javaassist动态注入代码

package com.zhangxueliang.demo;

import java.io.IOException;

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;
import javassist.NotFoundException;

/**
 * javaassist动态注入代码
 * 
 * @author 张学亮
 *
 */
public class JavassistInsertDemo {

    public static void main(String[] args) throws CannotCompileException, IOException, NotFoundException, InstantiationException, IllegalAccessException {

        ClassPool pool = ClassPool.getDefault();

        // 定义类
        CtClass ctClass = pool.get("com.zhangxueliang.demo.Calculator");

        // 需要修改的方法名称
        String mname = "getSum";
        CtMethod mold = ctClass.getDeclaredMethod(mname);
        // 修改原有的方法名称
        String nname = mname + "New";
        mold.setName(nname);

        //创建新的方法，复制原来的方法
        CtMethod mnew = CtNewMethod.copy(mold, mname, ctClass, null);
        // 主要的注入代码
        StringBuffer body = new StringBuffer();
        body.append("{\nlong start = System.currentTimeMillis();\n");
        // 调用原有代码，类似于method();($$)表示所有的参数
		body.append(nname + "($$);\n");
        body.append("System.out.println(\"Call to method " + mname
                + " took \" +\n (System.currentTimeMillis()-start) + " + "\" ms.\");\n");

        body.append("}");
        // 替换新方法
        mnew.setBody(body.toString());
        // 增加新方法
        ctClass.addMethod(mnew);
        ctClass.writeFile("e:/");

        Calculator calculator =(Calculator)ctClass.toClass().newInstance(); 

        calculator.getSum(100000000);
    }

}

class Calculator {

    public void getSum(long n) {
        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += i;
        }
        System.out.println("n="+n+",sum="+sum);
    }
}