利用ScriptEngineManager实现字符串公式灵活计算的方法

A+B*C 

A=1,B=2,C=3

public Double Calculation(String formula){
Double result=null; //计算结果
ScriptEngineManager manager = new ScriptEngineManager(); //创建一个ScriptEngineManager对象
ScriptEngine engine = manager.getEngineByName("js"); //通过ScriptEngineManager获得ScriptEngine对象
try {
result = (Double) engine.eval(formula); //用ScriptEngine的eval方法执行脚本
} catch (ScriptException e) {
this.isSuccess=false;
result=Double.NaN;
} 
return result;
}

/**
 * 精确替换字符 防止出现 匹配A 时将AA匹配的情况
 */

public static String replaceStr(String sourceStr,String replaceKey,String replaceValue){
String replaceStrReg="";
for(char str_char:replaceKey.toCharArray()){
replaceStrReg+="[";
replaceStrReg+=str_char;
replaceStrReg+="]";
}
String startReg="^"+replaceStrReg+"([\\+\\-\\*/,)])";
String endReg="([\\+\\-\\*/,(])"+replaceStrReg+"$";
String reg="([^a-zA-Z])("+replaceStrReg+")"+"([^a-zA-Z])";
String endStr=sourceStr;
while(matcheStr(endStr,replaceKey)){
endStr=endStr.replaceAll(startReg, replaceValue+"$1");
endStr=endStr.replaceAll(reg, "$1"+replaceValue+"$3");
endStr=endStr.replaceAll(endReg, "$1"+replaceValue);
}
return endStr;
}

/**
* 精确匹配字符 防止出现 匹配A 时将AA匹配的情况
*/
public static Boolean matcheStr(String sourceStr,String matchStr){
String replaceStrReg="";
for(char str_char:matchStr.toCharArray()){
replaceStrReg+="[";
replaceStrReg+=str_char;
replaceStrReg+="]";
}
String startReg="^"+replaceStrReg+"([\\+\\-\\*/,)])[\\s\\S]*";
String endReg="[\\s\\S]*([\\+\\-\\*/,(])"+replaceStrReg+"$";
String reg="[\\s\\S]*([^A-Za-z])("+replaceStrReg+")"+"([^A-Za-z])[\\s\\S]*";
if(sourceStr.matches(startReg)||sourceStr.matches(reg)||sourceStr.matches(endReg)){
return true;
}else{
return false;
}
}

public Map<String,Object> myFunction(String formula){
ScriptEngineManager manager = new ScriptEngineManager(); 
ScriptEngine engine = manager.getEngineByName("js"); 
Object result;
try {
engine.eval(formula);
Invocable inv = (Invocable) engine;
result=inv.invokeFunction("js"); 
Object function = engine.get("useFunction");
map.put("result", result);
map.put("function", function);
} catch (Exception e) {
result=Double.NaN;
} 
return map;
}