如何在手动Spring表达式语言评估过程中使用属性引用${key:default}

import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.util.PropertyPlaceholderHelper;

public class Main {
    public static void main(String[] args) {
        // 创建属性解析器
        ExpressionParser parser = new SpelExpressionParser();
        
        // 属性字符串
        String expressionString = "Hello ${name:World}!";
        
        // 创建属性占位符助手
        PropertyPlaceholderHelper helper = new PropertyPlaceholderHelper("${", "}");
        
        // 解析属性
        String resolvedString = helper.replacePlaceholders(expressionString, new PropertyPlaceholderResolver());
        
        // 使用Spring表达式语言进行属性引用
        Expression expression = parser.parseExpression(resolvedString);
        String result = expression.getValue(String.class);
        
        System.out.println(result);  // 输出：Hello Alice!
    }
    
    static class PropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {
        @Override
        public String resolvePlaceholder(String placeholderName) {
            // 返回属性值
            if (placeholderName.equals("name")) {
                return "Alice";
            }
            return null;
        }
    }
}