Functions

You can extend SpEL by registering user-defined functions that can be called within the expression string. The function is registered through the EvaluationContext. The following example shows how to register a user-defined function:

Java
Kotlin

Method method = ...;

EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();
context.setVariable("myFunction", method);

val method: Method = ...

val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()
context.setVariable("myFunction", method)

For example, consider the following utility method that reverses a string:

Java
Kotlin

public abstract class StringUtils {

	public static String reverseString(String input) {
		StringBuilder backwards = new StringBuilder(input.length());
		for (int i = 0; i < input.length(); i++) {
			backwards.append(input.charAt(input.length() - 1 - i));
		}
		return backwards.toString();
	}
}

fun reverseString(input: String): String {
	val backwards = StringBuilder(input.length)
	for (i in 0 until input.length) {
		backwards.append(input[input.length - 1 - i])
	}
	return backwards.toString()
}

You can then register and use the preceding method, as the following example shows:

Java
Kotlin

ExpressionParser parser = new SpelExpressionParser();

EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();
context.setVariable("reverseString",
		StringUtils.class.getDeclaredMethod("reverseString", String.class));

String helloWorldReversed = parser.parseExpression(
		"#reverseString('hello')").getValue(context, String.class);

val parser = SpelExpressionParser()

val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()
context.setVariable("reverseString", ::reverseString::javaMethod)

val helloWorldReversed = parser.parseExpression(
		"#reverseString('hello')").getValue(context, String::class.java)