Option[String] = Option(s).filter(_.trim.nonEmpty) 
}

And then use it like

def createUser(name: String): Either[Error, User] = name match {
  case NonBlank(username) => Right(userService.create(username))
  case _ => Left(new Error("Invalid username. Blank usernames are not allowed."))
}

Answer 8

I added a Scalafiddle to play with that: Scalafiddle

That shows the marked correct answer is wrong (as pointed out by prayagupd):

def isBlank(str: Option[String]): Boolean =
   str.forall(_.trim.isEmpty)

the solution is for non-blank:

def isNotBlank(str: Option[String]): Boolean =
   str.exists(_.trim.nonEmpty)