public class FormulaTest {
@Test
public void testFormula() {
//基礎數據
Map<String, BigDecimal> values = new HashMap<String, BigDecimal>();
values.put("dddd", BigDecimal.valueOf(56d));

//需要依賴的其他公式
Map<String, String> formulas = new HashMap<String, String>();
formulas.put("eeee", "#{dddd}*20");

//需要計算的公式
String expression = "#{eeee}*-12+13-#{dddd}+24";

BigDecimal result = FormulaParser.parse(expression, formulas, values);
Assert.assertEquals(result, BigDecimal.valueOf(-13459.0));
}
}

public class FormulaParser {
/**
* 匹配變量占位符的正則表達式
*/
private static Pattern pattern = Pattern.compile("\\#\\{(.+?)\\}");

/**
* 解析公式，并執行公式計算
*
* @param formula
* @param formulas
* @param values
* @return
*/
public static BigDecimal parse(String formula, Map<String, String> formulas, Map<String, BigDecimal> values) {
if (formulas == null)formulas = Collections.emptyMap();
if (values == null)values = Collections.emptyMap();
String expression = finalExpression(formula, formulas, values);
return new Calculator().eval(expression);
}

/**
* 解析公式，并執行公式計算
*
* @param formula
* @param values
* @return
*/
public static BigDecimal parse(String formula, Map<String, BigDecimal> values) {
if (values == null)values = Collections.emptyMap();
return parse(formula, Collections.<String, String> emptyMap(), values);
}

/**
* 解析公式，并執行公式計算
*
* @param formula
* @return
*/
public static BigDecimal parse(String formula) {
return parse(formula, Collections.<String, String> emptyMap(), Collections.<String, BigDecimal> emptyMap());
}

/**
* 將所有中間變量都替換成基礎數據
*
* @param expression
* @param formulas
* @param values
* @return
*/
private static String finalExpression(String expression, Map<String, String> formulas, Map<String, BigDecimal> values) {
Matcher m = pattern.matcher(expression);
if (!m.find())return expression;

m.reset();

StringBuffer buffer = new StringBuffer();
while (m.find()) {
String group = m.group(1);
if (formulas != null && formulas.containsKey(group)) {
String formula = formulas.get(group);
m.appendReplacement(buffer, '(' + formula + ')');
} else if (values != null && values.containsKey(group)) {
BigDecimal value = values.get(group);
m.appendReplacement(buffer,value.toPlainString());
}else{
throw new IllegalArgumentException("expression '"+expression+"' has a illegal variable:"+m.group()+",cause veriable '"+group+"' not being found in formulas or in values.");
}
}
m.appendTail(buffer);
return finalExpression(buffer.toString(), formulas, values);
}
}

public class Calculator{
private static Log logger = LogFactory.getLog(Calculator.class);

/**
* 左括號
*/
public final static char LEFT_BRACKET = '(';

/**
* 右括號
*/
public final static char RIGHT_BRACKET = ')';

/**
* 中綴表達式中的空格，需要要忽略
*/
public final static char BLANK = ' ';

/**
* 小數點符號
*/
public final static char DECIMAL_POINT = '.';

/**
* 負號
*/
public final static char NEGATIVE_SIGN = '-';

/**
* 正號
*/
public final static char POSITIVE_SIGN = '+';

/**
* 后綴表達式的各段的分隔符
*/
public final static char SEPARATOR = ' ';

/**
* 解析并計算表達式
*
* @param expression
* @return
*/
public BigDecimal eval(String expression) {
String str = infix2Suffix(expression);
logger.info("Infix Expression: " + expression);
logger.info("Suffix Expression: " + str);
if (str == null) {
throw new IllegalArgumentException("Infix Expression is null!");
}
return evalInfix(str);
}

/**
* 對后綴表達式進行計算
*
* @param expression
* @return
*/
private BigDecimal evalInfix(String expression) {
String[] strs = expression.split("\\s+");
Stack<String> stack = new Stack<String>();
for (int i = 0; i < strs.length; i++) {
if (!Operator.isOperator(strs[i])) {
stack.push(strs[i]);
} else {
Operator op = Operator.getInstance(strs[i]);
BigDecimal right =new BigDecimal(stack.pop());
BigDecimal left =new BigDecimal(stack.pop());
BigDecimal result = op.eval(left, right);
stack.push(String.valueOf(result));
}
}
return new BigDecimal(stack.pop());
}

/**
* 將中綴表達式轉換為后綴表達式<br>
* 具體算法規則 81 * 1)計算機實現轉換： 將中綴表達式轉換為后綴表達式的算法思想：
* 開始掃描；
* 數字時，加入后綴表達式；
* 運算符：
* a.若為 '('，入棧；
* b.若為 ')'，則依次把棧中的的運算符加入后綴表達式中，直到出現'('，從棧中刪除'(' ；
* c.若為 除括號外的其他運算符 ，當其優先級高于棧頂運算符時，直接入棧。否則從棧頂開始，依次彈出比當前處理的運算符優先級高和優先級相等的運算符，直到一個比它優先級低的或者遇到了一個左括號為止。
* ·當掃描的中綴表達式結束時，棧中的的所有運算符出棧；　
*
* @param expression
* @return
*/
public String infix2Suffix(String expression) {
if (expression == null) return null;

