用Java实现的一个轻量的条件表达式引擎。
原理无非就是利用递归与回溯算法解析表达式,再加上二叉树数据结构实现运算,以及栈数据结构实现优先级。
表达式引擎支持的运算符:
- 关系运算符:=,!=,>,>=,<,<=,in,is null,is not null
- 逻辑运算符:and ,or,not(逻辑与或非)
支持组合与优先级:
- not in可通过逻辑运算符not+关系运算符in实现
- is not null也可通过逻辑运算符not+关系运算符is null实现
- 支持(),优先级从左到右,()里面的优先,()与()之间,也是从左到右,符合正常数学层面理解的优先级
表达式书写要求:
- 字符串必要使用"'"开始,"'"结束
- in后面必须带括号
- and、or、not、in、is null、is not null左右两边至少要有一个空格
- and、or、not、in、is null、is not null不区分大小写
关系运算符简单使用:
a='jexpn'
a!='jexpn'
a>0
a>=0
a<1
a<=1
a in (1,2,3)
a in (1.0,2.0,3.0)
a in ('java','expr','engine')
a is null
a is not null
关系运算符与逻辑运算符混合使用:
a>0 and a<10
a<10 or a>100
not a=100
a>0 and not a=10
a>0 and a<100 and c=1 or d=0
加入优先级的复杂使用:
a='123' AND b!='123' OR (c='aa' AND d='ff')
(a>0 and a<10) or (b>10 or b<10) or not (c<0 and c>-100)
(a>0 and a<12) or (b>10 or b<10) or not (c<0 and c>-100)
(a>0 and a<10) or b=10 or not (c<0 and c>-100)
(a>0 and a<10) or (b>10 or b<10) or not (c<0 and c>-10)
使用方式:
/**
* @author wujiuye
*/
public class ExpressionParserTest {
public static void main(String[] args) {
// 解析表达式
Expression expr = ExpressionParser.fromString("(a>0 and a<10) or (b>10 or b<10) or not (c<0 and c>-100)");
// 设置变量值
Map<String,Object> bindings = new HashMap<>();
bindings.put("a", 11);
bindings.put("b", 10);
bindings.put("c", -10);
// 匹配
boolean triggered = expr.interpret(bindings);
System.out.println("匹配结果:" + triggered);
}
}
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