java 使用JEP解析字符串计算公式求值(附带自定义函数编写)

矫情吗；* 2023-05-22 10:30 11阅读 0赞

2.X 存在精确度问题 推荐使用3.X 参考文章: [java 使用 jep3.5 解析公式自动计算(包含BigDecimal模式 浮点数精准计算)][java _ jep3.5 _BigDecimal_]

# 1.增加jep依赖 #

<dependency>
    			<groupId>org.scijava</groupId>
    			<artifactId>jep</artifactId>
    			<version>2.4.2</version>
    		</dependency>

# 2.计算公式   #

JEP本身支持的函数 如果没有需要的函数  下文有自定义函数实现

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDQ2MTI4MQ_size_16_color_FFFFFF_t_70][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDQ2MTI4MQ_size_16_color_FFFFFF_t_70 1][]

计算 M12\*3.14/4\*pow(O5,2)\*(K11+273-G11)/(G12\*sqrt(3.14\*M11\*P11)) 的值  够复杂吧

public static void main(String[] args) {
            JEP jep = new JEP();
            // 添加常用函数
            jep.addStandardFunctions();
            // 添加常用常量
            jep.addStandardConstants();
    
            String exp = "M12*3.14/4*pow(O5,2)*(K11+273-G11)/(G12*sqrt(3.14*M11*P11))"; //给变量赋值
            jep.addVariable("M12", 1.1);
            jep.addVariable("O5", 11.28665296);
            jep.addVariable("K11", 25);
            jep.addVariable("G11", 200);
            jep.addVariable("G12", 100000);
            jep.addVariable("M11", 0.000000129);
            jep.addVariable("P11", 10);
    
            try { //执行
                jep.parseExpression(exp);
                double result = jep.getValue();
                System.out.println("计算结果： " + result);
            } catch (Throwable e) {
                System.out.println("An error occured: " + e.getMessage());
            }
        }

![20200417171550993.png][]

完全不是问题

# 3.实现自定义函数 min max #

min函数 两数取最小值

public class Min extends PostfixMathCommand {
            public Min() {
                super();
                // 使用参数的数量
                numberOfParameters = 2;
            }
    
            @Override
            public void run(Stack inStack) throws ParseException {
                //检查栈
                checkStack(inStack);
                Object param2 = inStack.pop();
                Object param1 = inStack.pop();
    
                if ((param1 instanceof Number) && (param2 instanceof Number)) {
                    double p1 = ((Number) param2).doubleValue();
                    double p2 = ((Number) param1).doubleValue();
    
                    double result = Math.min(p1, p2);
    
                    inStack.push(new Double(result));
                } else {
                    throw new ParseException("Invalid parameter type");
                }
                return;
            }
    
        }

max函数 两数取最大值

static class Max extends PostfixMathCommand {
            public Max() {
                super();
                // 使用参数的数量
                numberOfParameters = 2;
            }
    
            @Override
            public void run(Stack inStack) throws ParseException {
                //检查栈
                checkStack(inStack);
                Object param2 = inStack.pop();
                Object param1 = inStack.pop();
    
                if ((param1 instanceof Number) && (param2 instanceof Number)) {
                    double p1 = ((Number) param2).doubleValue();
                    double p2 = ((Number) param1).doubleValue();
    
                    double result = Math.max(p1, p2);
    
                    inStack.push(new Double(result));
                } else {
                    throw new ParseException("Invalid parameter type");
                }
                return;
            }
    
        }

验证是否好用

public static void main(String[] args) {
            JEP jep = new JEP();
            // 添加常用函数
            jep.addStandardFunctions();
            // 添加常用常量
            jep.addStandardConstants();
            // 添加自定义函数
            jep.addFunction("min", new Min());
            jep.addFunction("max", new Max());
    
            String min = "min(A1,A2)";
            String max = "max(A1,A2)";
            jep.addVariable("A1", 1.1);
            jep.addVariable("A2", 2.3);
    
            try { //执行
                jep.parseExpression(min);
                double minResult = jep.getValue();
                jep.parseExpression(max);
                double maxResult = jep.getValue();
                System.out.println("最小值为： " + minResult);
                System.out.println("最大值为： " + maxResult);
            } catch (Throwable e) {
                System.out.println("An error occured: " + e.getMessage());
            }
        }

![20200417172248866.png][]

完全没问题

[java _ jep3.5 _BigDecimal_]: https://blog.csdn.net/weixin_40461281/article/details/106073756
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDQ2MTI4MQ_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/202004171725129.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDQ2MTI4MQ==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDQ2MTI4MQ_size_16_color_FFFFFF_t_70 1]: /images/20230521/506f259166204583988132998ea1fc87.png
[20200417171550993.png]: /images/20230521/cc9cff62174b4933b86510e7dbf0c8d0.png
[20200417172248866.png]: /images/20230521/85cfcd2643be4150b833a92eedef85b9.png