jexl表达式解析、计算工具类.md

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jexl表达式解析、计算工具类.md 根据表达式可以动态反向解析出变量；适合动态表达式，参数未知场景 如 （A0.2+B0.8）/C 解析出 A\B\C，把ABC参数值代入计算 初始化引擎

private static final JexlEngine ENGINE = new JexlEngine();
static {
    ENGINE.setCache(512);
    ENGINE.setLenient(false);
    ENGINE.setSilent(false);
}

解析出表达式中的变量 ExpressionUtils

package com.its.cloud.utils;
 
import com.google.common.base.Joiner;
import com.google.common.collect.Lists;
 
import org.apache.commons.jexl2.Expression;
import org.apache.commons.jexl2.ExpressionImpl;
import org.apache.commons.jexl2.JexlEngine;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
import java.util.Collections;
import java.util.List;
import java.util.Set;
 
/**
* Created by [email protected] on 2015/1/19.
*/
public class ExpressionUtils {
 
    private static final Logger LOGGER = LoggerFactory.getLogger(ExpressionUtils.class);
    private static final JexlEngine JEXL = new JexlEngine();
 
    static {
        JEXL.setCache(512);
        JEXL.setLenient(false);
        JEXL.setSilent(false);
    }
 
    public static JexlEngine getJexlEngine() {
        return JEXL;
    }
 
    public static boolean isValidExpression(String expression) {
        try {
            JEXL.createExpression(expression);
            return true;
        } catch (Throwable t) {
            LOGGER.error("表达式{}配置错误{}。", expression, t.getMessage(), t);
            return false;
        }
    }
 
    /**
     * 获取表达式中的变量参数
     *
     * @param expression 表达式，如 ping.max>0 and ping.min>0 and pin.lost==0
     */
    public static List getVariables(String expression) {
        Expression exp;
        try {
            exp = JEXL.createExpression(expression);
        } catch (Throwable t) {
            LOGGER.error("表达式{}配置错误{}。", expression, t.getMessage(), t);
            return Collections.emptyList();
        }
        return getVariables(exp);
    }
 
    public static List getVariables(Expression exp) {
        List metricDefIds = Lists.newArrayList();
        Set> variables = JEXL.getVariables((ExpressionImpl) exp);
        for (List var : variables) {
            metricDefIds.add(Joiner.on(".").join(var));
        }
        return metricDefIds;
    }
}

解析变量，调用示例

jexl反向解析表达式中的变量
JexlEngine jexl = new JexlEngine();
String threshold = "(value==3)and (cpu>90 and mem <70)";
Expression exp = jexl.createExpression(threshold);

List variables = jexl.getVariables(((ExpressionImpl)exp));

表达式示例

String threshold = "value>90";
        Expression exp = getJexlEngine().createExpression(threshold);
        JexlContext jc = new MapContext();
        jc.set("value", data.getValue());
        Object evaluate = exp.evaluate(jc);
        if (evaluate instanceof Boolean) {
            return (boolean) evaluate;
        } else {
            LOGGER.error("表达式错误{}，不是boolean返回值;{}", exp, rule);
            return false;
        }

转载于:https://my.oschina.net/itnms/blog/465742