记一次Agent之旅

public class CheckLicense {
    private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    private static boolean checkExpiry(String expireDate) throws ParseException {
        try {
            Date date = DATE_FORMAT.parse(expireDate);
            // 检测当前系统时间早于License授权截至时间
            if (new Date().before(date)) {
                return false;
            }
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return true;
    }

    public static void main(String[] args) {
        // 设置一个已经过期的License时间
        final String expireDate = "2020-10-01 00:00:00";

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        String time = "[" + DATE_FORMAT.format(new Date()) + "] ";
                        // 检测license是否已经过期
                        try {
                            if (checkExpiry(expireDate)) {
                                System.err.println(time + "您的授权已过期，请重新购买授权！");
                            } else {
                                System.out.println(time + "您的授权正常，截止时间为：" + expireDate);
                            }
                        } catch (ParseException e) {
                            e.printStackTrace();
                        }

                        // sleep 1秒
                        TimeUnit.SECONDS.sleep(1);

                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
}

public class MyAgent3 {
    private static final String HookClass = "CheckLicense";
    public static void premain(String agentArgs, Instrumentation inst) {
        inst.addTransformer(new MyClassFileTransformer());
    }

    public static class MyClassFileTransformer implements ClassFileTransformer{

        @Override
        public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
            String newClassName = className.replace("/",".");
            if(newClassName.equals(HookClass)){
                System.out.println("Hook: "+HookClass);
                ClassPool classPool = ClassPool.getDefault();
                try {
                    CtClass ctClass = classPool.makeClass(new ByteArrayInputStream(classfileBuffer));
                    CtMethod ctMethod = ctClass.getDeclaredMethod("checkExpiry",new CtClass[]{classPool.getCtClass("java.lang.String")});
                    ctMethod.insertBefore("return false;");
                    classfileBuffer = ctClass.toBytecode();

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            return classfileBuffer;
        }
    }
}

public class MyAgent4 {
    public static  String HookClass = "CheckLicense" ;
    public static void main(String[] args)throws Exception {
        // 拿到agent的绝对路径
        URL agentURL = MyAgent4.class.getProtectionDomain().getCodeSource().getLocation();
        String agentPath = new File(agentURL.toURI()).getAbsolutePath();

        List<VirtualMachineDescriptor> list = VirtualMachine.list();
        for (VirtualMachineDescriptor desc : list) {
            if(desc.displayName().equals(HookClass)){
                String pid = desc.id();
                System.out.println("进程名称：" + HookClass+", 进程ID：" + pid);
                VirtualMachine vm = VirtualMachine.attach(pid);
                vm.loadAgent(agentPath);
                vm.detach();
            }
        }
    }
    public static void agentmain(String args, final Instrumentation inst) {
        // 添加自定义的Transformer，第二个参数true表示是否允许Agent Retransform，
        // 需配合MANIFEST.MF中的Can-Retransform-Classes: true配置
        inst.addTransformer(new MyClassFileTransformer(), true);
        // 获取所有已经被JVM加载的类对象
        Class[] loadedClass = inst.getAllLoadedClasses();
        for (Class clazz : loadedClass) {
            String className = clazz.getName();
            if (inst.isModifiableClass(clazz)) {
                // 使用Agent重新加载HelloWorld类的字节码
                if (className.equals(HookClass)) {
                    try {
                        inst.retransformClasses(clazz);
                    }catch (UnmodifiableClassException e){
                        e.printStackTrace();
                    }
                }
            }
        }
    }
    public static class MyClassFileTransformer implements ClassFileTransformer {
        @Override
        public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
            String newClassName = className.replace("/",".");
            if(newClassName.equals(HookClass)){
                System.out.println("Hook: "+HookClass);
                ClassPool classPool = ClassPool.getDefault();
                try {
                    CtClass ctClass = classPool.makeClass(new ByteArrayInputStream(classfileBuffer));
                    CtMethod ctMethod = ctClass.getDeclaredMethod("checkExpiry",new CtClass[]{classPool.getCtClass("java.lang.String")});
                    ctMethod.setBody("return false;");
                    classfileBuffer = ctClass.toBytecode();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            return classfileBuffer;
        }
    }
}