代码的思路是通过正则判断计算每个最小的计算单元。以下是代码：
package cn.com.lawchat.forpublicmvc.util; import java.math.BigDecimal; import java.util.regex.Matcher; import java.util.regex.Pattern; /** * 计算器工具类 * @author shuqi * @date 2015-7-23 * @version since 1.0 */ public class CalculatorUtil { public static BigDecimal arithmetic(String exp){ if(!exp.matches(numberString)){ String result = parseExp(exp).replaceAll("[\\[\\]]", ""); 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="\\([^\\(\\)]+\\)"; /** * 匹配只带一个只有半边括号的 */ private static String baseParentheses="^\\(+[^\\)]+$|^[^\\(]+\\)+$"; /** * 匹配存数字 */ private static String numberString = "\\d+\\.\\d+|\\d+"; /** * 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){ //半边括号 直接跑异常 if(expression.matches(baseParentheses)){ throw new RuntimeException("计算公式存在错误，***半边括号！"); } //直接是数字不计算 if(expression.matches(numberString)){ return 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; } }