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前言

• 提取变量用正则也能做，但我看另一个项目用freemarker提取了模板的变量，就想着Velocity是不是也能做，搜了一圈没搜到，于是去debug了Velocity源码，发现变量最终会存在Node数组里。
  

实现代码

• 我只要能获取到Node [] children数组对象的数据就可以了。

import cn.hutool.core.util.StrUtil;
import cn.hutool.extra.template.Template;
import cn.hutool.extra.template.engine.velocity.VelocityEngine;
import cn.hutool.extra.template.engine.velocity.VelocityTemplate;
import com.zbkj.common.constants.Constants;
import org.apache.velocity.runtime.parser.node.ASTIdentifier;
import org.apache.velocity.runtime.parser.node.ASTReference;
import org.apache.velocity.runtime.parser.node.ASTprocess;
import org.apache.velocity.runtime.parser.node.Node;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;/*** @author zzq* @description Velocity工具类* @date 6/12/2025 14:12:44*/
public class VelocityUtil {private static final Logger log = LoggerFactory.getLogger(VelocityUtil.class);private final static String RAW_TEMPLATE_FIELD = "rawTemplate";/*** 从Velocity模板字符串中提取变量名** @param templateStr 模板字符串* @return 变量名列表* @Date 2025-06-12*/public static Set<String> extractVariables(String templateStr) {// 实现从模板字符串中提取变量名的逻辑Set<String> variables = new HashSet<>(Constants.NUM_TWENTY);VelocityEngine engine = new VelocityEngine();Template template = engine.getTemplate(templateStr);Field rawTemplateField = ReflectionUtils.findField(VelocityTemplate.class, RAW_TEMPLATE_FIELD);ReflectionUtils.makeAccessible(rawTemplateField);org.apache.velocity.Template rawTemplate = (org.apache.velocity.Template) ReflectionUtils.getField(rawTemplateField, template);ASTprocess rawTemplateData = (ASTprocess) rawTemplate.getData();if (!ObjectUtils.isEmpty(rawTemplateData)) {int nodeLength = rawTemplateData.jjtGetNumChildren();for (int i = 0; i < nodeLength; i++) {StringBuilder sb = new StringBuilder();// 第一级节点Node child = rawTemplateData.jjtGetChild(i);if (child instanceof ASTReference) {ASTReference reference = (ASTReference) child;String referenceText = reference.getRootString();sb.append(referenceText);
//                    log.info("Reference: " + referenceText);int nodeGrandLen = reference.jjtGetNumChildren();// 子孙节点for (int j = 0; j < nodeGrandLen; j++) {Node grandChild = reference.jjtGetChild(j);if (grandChild instanceof ASTIdentifier) {ASTIdentifier identifier = (ASTIdentifier) grandChild;sb.append(StrUtil.DOT + identifier.getIdentifier());
//                            log.info("Identifier: " + identifier.getIdentifier());}}variables.add(sb.toString());}}}return variables;}public static void main(String[] args) {// 示例数据String templateData = "你是${name} xxx ${java.lang.String.XTEST} ${java.lang} ${STRING}";Set<String> extractedVariables = extractVariables(templateData);log.info("Extracted Variables: " + extractedVariables);}
}

• 运行效果
  

• 本身项目是Spring Boot，其他程序依赖

<dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>4.5.7</version>
</dependency><!-- velocity代码生成使用模板 -->
<dependency><groupId>org.apache.velocity</groupId><artifactId>velocity-engine-core</artifactId><version>2.3</version>
</dependency>