Safe Navigation Operator

The safe navigation operator is used to avoid a NullPointerException and comes from the Groovy language. Typically, when you have a reference to an object, you might need to verify that it is not null before accessing methods or properties of the object. To avoid this, the safe navigation operator returns null instead of throwing an exception. The following example shows how to use the safe navigation operator:

  • Java

  • Kotlin

ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
tesla.setPlaceOfBirth(new PlaceOfBirth("Smiljan"));

String city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String.class);
System.out.println(city);  // Smiljan

tesla.setPlaceOfBirth(null);
city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String.class);
System.out.println(city);  // null - does not throw NullPointerException!!!
val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

val tesla = Inventor("Nikola Tesla", "Serbian")
tesla.setPlaceOfBirth(PlaceOfBirth("Smiljan"))

var city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String::class.java)
println(city)  // Smiljan

tesla.setPlaceOfBirth(null)
city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String::class.java)
println(city)  // null - does not throw NullPointerException!!!