Stack<Character> stack = new Stack<Character>();

char[] chs = expression.toCharArray();
StringBuilder sb = new StringBuilder(chs.length);

boolean appendSeparator = false;
boolean sign = true;
for (int i = 0; i < chs.length; i++) {
char c = chs[i];

// 空白則跳過
if (c == BLANK)continue;

// Next line is used output stack information.
// System.out.printf("%-20s %s%n", stack, sb.toString());

// 添加后綴表達式分隔符
if (appendSeparator) {
sb.append(SEPARATOR);
appendSeparator = false;
}

if (isSign(c) && sign) {
sb.append(c);
} else if (isNumber(c)) {
sign = false;// 數字后面不是正號或負號，而是操作符+-
sb.append(c);
} else if (isLeftBracket(c)) {
stack.push(c);
} else if (isRightBracket(c)) {
sign = false;

// 如果為)，則彈出(上面的所有操作符，并添加到后綴表達式中，并彈出(
while (stack.peek() != LEFT_BRACKET) {
sb.append(SEPARATOR).append(stack.pop());
}
stack.pop();
} else {
appendSeparator = true;
if (Operator.isOperator(c)) {
sign = true;

// 若為(則入棧
if (stack.isEmpty() || stack.peek() == LEFT_BRACKET) {
stack.push(c);
continue;
}
int precedence = Operator.getPrority(c);
while (!stack.isEmpty() && Operator.getPrority(stack.peek()) >= precedence) {
sb.append(SEPARATOR).append(stack.pop());
}
stack.push(c);
}
}
}
while (!stack.isEmpty()) {
sb.append(SEPARATOR).append(stack.pop());
}
return sb.toString();
}

/**
* 判斷某個字符是否是正號或者負號
*
* @param c
* @return
*/
private boolean isSign(char c) {
return (c == NEGATIVE_SIGN || c == POSITIVE_SIGN);
}

/**
* 判斷某個字符是否為數字或者小數點
*
* @param c
* @return
*/
private boolean isNumber(char c) {
return ((c >= '0' && c <= '9') || c == DECIMAL_POINT);
}

/**
* 判斷某個字符是否為左括號
*
* @param c
* @return
*/
private boolean isLeftBracket(char c) {
return c == LEFT_BRACKET;
}

/**
* 判斷某個字符是否為右括號
*
* @param c
* @return
*/
private boolean isRightBracket(char c) {
return c == RIGHT_BRACKET;
}

View Code
public abstract class Operator {
/**
* 運算符
*/
private char operator;

/**
* 運算符的優先級別，數字越大，優先級別越高
*/
private int priority;

private static Map<Character, Operator> operators = new HashMap<Character, Operator>();

private Operator(char operator, int priority) {
setOperator(operator);
setPriority(priority);
register(this);
}

private void register(Operator operator) {
operators.put(operator.getOperator(), operator);
}

/**
* 加法運算
*/
public final static Operator ADITION = new Operator('+', 100) {
public BigDecimal eval(BigDecimal left, BigDecimal right) {
return left.add(right);
}
};

/**
* 減法運算
*/
public final static Operator SUBTRATION = new Operator('-', 100) {
public BigDecimal eval(BigDecimal left, BigDecimal right) {
return left.subtract(right);
}
};

/**
* 乘法運算
*/
public final static Operator MULTIPLICATION = new Operator('*', 200) {
public BigDecimal eval(BigDecimal left, BigDecimal right) {
return left.multiply(right);
}
};

/**
* 除法運算
*/
public final static Operator DIVITION = new Operator('/', 200) {
public BigDecimal eval(BigDecimal left, BigDecimal right) {
return left.divide(right);
}
};

/**
* 冪運算
*/
public final static Operator EXPONENT = new Operator('^', 300) {
public BigDecimal eval(BigDecimal left, BigDecimal right) {
return left.pow(right.intValue());
}
};

public char getOperator() {
return operator;
}

private void setOperator(char operator) {
this.operator = operator;
}

public int getPriority() {
return priority;
}

private void setPriority(int priority) {
this.priority = priority;
}

/**
* 根據某個運算符獲得該運算符的優先級別
*
* @param c
* @return 運算符的優先級別
*/
public static int getPrority(char c) {
Operator op = operators.get(c);
return op != null ? op.getPriority() : 0;
}

/**
* 工具方法，判斷某個字符是否是運算符
*
* @param c
* @return 是運算符返回 true，否則返回 false
*/
public static boolean isOperator(char c) {
return getInstance(c) != null;
}

public static boolean isOperator(String str) {
return str.length() > 1 ? false : isOperator(str.charAt(0));
}

/**
* 根據運算符獲得 Operator 實例
*
* @param c
* @return 從注冊中的 Operator 返回實例，尚未注冊返回 null
*/
public static Operator getInstance(char c) {
return operators.get(c);
}

public static Operator getInstance(String str) {
return str.length() > 1 ? null : getInstance(str.charAt(0));
}

/**
* 根據操作數進行計算
*
* @param left
* 左操作數
* @param right
* 右操作數
* @return 計算結果
*/
public abstract BigDecimal eval(BigDecimal left, BigDecimal right);