反射

反射机制是在运行状态中
对于任意一个类、都能够知道这个类所有的属性和方法
对于任意一个对象、都能够调用他的任意一个属性和方法

反射提供的功能

运行时判断任意一个对象所属的类
运行时构造任意一个类的对象
运行时判断任意一个类所具有的成员变量和方法
运行时调用一个对象的方法
生成动态代理

反射入口

获取Class的三种方法

• Class.forName() （使用较多）

Class<?> clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    System.out.println(clazz);
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

• 类名.class

System.out.println(MyInterfaceImpl.class);

• 对象.getClass

MyInterfaceImpl myInterface = new MyInterfaceImpl();
Class<? extends MyInterfaceImpl> aClass = myInterface.getClass();
System.out.println(aClass);

获取方法

Class<?> clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    //获取所有的公共方法（本类以及父类、接口中的所有方法  符合的访问修饰符规律的方法）
    Method[] methods = clazz.getMethods();
    for(Method method: methods){
        System.out.println(method);
    }
    System.out.println("-------------");
    //当前类的所有方法、不收访问修饰符的限制
    Method[] declaredMethods = clazz.getDeclaredMethods();
    for (Method declare:declaredMethods){
        System.out.println(declare);
    }
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

公共方法：本类以及父类、接口中的所有方法
符合的访问修饰符规律的方法

获取接口

Class clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    Class[] interfaces = clazz.getInterfaces();
    for (Class inter: interfaces){
        System.out.println(inter);
    }
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

获取父类

Class clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    Class superclass = clazz.getSuperclass();
    System.out.println(superclass);
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

获取构造方法

Class clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    Constructor[] constructors = clazz.getConstructors();
    for(Constructor constructor: constructors){
        System.out.println(constructor);
    }
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

获取属性

Class clazz = null;
try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    //获取共有的属性
    Field[] fields = clazz.getFields();
    for (Field field : fields){
        System.out.println(field);
    }
    //获取本类的属性
    Field[] declaredFields = clazz.getDeclaredFields();
    for (Field fie : declaredFields){
        System.out.println(fie);
    }
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

获取类的类的对象

Class clazz = null;
        try {
            clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
            //获取当前反射所代表类（接口）的实例对象
            MyInterfaceImpl o = (MyInterfaceImpl)clazz.newInstance();
            o.getInterface1();
            o.getInterface2();

        }catch (ClassNotFoundException e){
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }

操作属性和方法

Class clazz = null;

try {
    clazz = Class.forName("com.dream.xiaobo.reflect.impl.MyInterfaceImpl");
    //获取到反射类的对象
    MyInterfaceImpl instance = (MyInterfaceImpl) clazz.newInstance();
    //获取到id属性
    Field id = clazz.getDeclaredField("id");

    //屏蔽private修饰符
    id.setAccessible(true);
    //给id赋值
    id.set(instance,1);
    System.out.println(instance.getId());

    System.out.println("---------------");
    //获取到student方法
    Method method = clazz.getDeclaredMethod("student", String.class);

    //屏蔽private修饰符
    method.setAccessible(true);

    //调用方法
    method.invoke(instance,"xiaobo");

    System.out.println("---------------");


    //获取public修饰符的构造方法
    Constructor constructor1 = clazz.getDeclaredConstructor(String.class);
    //调用构造方法
    MyInterfaceImpl xiaobo = (MyInterfaceImpl)constructor1.newInstance("xiaobo");

    System.out.println("---------------");
    
    //获取private修饰符的构造方法
    Constructor constructor2 = clazz.getDeclaredConstructor(Integer.class);
    //屏蔽private修饰符访问权限
    constructor2.setAccessible(true);
    //调用构造方法
    MyInterfaceImpl wyb = (MyInterfaceImpl)constructor2.newInstance(1);

}catch (ClassNotFoundException e){
    e.printStackTrace();
} catch (NoSuchFieldException e) {
    e.printStackTrace();
} catch (IllegalAccessException e) {
    e.printStackTrace();
} catch (InstantiationException e) {
    e.printStackTrace();
} catch (NoSuchMethodException e) {
    e.printStackTrace();
} catch (InvocationTargetException e) {
    e.printStackTrace();
}

越过泛型检查

List<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);

Class clazz = list.getClass();
try {
    Method method = clazz.getMethod("add",Object.class);

    method.invoke(list,"xiaobo");

    System.out.println(list);

简单应用

public static void propertyUtils(Object type,String name,Object value){

        Class<?> clazz = type.getClass();

        try {
            Field field = clazz.getDeclaredField(name);

            field.setAccessible(true);
            field.set(type,value);

        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }

MyInterfaceImpl myInterface = new MyInterfaceImpl();

            PropertyUtils.propertyUtils(myInterface,"id",1);
            PropertyUtils.propertyUtils(myInterface,"name","xiaobo");
            System.out.println(myInterface.getId());
            System.out.println(myInterface.getName());

            Student student = new Student();
            PropertyUtils.propertyUtils(student,"score",99.99);
            System.out.println(student.getScore());

正确的开始、微小的长进、然后持续、嘿、我是小博、带你一起看我目之所及的世界……