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对于最新的稳定版本，请使用 Spring Framework 7.0.6! |
功能
您可以通过注册用户定义的函数来扩展SpEL，这些函数可以在表达式字符串中调用。该函数通过EvaluationContext进行注册。以下示例显示了如何注册用户定义的函数：
-
Java
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Kotlin
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，考虑以下将字符串反转的实用方法：
-
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()
}然后可以注册并使用前面的方法，如下例所示：
-
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)