Fel是支持表达式计算的一个库(java)。

Fel支持解释执行和编译执行，可以根据性能要求选择执行方式。

下面给出示例和性能测试数据：

package datagene;

import java.util.Random;

import com.greenpineyu.fel.Expression;

import com.greenpineyu.fel.FelEngine;

import com.greenpineyu.fel.FelEngineImpl;

import com.greenpineyu.fel.context.FelContext;

import com.greenpineyu.fel.parser.FelNode;

public class Expr {

public static void main(String[] args) {

Random random = new Random();

Object result = null;

long time = System.nanoTime();

for(int i = 0; i < 200000000; i++) {

result = random.nextInt(1000) * random.nextInt(1000) +

random.nextInt(1000);

}

System.out.println(((float)(System.nanoTime() - time) / 1000000) + "ms");

FelEngine fel1 = new FelEngineImpl();

FelContext ctx1 = fel1.getContext();

time = System.nanoTime();

for(int i = 0; i < 1000000; i++) {

ctx1.set("a", random.nextInt(1000));

ctx1.set("b", random.nextInt(1000));

ctx1.set("c", random.nextInt(1000));

result = fel1.eval("a * b + c");

}

System.out.println(((float)(System.nanoTime() - time) / 1000000) + "ms");

FelEngine fel2 = new FelEngineImpl();

FelNode node = fel2.parse("a * b + c");

FelContext ctx2 = fel2.getContext();

time = System.nanoTime();

for(int i = 0; i < 200000000; i++) {

ctx2.set("a", random.nextInt(1000));

ctx2.set("b", random.nextInt(1000));

ctx2.set("c", random.nextInt(1000));

result = node.eval(ctx2);

}

System.out.println(((float)(System.nanoTime() - time) / 1000000) + "ms");

FelEngine fel3 = new FelEngineImpl();

Expression exp = fel3.parse("a * b + c");

FelContext ctx3 = fel3.getContext();

time = System.nanoTime();

for(int i = 0; i < 200000000; i++) {

ctx3.set("a", random.nextInt(1000));

ctx3.set("b", random.nextInt(1000));

ctx3.set("c", random.nextInt(1000));

result = exp.eval(ctx3);

}

System.out.println(((float)(System.nanoTime() - time) / 1000000) + "ms");

}

}

输出：