Properties, Arrays, Lists, Maps, and Indexers

Navigating with property references is easy. To do so, use a period to indicate a nested property value. The instances of the Inventor class, pupin and tesla, were populated with data listed in the Classes used in the examples section. To navigate "down" the object graph and get Tesla’s year of birth and Pupin’s city of birth, we use the following expressions:

Java
Kotlin

// evaluates to 1856
int year = (Integer) parser.parseExpression("birthdate.year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.city").getValue(context);

// evaluates to 1856
val year = parser.parseExpression("birthdate.year + 1900").getValue(context) as Int

val city = parser.parseExpression("placeOfBirth.city").getValue(context) as String

Case insensitivity is allowed for the first letter of property names. Thus, the expressions in the above example may be written as Birthdate.Year + 1900 and PlaceOfBirth.City, respectively. In addition, properties may optionally be accessed via method invocations — for example, getPlaceOfBirth().getCity() instead of placeOfBirth.city.

The contents of arrays and lists are obtained by using square bracket notation, as the following example shows:

Java
Kotlin

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

// Inventions Array

// evaluates to "Induction motor"
String invention = parser.parseExpression("inventions[3]").getValue(
		context, tesla, String.class);

// Members List

// evaluates to "Nikola Tesla"
String name = parser.parseExpression("members[0].name").getValue(
		context, ieee, String.class);

// List and Array navigation
// evaluates to "Wireless communication"
String invention = parser.parseExpression("members[0].inventions[6]").getValue(
		context, ieee, String.class);

val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

// Inventions Array

// evaluates to "Induction motor"
val invention = parser.parseExpression("inventions[3]").getValue(
		context, tesla, String::class.java)

// Members List

// evaluates to "Nikola Tesla"
val name = parser.parseExpression("members[0].name").getValue(
		context, ieee, String::class.java)

// List and Array navigation
// evaluates to "Wireless communication"
val invention = parser.parseExpression("members[0].inventions[6]").getValue(
		context, ieee, String::class.java)

The contents of maps are obtained by specifying the literal key value within the brackets. In the following example, because keys for the officers map are strings, we can specify string literals:

Java
Kotlin

// Officer's Dictionary

Inventor pupin = parser.parseExpression("officers['president']").getValue(
		societyContext, Inventor.class);

// evaluates to "Idvor"
String city = parser.parseExpression("officers['president'].placeOfBirth.city").getValue(
		societyContext, String.class);

// setting values
parser.parseExpression("officers['advisors'][0].placeOfBirth.country").setValue(
		societyContext, "Croatia");

// Officer's Dictionary

val pupin = parser.parseExpression("officers['president']").getValue(
		societyContext, Inventor::class.java)

// evaluates to "Idvor"
val city = parser.parseExpression("officers['president'].placeOfBirth.city").getValue(
		societyContext, String::class.java)

// setting values
parser.parseExpression("officers['advisors'][0].placeOfBirth.country").setValue(
		societyContext, "Croatia")