javaassist动态注入代码

缺乏、安全感 2023-10-07 08:45 13阅读 0赞

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);
        }
    }