jeval是為為你的Java應用程式提供可加入的、高性能、數學、 布爾和函數表達式的解析和運算的高級資源包。
最新版本： 0.9.3測試版
public static void main(String args[]) {
/*
* This sample shows the basic usage of the JEval Evaluator class.
* Calling the default contructor will set he quoteCharater to single
* quote. This constructor will also load all math variables, math
* functions and string variables.
*/
Evaluator evaluator = new Evaluator();
try {
/**
* 添加變量到 Evaluator 類實例.
*/
evaluator.putVariable("a", "'Hello'");
evaluator.putVariable("b", "'World'");
/**
* 簡單輸出變量.
*/
System.out.println(evaluator.evaluate("#{a}"));
System.out.println(evaluator.evaluate("#{b}"));
/**
* 簡單輸出數學常量.
*/
System.out.println(evaluator.evaluate("#{PI}"));
/**
* 字符串拼裝.
*/
System.out.println(evaluator.evaluate("#{a} + ' ' + #{b} + '!'"));
/**
* This sample clears the variables. This call will not clear
* preloaded variables.
*/
evaluator.clearVariables();
/**
* 自定義變量.
*/
evaluator.setVariableResolver(new MockVariableResolver());
System.out.println(evaluator
.evaluate("#{MockVariable1} + #{MockVariable2}"));
/**
* This sample shows an invalid expression. The variables were just
* cleared, therefor the variable "a" no longer exists.
*/
System.out.println("An exception is expected in the "
+ "next evaluation.");
System.out.println(evaluator.evaluate("#{a}"));
} catch (EvaluationException ee) {
System.out.println(ee);
}
}
類MockVariableResolver的內容：
/**
* This clas is an example of a custom variable resolver that can set onto an
* instance of an evaluator.
*/
public class MockVariableResolver implements VariableResolver {
/**
* Returns a variable value for the specified variable name.
*
* @param variableName
* The name of the variable to return the variable value for.
*
* @return A variable value for the specified variable name. If the variable
* name can not be resolved, then null should be returned.
*
* @throws Can throw a FunctionException if needed.
*/
public String resolveVariable(String variableName) throws FunctionException {
String returnValue = null;
if (variableName.equals("MockVariable1")) {
returnValue = "1";
}
else if (variableName.equals("MockVariable2")) {
returnValue = "2";
}
else if (variableName.equals("MockVariable3")) {
throw new FunctionException("Invalid mock variable name.");
}
return returnValue;
}
}
帶數學操作符舉例：
public static void main(String args[]) {
/*
* This sample shows the basic usage of the JEval Evaluator class.
* Calling the default contructor will set he quoteCharater to single
* quote. This constructor will also load all math variables, math
* functions and string variables.
*/
Evaluator evaluator = new Evaluator();
try {
/*
* This sample shows basic addition.
*
* Note: The output will contain at least one decimal place, since
* the results of math operations are treated like doubles.
*/
System.out.println(evaluator.evaluate("4 + 1"));
/**
* This sample shows basic division
*/
System.out.println(evaluator.evaluate("1 / 3"));
/**
* This sample shows a more complex expression involving
* parentheses.
*/
System.out.println(evaluator.evaluate("4 + (3 + 1) + (3 + 1) + 1"));
/**
* This sample shows an invalid expression. There is no operand to
* the right of the plus addition operator.
*/
System.out.println("An exception is expected in the "
+ "next evaluation.");
System.out.println(evaluator.evaluate("4 + "));
} catch (EvaluationException ee) {
System.out.println(ee);
}
}
遺憾的是，jeval目前只支持數值，布爾，字符串，自定義函數等的操作，但並不支持日期類型的操作。
對於變量名包含『{』，『}』等保留符號時候的處理也不好。
期待下一版本能有所改善。