使用Groovy自定义解析表达式

ゞ浴缸里的玫瑰 2022-05-14 20:17 221阅读 0赞

#### 一、引入Groovy依赖 ####

<dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-all</artifactId>
        <version>2.4.7</version>
    </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<String, Script> cache = new Hashtable<String, Script>();
        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<String, Object> row = new HashMap<String, Object>();
            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<String, Object> 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][Drools_ IKExpression_ Aviator_Groovy]  
> \- [Java中使用Groovy实现自定义表达式解析][Java_Groovy]

[Drools_ IKExpression_ Aviator_Groovy]: https://blog.csdn.net/xch_w/article/details/7865620
[Java_Groovy]: https://www.cnblogs.com/ora11g/p/4473544.html