How to verify if an object has certain property?

I want to use either a value of expected property or a specified default. How to achieve this in groovy?

Let's look at the example:

def printName(object) {
   //if object has initialized property 'name' - print 'name', otherwise print ToString
   if (object<some code here>name && object.name) {
      print object.name
   } else {
      print object
   }
}

You can use hasProperty. Example:

if (object.hasProperty('name') && object.name) {
    println object.name
} else {
    println object
}

If you're using a variable for the property name, you can use this:

String propName = 'name'
if (object.hasProperty(propName) && object."$propName") {
    ...
}

Assuming your object is a Groovy class, you can use hasProperty in the object metaClass like so:

def printName( o ) {
  if( o.metaClass.hasProperty( o, 'name' ) && o.name ) {
    println "Printing Name : $o.name"
  }
  else {
    println o
  }
}

So, then given two classes:

class Named {
  String name
  int age
  
  String toString() { "toString Named:$name/$age" }
}

class Unnamed {
  int age

  String toString() { "toString Unnamed:$age" }
}

You can create instance of them, and test:

def a = new Named( name: 'tim', age: 21 )
def b = new Unnamed( age: 32 )

printName( a )
printName( b )

Which should output:

Printing Name : tim
toString Unnamed:32

You can write your own method via meta-programming:

class Foo {
    def name = "Mozart"
}

def f = new Foo()

Object.metaClass.getPropertyOrElse = { prop, defaultVal ->
    delegate.hasProperty(prop) ? delegate."${prop}" : defaultVal
}

assert "Mozart" == f.getPropertyOrElse("name", "")
assert "Salzburg" == f.getPropertyOrElse("city", "Salzburg")

If I simply want to assert that an object has some property, I just test the following:

assertNotNull(myObject.hasProperty('myProperty').name)

If myObject does not have myProperty the assertion will fail with a null pointer exception:

java.lang.NullPointerException: Cannot get property 'name' on null object