Scala Spring @Value in constructor body

Question

I have the following spring pseudo-code wired scala class.

@Service
class Something {

@Value("${some.property}")
val someString : String

// do something with someString in the body
}

However this won't work because the someString is part of the constructor body, and spring can't wire in the values until after the constructor has executed.

How can I wire in @Value's so that it works, and isn't horrible (my current solution with a custom constructor containing all the values I need just doesn't feel "scala" and looks horrible.

Edit: To clarify, my current solution is this:

@Service
class Something { 
  @Autowired 
  def this(@Value("${some.prop}") prop : String) { 
    this() 
    // do other construction stuff here
  }
}

I just think it looks ugly and feel there is a better way. I also don't like having to create these secondary constructors when I'd rather enforce it on the primary constructor.

Edit 2: To further clarify, I was hoping there was a way to do something like this:

@Service
class Something(@Value("${some.property}") string : String) {
// use the value in your constructor here
}

Because this looks far more elegant. I just can't get it to work :)

Answer 1

Ok, after all the back and forth, I think I understand better what you want, so here's my take on it:

import scala.annotation.BeanProperty
import scala.annotation.target.beanSetter
class Something @Autowired() (@(Value @beanSetter)("{some.property}") @BeanProperty var prop: String)

This is essentially Paolo Falabella's solution, except that I try to avoid having Spring acces private fields. To this end I let scala autogenerate a public java-like setter using @BeanProperty and apply @Value on it. You can also improve the syntax somewhat by using a type alias:

type Value = org.springframework.beans.factory.annotation.Value @beanSetter @beanGetter
class Something @Autowired() ( @BeanProperty@Value("{some.property}") var prop: String)

Answer 2

You need to initialize someString to a value so that a real field is generated in the class. Alternatively you can use a var instead of a val, but either way you'll have to initialize it.

For example:

@Service
class TestService {
  @Value("${testService.foo:bar}")
  val foo: String = null
  //var foo: String = _
}

Decompiling TestService.class file you'll see that it put the annotation on a private final String field (you can also use jclasslib bytecode viewer):

@Service
@ScalaSignature(bytes="\006\001!3A!\001\002\001\023\tYA+Z:u'\026\024h/[2f\025\t\031A!\001\005tKJ4\030nY3t\025\t)a!A\002osbT\021aB\001\004G>l7\001A\n\004\001)\021\002CA\006\021\033\005a!BA\007\017\003\021a\027M\\4\013\003=\tAA[1wC&\021\021\003\004\002\007\037\nTWm\031;\021\005M1R\"\001\013\013\003U\tQa]2bY\006L!a\006\013\003\027M\033\027\r\\1PE*,7\r\036\005\0063\001!\tAG\001\007y%t\027\016\036 \025\003m\001\"\001\b\001\016\003\tAqA\b\001C\002\023\005q$A\002g_>,\022\001\t\t\003C\021r!a\005\022\n\005\r\"\022A\002)sK\022,g-\003\002&M\t11\013\036:j]\036T!a\t\013\t\r!\002\001\025!\003!\003\0211wn\034\021)\t\035R\003(\017\t\003WYj\021\001\f\006\003[9\n!\"\0318o_R\fG/[8o\025\ty\003'A\004gC\016$xN]=\013\005E\022\024!\0022fC:\034(BA\0325\003=\031\bO]5oO\032\024\030-\\3x_J\\'\"A\033\002\007=\024x-\003\0028Y\t)a+\0317vK\006)a/\0317vK\006\n!(\001\f%wR,7\017^*feZL7-\032\030g_>T$-\031:~\021\025a\004\001\"\001>\003)Ig.\033;jC2L'0\032\013\002}A\0211cP\005\003\001R\021A!\0268ji\"\022\001A\021\t\003\007\032k\021\001\022\006\003\013J\n!b\035;fe\026|G/\0379f\023\t9EIA\004TKJ4\030nY3")
public class TestService
  implements ScalaObject
{

  @Value("${testService.foo:bar}")
  private final String foo;

  public String foo()
  {
    return this.foo;
  }

  public TestService()
  {
    null; this.foo = null;
  }
}

I use @Value on class members all the time, it's very convenient.