使用Groovy自定义解析表达式

一、引入Groovy依赖

<dependency>
    <groupId>org.codehaus.groovygroupId>
    <artifactId>groovy-allartifactId>
    <version>2.4.7version>
dependency>

二、自定义脚本

package com.epf.activiti.utils;
import groovy.lang.Script;

import java.lang.reflect.Method;

/**
 * 自定义脚本
 * @author   GZEPF
 * @date     2018 2018年8月28日 下午7:56:15
 */
public class ExprBasicScript extends Script  {

    @Override
    public Object run() {
        //show usage
        Method[] methods = ExprBasicScript.class.getDeclaredMethods();
        StringBuilder sb=new StringBuilder();
        for (Method method : methods) {
            sb.append(method);
        }

        return sb.substring(0, sb.length()-1);
    }

    public static Object nvl(Object str, Object val) {
        return str == null || "".equals(str) ? val : str;
    }

}

三、读取解析表达式

package com.epf.activiti.utils;
import groovy.lang.Binding;
import groovy.lang.GroovyShell;
import groovy.lang.Script;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;

import org.codehaus.groovy.control.CompilerConfiguration;

public class ExprSupportUtils {

    private static final Object lock = new Object();
    private static final GroovyShell shell;

    private static Hashtable cache = new Hashtable();
    static {
        CompilerConfiguration cfg = new CompilerConfiguration();
        cfg.setScriptBaseClass(MyBasicScript.class.getName());

        shell = new GroovyShell(cfg);
    }

    public static Object parseExpr(String expr) {
        Script s = getScriptFromCache(expr);
        return s.run();
    }

    public static Object parseExpr(String expr, Map map) {
        Binding binding = new Binding(map);
        Script script = getScriptFromCache(expr);
        script.setBinding(binding);
        return script.run();
    }

    private static Script getScriptFromCache(String expr) {
        if (cache.contains(expr)) {
            return cache.get(expr);
        }
        synchronized (lock) {
            if (cache.contains(expr)) {
                return cache.get(expr);
            }
            Script script = shell.parse(expr);
            cache.put(expr, script);
            return script;
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {

        // eg. get one row from db
        Map row = new HashMap();
        row.put("id", 42);
        row.put("name", "");

        //带绑定数据参数的调用方式
        System.out.println(ExprSupportUtils.parseExpr("nvl(id,0)", row));
        System.out.println(ExprSupportUtils.parseExpr("nvl(name,'anonymous')", row));
         //${user.depart}  == 'divitPerson'
        //不带绑定数据参数的调用方式，这个是groovy的内置能力
         Map map = new HashMap<>();
         map.put("depart", "divitPerson");
         map.put("dayTime", 1);
        System.out.println(ExprSupportUtils.parseExpr("depart.contains('divitPerson') && dayTime > 0  ",map));

    }

}

参考地址
- Drools, IKExpression, Aviator和Groovy字符串表达式求值比较
- Java中使用Groovy实现自定义表达式解析