JavaSE反射与动态代理详细代码示例

public class User {
    private String name;
    public Integer age;
    public User(){}
    private User(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    private void setAge(Integer age) {
        this.age = age;
    }
}

        //1.类名.class(编译时确定，最高效)
        Class<?> class1 = User.class;
        System.out.println(class1); //class User
        //2.对象.getClass() (运行时获取，需要实例化)
        User user = new User();
        Class<?> class2 = user.getClass();
        System.out.println(class2); //class User
        //3.Class.forName("全类名") (运行时加载，最灵活)
        Class<?> class3 = Class.forName("User");
        System.out.println(class3); //class User
        //判断上面三种方法获取的是否是同一个对象
        System.out.println(class1.equals(class2)); //true

//1.获取类
        Class<User> userClass = User.class;
        //2.获取构造器
        //2.1获取公共构造器
        Constructor<?>[] publicConstructors = userClass.getConstructors();
        System.out.println(Arrays.toString(publicConstructors)); //[public User()]
        //2.2获取所有构造器
        Constructor<?>[] declaredConstructors = userClass.getDeclaredConstructors();
        System.out.println(Arrays.toString(declaredConstructors)); //[public User(), private User(java.lang.String)]
        //2.3获取一个公共构造器 (可以传递参数，参数是构造器中的形参类)
        Constructor<User> constructor = userClass.getConstructor();
        System.out.println(constructor); //public User()
        //2.4获取一个构造器 (可以传递参数，参数是构造器中的形参类)
        Constructor<User> declaredConstructor = userClass.getDeclaredConstructor(String.class);
        System.out.println(declaredConstructor); // private User(java.lang.String)

//2.4获取一个构造器
		Constructor<User> declaredConstructor = userClass.getDeclaredConstructor(String.class);
        System.out.println(declaredConstructor); // private User(java.lang.String)
		//3.Constructor类常用方法
        //3.1获取构造器的权限修饰符
        int modifiers = declaredConstructor.getModifiers();
        System.out.println(declaredConstructor + "的构造方法的修饰符为" + modifiers);//private User(java.lang.String)的构造方法的修饰符为2(对应private)
        //3.2获取构造器的形参类型
        Class<?>[] types = declaredConstructor.getParameterTypes();
        System.out.println(declaredConstructor + "的形参类型有" + Arrays.toString(types)); //private User(java.lang.String)的形参类型有[class java.lang.String]
        //3.3通过Constructor实例化对象
        //因为获取的是私有方法，所以需要暴力反射
        declaredConstructor.setAccessible(true);//将私有构造器设置为可访问状态
        User user = declaredConstructor.newInstance( "无止境"); 
        System.out.println(user.getName()); //无止境

    //1.获取类
        Class<User> userClass = User.class;
        //2.实例私有构造器
        Constructor<User> privateConstructor = userClass.getDeclaredConstructor(String.class);
        privateConstructor.setAccessible(true);
        User user = privateConstructor.newInstance("无止境");
        //3.调用私有化方法setAge
        Method setAge = userClass.getDeclaredMethod("setAge", Integer.class);
        setAge.setAccessible(true);
        setAge.invoke(user, 18);
        System.out.println(user.getName() + "的年龄为" + user.getAge()); //无止境的年龄为18
        //4.获取私有属性 name
        Field nameField = userClass.getDeclaredField("name");
        nameField.setAccessible(true);
        String name = (String)nameField.get(user);
        System.out.println("利用反射获取的私有属性" + name); //利用反射获取的私有属性无止境

//目标接口
public interface UserService {
    void addUser(String name);
    void deleteUser(Integer id);
}
//目标实现类
public class UserServiceImpl implements UserService {
   @Override
    public void addUser(String name) {
        System.out.println("执行添加姓名为 : " + name + " 用户的操作");
    }
    @Override
    public void deleteUser(Integer id) {
        System.out.println("执行删除id为 : " + id + " 用户的操作");
    }
}

public class LogInvocationHandler implements InvocationHandler {
    private Object target; //目标对象
    public LogInvocationHandler(Object target) {
        this.target = target;
    }
    /**
     *
     * @param proxy 代理对象
     * @param method 目标方法
     * @param args 方法参数
     * @return 方法返回值
     * @throws Throwable
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //前置日志,记录日志
        System.out.println("【日志】 开始调用方法 : " + method.getName() + ",方法参数为 : " + Arrays.toString(args));
        //调用目标方法
        Object result = method.invoke(target, args);
        //后置日志，记录方法完成
        System.out.println("【日志】方法调用结束 : " + method.getName());
        return result;
    }
}

public static void main(String[] args) {
        //1.创建目标对象
        UserServiceImpl target = new UserServiceImpl();
        //2.创建InvocationHandler实例
        LogInvocationHandler handler = new LogInvocationHandler(target);
        //3.生成动态代理对象
        UserService proxy = (UserService) Proxy.newProxyInstance(
                target.getClass().getClassLoader(), //类加载器
                target.getClass().getInterfaces(), //目标实现的接口
                handler
        );
        //4.调用代理对象的方法
        proxy.addUser("无止境");
        proxy.deleteUser(1001);
    }

<dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>3.3.0</version>
        </dependency>

public class OrderService {
    //模拟创建订单方法
    public void createOrder(String orderNo) {
        System.out.println("创建订单，订单号为 : " + orderNo);
    }
}

public class TransactionMethodInterceptor implements MethodInterceptor {
    /**
     *
     * @param o 目标对象
     * @param method 目标方法
     * @param objects 方法参数
     * @param methodProxy 方法代理对象
     * @return 方法返回值
     * @throws Throwable
     */
    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        //前置增强：开启事务
        System.out.println("【事务】开启数据事务");
        //调用目标方法(通过methodProxy提高性能)
        Object result = methodProxy.invokeSuper(o, objects);
        //后置增强：提交事务
        System.out.println("【事务】提交数据事务");
        return result;
    }
}

public class CglibProxyDemo {
    public static void main(String[] args) {
        //1.创建Enhancer实例(CGLIB核心)
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(OrderService.class); //设置目标类
        enhancer.setCallback(new TransactionMethodInterceptor()); //设置增强器
        //2.生成动态代理对象
        OrderService proxy = (OrderService) enhancer.create();
        //3.调用代理对象方法
        proxy.createOrder("order_112233");
    }
}