对于最新稳定版本，请使用 Spring Framework 7.0.6！spring-doc.cadn.net.cn

函数

你可以通过注册用户自定义函数来扩展 SpEL，这些函数可以在表达式字符串中被调用。该函数通过 EvaluationContext 进行注册。以下示例展示了如何注册一个用户自定义函数：spring-doc.cadn.net.cn

Method method = ...;

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

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

例如，考虑以下用于反转字符串的工具方法：spring-doc.cadn.net.cn

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()
}

然后，您可以注册并使用上述方法，如下例所示：spring-doc.cadn.net.cn

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)