计算数学公式的工具

import java.math.BigDecimal;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 计算数学公式的工具
 * 
 * @author Ruffian Jiang
 *
 */
public class CalculatorUtil {

    public static BigDecimal arithmetic(String exp) {
        if (!exp.matches("\\d+")) {
            String result = parseExp(exp);
            if (result != null) {
                result = result.replaceAll("[\\[\\]]", "");
            }else{
                result = "0";
            }
            return new BigDecimal(result);
        } else {
            return new BigDecimal(exp);
        }
    }

    /**
     * 最小计数单位
     * 
     */
    private static String minExp = "^((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))$";
    /**
     * 不带括号的运算
     */
    private static String noParentheses = "^[^\\(\\)]+$";
    /**
     * 匹配乘法或者除法
     */
    private static String priorOperatorExp = "(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";
    /**
     * 匹配加法和减法
     */
    private static String operatorExp = "(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";
    /**
     * 匹配只带一个括号的
     */
    private static String minParentheses = "\\([^\\(\\)]+\\)";

    /**
     * 解析计算四则运算表达式，例：2+((3+4)*2-22)/2*3
     * 
     * @param expression
     * @return
     */
    private static String parseExp(String expression) {
        // 方法进入 先替换空格，在去除运算两边的()号
        expression = expression.replaceAll("\\s+", "").replaceAll("^\\(([^\\(\\)]+)\\)$", "$1");

        // 最小表达式计算
        if (expression.matches(minExp)) {
            String result = calculate(expression);
            return Double.parseDouble(result) >= 0 ? result : "[" + result + "]";
        }
        // 计算不带括号的四则运算
        if (expression.matches(noParentheses)) {
            Pattern patt = Pattern.compile(priorOperatorExp);
            Matcher mat = patt.matcher(expression);
            if (mat.find()) {
                String tempMinExp = mat.group();
                expression = expression.replaceFirst(priorOperatorExp, parseExp(tempMinExp));
            } else {
                patt = Pattern.compile(operatorExp);
                mat = patt.matcher(expression);

                if (mat.find()) {
                    String tempMinExp = mat.group();
                    expression = expression.replaceFirst(operatorExp, parseExp(tempMinExp));
                }
            }
            return parseExp(expression);
        }

        // 计算带括号的四则运算
        Pattern patt = Pattern.compile(minParentheses);
        Matcher mat = patt.matcher(expression);
        if (mat.find()) {
            String tempMinExp = mat.group();
            expression = expression.replaceFirst(minParentheses, parseExp(tempMinExp));
        }
        return parseExp(expression);
    }

    /**
     * 计算最小单位四则运算表达式（两个数字）
     * 
     * @param exp
     * @return
     */
    private static String calculate(String exp) {
        exp = exp.replaceAll("[\\[\\]]", "");
        String number[] = exp.replaceFirst("(\\d)[\\+\\-\\*\\/]", "$1,").split(",");
        BigDecimal number1 = new BigDecimal(number[0]);
        BigDecimal number2 = new BigDecimal(number[1]);
        BigDecimal result = null;

        String operator = exp.replaceFirst("^.*\\d([\\+\\-\\*\\/]).+$", "$1");
        if ("+".equals(operator)) {
            result = number1.add(number2);
        } else if ("-".equals(operator)) {
            result = number1.subtract(number2);
        } else if ("*".equals(operator)) {
            result = number1.multiply(number2);
        } else if ("/".equals(operator)) {
            // 第二个参数为精度，第三个为四色五入的模式
            result = number1.divide(number2, 5, BigDecimal.ROUND_CEILING);
        }

        return result != null ? result.toString() : null;
    }

    public static void main(String[] args) {
        String ss = "2+((3+4)*2-22)/2*3";
        String ss1 = "3-2";
        System.out.println(arithmetic(ss));
    }

}