java eval 字符串 运算

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http://www.ixueyun.com/community/home-space-uid-11902-do-blog-id-1923.html

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http://www.4ucode.com/Study/Topic/450127

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public class Eval {        public Object eval2(String s) throws ScriptException, NoSuchMethodException{    if (s.replaceAll("[\\d+-\\\\*/()]","").equals("")) {                    ScriptEngineManager manager = new ScriptEngineManager();                ScriptEngine engine = manager.getEngineByName("JavaScript");                engine.eval("function t() {return " + s + ";}");                Invocable invocable = (Invocable) engine;                Object o = invocable.invokeFunction("t");                return o;            }    return null;    }        /**     * 计算字符串四则运算表达式     * @param string     * @return     * @author ZYWANG 2009-8-31     */    public String eval(String string) {    String regexCheck = "[\\(\\)\\d\\+\\-\\*/\\.]*";// 是否是合法的表达式    if (!Pattern.matches(regexCheck, string))    return string;    Matcher matcher = null;    String temp = "";    int index = -1;    String regex = "\\([\\d\\.\\+\\-\\*/]+\\)";// 提取括号表达式    string = string.replaceAll("\\s", "");// 去除空格    try {    Pattern pattern = Pattern.compile(regex);    // 循环计算所有括号里的表达式    while (pattern.matcher(string).find()) {    matcher = pattern.matcher(string);    while (matcher.find()) {    temp = matcher.group();    index = string.indexOf(temp);    string = string.substring(0, index)    + computeStirngNoBracket(temp)    + string.substring(index + temp.length());    }    }    // 最后计算总的表达式结果    string = computeStirngNoBracket(string);    } catch (NumberFormatException e) {    return e.getMessage();    }    return string;    }    /**     * 计算不包含括号的表达式     * @param string     * @return     * @author ZYWANG 2009-8-31     */    private  String computeStirngNoBracket(String string) {    string = string.replaceAll("(^\\()|(\\)$)", "");    String regexMultiAndDivision = "[\\d\\.]+(\\*|\\/)[\\d\\.]+";    String regexAdditionAndSubtraction = "(^\\-)?[\\d\\.]+(\\+|\\-)[\\d\\.]+";    String temp = "";    int index = -1;    // 解析乘除法    Pattern pattern = Pattern.compile(regexMultiAndDivision);    Matcher matcher = null;    while (pattern.matcher(string).find()) {    matcher = pattern.matcher(string);    if (matcher.find()) {    temp = matcher.group();    index = string.indexOf(temp);    string = string.substring(0, index) + doMultiAndDivision(temp)    + string.substring(index + temp.length());    }    }    // 解析加减法    pattern = Pattern.compile(regexAdditionAndSubtraction);    while (pattern.matcher(string).find()) {    matcher = pattern.matcher(string);    if (matcher.find()) {    temp = matcher.group();    index = string.indexOf(temp);    if (temp.startsWith("-")) {    string = string.substring(0, index)    + doNegativeOperation(temp)    + string.substring(index + temp.length());    } else {    string = string.substring(0, index)    + doAdditionAndSubtraction(temp)    + string.substring(index + temp.length());    }    }    }    return string;    }    /**     * 执行乘除法     * @param string     * @return     * @author ZYWANG 2009-8-31     */    private  String doMultiAndDivision(String string) {    String value = "";    double d1 = 0;    double d2 = 0;    String[] temp = null;    if (string.contains("*")) {    temp = string.split("\\*");    } else {    temp = string.split("/");    }    if (temp.length < 2)    return string;    d1 = Double.valueOf(temp[0]);    d2 = Double.valueOf(temp[1]);    if (string.contains("*")) {    value = String.valueOf(d1 * d2);    } else {    value = String.valueOf(d1 / d2);    }    return value;    }    /**     * 执行加减法     * @param string     * @return     * @author ZYWANG 2009-8-31     */    private  String doAdditionAndSubtraction(String string) {    double d1 = 0;    double d2 = 0;    String[] temp = null;    String value = "";    if (string.contains("+")) {    temp = string.split("\\+");    } else {    temp = string.split("\\-");    }    if (temp.length < 2)    return string;    d1 = Double.valueOf(temp[0]);    d2 = Double.valueOf(temp[1]);    if (string.contains("+")) {    value = String.valueOf(d1 + d2);    } else {    value = String.valueOf(d1 - d2);    }    return value;    }    /**     * 执行负数运算     * @param string     * @return     * @author ZYWANG 2010-11-8     */    private String doNegativeOperation(String string) {    String temp = string.substring(1);    if (temp.contains("+")) {    temp = temp.replace("+", "-");    } else {    temp = temp.replace("-", "+");    }    temp = doAdditionAndSubtraction(temp);    if (temp.startsWith("-")) {    temp = temp.substring(1);    } else {    temp = "-" + temp;    }    return temp;    }    } Eval eval = new Eval();System.out.println(eval.eval("(1+(2+3)*2/5)*2/7+(3*7-3)*5")); 运行时间:0.007sSystem.out.println(eval.eval2("(1+(2+3)*2/5)*2/7+(3*7-3)*5"));运行时间:0.118s  需要jdk6或者以上