java增强：反射机制，内省机制

旧城等待， 2022-05-12 06:34 266阅读 0赞

1.  反射机制概念
2.  发射的使用场景
3.  内省机制的使用

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### part1 ：反射机制(  jdk提供的一套api,  用于动态创建对象 ) ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2V5ZW9mZWFnbGU_size_16_color_FFFFFF_t_70][]

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### ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2V5ZW9mZWFnbGU_size_16_color_FFFFFF_t_70 1][] ###

### part2:  反射的使用----两个对象间属性值的复制 ###

（浅copy:  复制一个对象，会调用构造函数)

一个存在继承关系的类：  对象的浅copy 代码实现如下

1, 定义两个javabean

public class Per {
        //属性
        private int age;
        private String name;
    
        //构造
        public Per(int age, String name) {
            this.age = age;
            this.name = name;
        }
        public Per() {
            System.out.println("per 无参构造");
        }
    
        //get,set
        public int getAge() {       return age;  }
        public void setAge(int age) {      this.age = age;  }
        public String getName() {     return name; }
        public void setName(String name) {     this.name = name; }
    }
    
    public class Student extends Per{
        private int score;
        public int getScore(){return score;}
        public void setScore(int score){this.score=score;}
    }

2, 创建对象1， 复制为对象2-----------反射：(构造+ 字段   ),  ( 构造 + set/get  )，（构造+ get)

//创建对象： 有属性
    Student st = new Student();
    @before
    public void init(){     
         st.setName("yyyy");
         st.setAge(23);
         st.setScore(99)
    }
    
     /**
         * 反射： 通过属性---copy对象
         * @throws Exception
         */
        @Test
        public void t1() throws Exception {       
            //创建对象： 带参构造
            Class<?> clazz = Class.forName("Student");
            Constructor<?> cons = clazz.getDeclaredConstructor(int.class);
            Student student = (Student) cons.newInstance(80);
            //获取: 父类属性--------------------------
            Class<?> sup = clazz.getSuperclass();
            Field age = sup.getDeclaredField("age");
            age.setAccessible(true);
            Field name = sup.getDeclaredField("name");
            name.setAccessible(true);
            //赋值
            age.set(student,st.getAge());
            name.set(student,st.getName());
            System.out.println(student.getName() + "," + student.getAge()+","+student.getScore());
        }
    
     /**
         * 反射： 通过方法----copy对象
         * @throws Exception
         */
        @Test
        public void t2() throws Exception {     
            //创建对象： 带参构造
            Class<?> clazz = Class.forName("Student");
            Constructor<?> cons = clazz.getDeclaredConstructor(int.class);
            Student student = (Student) cons.newInstance(89);
            //获取: 父类方法
            Method setAge = clazz.getMethod("setAge", int.class);
            Method setName = clazz.getMethod("setName", String.class);
            //赋值
            setAge.invoke(student, st.getAge());
            setName.invoke(student, st.getName());
            System.out.println(student.getName() + "," + student.getAge()+","+student.getScore());
        }
    
    @Test
        public void t3() throws Exception {
            /**
             * get--->set方法名,  参数
             */
             //创建对象       
            Class<?> clazz = Class.forName("Student");
            Student st2 = (Student) = clazz.newInstance();
            //get方法---》set赋值
            Class clazz = st.getClass();
            Method[] ms = clazz.getMethods();
    
            //判断： 是否getAge()
            for (Method m : ms) {
                String get = m.getName();
                Class<?>[] paramType = m.getParameterTypes();
                Class<?> retType = m.getReturnType();
    
                if (get.startsWith("get") && paramType.length == 0 && retType != Class.class) {
                    Object returnVal = m.invoke(st);
                    String set = get.replace("get", "set");
                    //set : 参数---->第二个Obj赋值
                    Method setMetho = clazz.getMethod(set, retType);
                    setMetho.invoke(st2, returnVal);
                }
            }
            System.out.println(st2.getName() + "," + st2.getAge() );
        }

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### part3:  内省机制---对象copy ###

@Test
        public void t4() throws Exception {
    
            Student st = new Student();
            st.setAge(40);
            st.setName("aaaa");
            st.setScore(99);
            Student st2 = new Student();
    
            /**
             * 内省： 实现---2个对象：  属性拷贝
             */
            BeanInfo binfo = Introspector.getBeanInfo(st.getClass());
            PropertyDescriptor[] propDes = binfo.getPropertyDescriptors();
    
            for (PropertyDescriptor proDescriptor : propDes) {
    
                Method read = proDescriptor.getReadMethod();
                Method write = proDescriptor.getWriteMethod();
                String fieldName = proDescriptor.getName();
    
                if (read != null && write != null) {
                    if (!fieldName.equals("class"))
                        write.invoke(st2, read.invoke(st));
                }
            }
            System.out.println(st2.getName() + "," + st2.getAge()+ ","+st2.getScore());
        }

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### part4: 对象的深度copy   ###

( 不会调用构造方法，  父类和子类： 都要 implements Serializable)

@Test
        public void t5() throws IOException, ClassNotFoundException {
            Student st = new Student();
            st.setAge(40);
            st.setName("aaaa");
    
            //把各个属性：  组合为byte[]
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream objout = new ObjectOutputStream(baos);
            objout.writeObject(st);
            baos.close();
            objout.close();
    
            ObjectInputStream objin = new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray()));
            Student student= (Student) objin.readObject();
            objin.close();
            System.out.println(student.getName() + "," + student.getAge()+","+student.getScore());
        }

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