修改方法

package org.test;

/**
 * Created by sky on 15-12-31.
 */
public class Bool {

    public static void main(String[] args) throws InterruptedException {
        new Bool().run();
    }

    public void run() throws InterruptedException {
        Thread.sleep(1000 * 5);
        System.out.println("default");
    }
}

为方法前后添加性能统计时间

package org.javassist.demo;

import javassist.*;

import java.io.IOException;

/**
 * Created by sky on 15-12-31.
 */
public class ReadByteCode {
    public static void main(String[] args) throws NotFoundException, CannotCompileException, IOException {
        ClassPool classPool = ClassPool.getDefault();
        classPool.importPackage("org.test");
        CtClass ctClass = null;
        try {
            ctClass = classPool.get("org.test.Bool");
        } catch (NotFoundException e) {
            e.printStackTrace();
        }
        CtMethod[] methods = ctClass.getDeclaredMethods();
        for (int i = 0; i < methods.length; i++) {
            CtMethod method = methods[i];
            String methodName = method.getName();
            String oldMethodName = methodName + "$$old";
            if (!"main".equalsIgnoreCase(methodName)) {
                CtMethod newMehtod = CtNewMethod.copy(method, ctClass, null);
                method.setName(oldMethodName);
                StringBuilder sb = new StringBuilder(100);
                sb.append("{\nlong s = System.currentTimeMillis();\n");
                sb.append(oldMethodName + "($$);\n");
                sb.append("System.out.println(\"Call to method " + methodName
                        + " took \" +\n (System.currentTimeMillis()-s) + "
                        + "\" ms.\");\n");

                sb.append("}");
                newMehtod.setBody(sb.toString());
                newMehtod.setName(methodName);
                ctClass.addMethod(newMehtod);
            }
        }
        ctClass.writeFile("/tmp/hello");
    }
}

运行完后，就可以看到/tmp/hello目录下有个class文件了，如下:

└─[0] <> tree /tmp/hello
/tmp/hello
└── org
    └── test
        └── Bool.class

2 directories, 1 file

运行结果如下:

└─[0] <> java org.test.Bool
default
Call to method run took 5001 ms.