数学工具类

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.math.BigDecimal;
import java.text.DecimalFormat;
public class NewMathUtil {
    private static final Logger logger = LoggerFactory.getLogger(NewMathUtil.class);
    /**
     * 自动解析字符串内容并计算，同时可设置保留小数点位数
     *
     * @param operatorStr 运算式，eg. 10/3 or 1*5 or 6+1 or 8-1
     * @param xsdws       保留小数点位数
     * @return
     */
    public static String autoCalc(String operatorStr, int xsdws) {
        char[] chars = "+-*/".toCharArray();
        for (char tempC : chars) {
            String operation = String.valueOf(tempC);
            if (operatorStr.contains(operation)) {
                return calcOperatorChar(operatorStr, xsdws);
            }
        }
        return null;
    }
    /**
     * 自动解析字符串内容并计算，同时可设置保留小数点位数
     *
     * @param operatorStr    运算式，eg. 10/3 or 1*5 or 6+1 or 8-1
     * @param xsdws          保留小数点位数
     * @param bigDecimalRule 小数点的取舍规则
     * @return
     */
    public static String autoCalc(String operatorStr, int xsdws, Integer bigDecimalRule) {
        char[] chars = "+-*/".toCharArray();
        for (char tempC : chars) {
            String operation = String.valueOf(tempC);
            if (operatorStr.contains(operation)) {
                return calcOperatorChar(operatorStr, xsdws, bigDecimalRule);
            }
        }
        return null;
    }
    /**
     * 整数只保留整数，小数统一保留2位小数。
     * eg. "100",   "100.0",  "100.00",  "0",   "0.0",  "0.00",  "0.1",  "0.12", "3", "3.0",  "3.1",  "3.12", "3.345"
     * --> 100，    100，    100，         0，      0，     0，     0.10，  0.12，  3，   3，    3.10，   3.12，  3.34
     *
     * @param rate
     * @return
     */
    public static String keep2DecimalPlacesExceptInteger(String rate) {
        if (rate != null) {
            if (rate.startsWith("100")) {// 100 or 100.0 100.00 --> 100
                rate = "100";
            } else if (rate.equals("0") || rate.equals("0.0") || rate.equals("0.00")) {// 0 or 0.0 or 0.00 --> 0
                rate = "0";
            } else if (rate.endsWith(".0") || rate.endsWith(".00")) {// 3.0 or 3.00 --> 3
                rate = rate.split("\\.")[0];
            } else if (rate.contains(".")) {
                if (rate.split("\\.")[1].length() == 1) {// 3.1 --> 3.10
                    rate += "0";
                } else if (rate.split("\\.")[1].length() > 1) {// 3.345 --> 3.34
                    rate = rate.split("\\.")[0] + "." + rate.split("\\.")[1].substring(0, 2);
                }
            } /*else if (!rate.contains(".")) {// 10 --> 10
                //
            }*/
        }
        return rate;
    }
    /**
     * 功能：输入字符串的计算式得到指定位数的结果
     *
     * @param operator 计算式(如 10/3)
     * @param ws       四舍五入，保留几位小数(默认保留2位小数)
     * @param <T>
     * @return
     */
    public static <T> String calcOperatorChar(String operator, T ws) {
        return method(operator, ws, BigDecimal.ROUND_HALF_UP);
    }
    public static <T> String calcOperatorChar(String operator, T xsdws, Integer bigDecimalRule) {
        if (bigDecimalRule == null) {
            // 小数点保留规则：默认"四舍五入"
            bigDecimalRule = BigDecimal.ROUND_HALF_UP;
        }
        // ROUND_HALF_UP：四舍五入
        // ROUND_HALF_DOWN：五舍六入
        // ROUND_DOWN：直接删除多余的小数位
        // ROUND_UP：进位处理
        return method(operator, xsdws, bigDecimalRule);
    }
    private static <T> String method(String operator, T xsdNum, Integer roundRule) {
        int xsdws = 0;
        if (xsdNum == null) {// 默认保留2位小数
            xsdws = 2;
        } else if (xsdNum instanceof Integer) {
            xsdws = (Integer) xsdNum;
        } else if (xsdNum instanceof String) {
            xsdws = Integer.parseInt((String) xsdNum);
        } else {
            throw new RuntimeException("ws 格式有误(只能为 String or Integer 类型)");
        }
        operator = operator.replaceAll(" ", "");
        String[] split = operator.split("[+,-,*,/]");
        if (split.length != 2 || (split.length == 2 && operator.length() - split[0].length() - split[1].length() != 1)) {
            throw new RuntimeException("运算符非 +-*/ 中的一种 or 存在多个运算符 or 运算式有误");
        }
        String s1 = split[0];
        String s2 = split[1];
        BigDecimal bigDecimal = null;
        if (operator.contains("+")) {
            bigDecimal = new BigDecimal(s1).add(new BigDecimal(s2));
        } else if (operator.contains("-")) {
            bigDecimal = new BigDecimal(s1).subtract(new BigDecimal(s2));
        } else if (operator.contains("*")) {
            bigDecimal = new BigDecimal(s1).multiply(new BigDecimal(s2));
        } else if (operator.contains("/")) {
            bigDecimal = new BigDecimal(s1).divide(new BigDecimal(s2), xsdws, roundRule != null ? roundRule : BigDecimal.ROUND_HALF_UP);
        } else {
            throw new RuntimeException("operator not contains +-*/");
        }
        return keepXSD(xsdws, bigDecimal);
    }
    private static <T> String keepXSD(int xsdCount, T num) {
        StringBuilder zwf = new StringBuilder().append("#0.");// 占位符
        for (int i = 0; i < xsdCount; i++) {
            zwf.append("0");
        }
        BigDecimal bigDecimal = null;
        if (num instanceof String) {
            bigDecimal = new BigDecimal((String) num);
        } else if (num instanceof BigDecimal) {
            bigDecimal = (BigDecimal) num;
        } else if (num instanceof Long) {
            bigDecimal = new BigDecimal((Long) num);
        } else if (num instanceof Float) {
            bigDecimal = new BigDecimal((Float) num);
        } else if (num instanceof Double) {
            bigDecimal = new BigDecimal((Double) num);
        } else {
            throw new RuntimeException("num 只支持 int、long、double、float、String 几种类型");
        }
        String format = new DecimalFormat(zwf.toString()).format(bigDecimal);
        // .123 ==> 0.123
        if (format.startsWith(".")) {
            format = "0" + format;
        }
        // 10. ==> 10
        if (format.endsWith(".")) {
            format = format.substring(0, format.length() - 1);
        }
        return format;
    }
}