动态的创建对象（反射）及反射操作注解

注解与反射的部分实现操作

动态的创建对象（通过反射）

package reflection;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

//动态的创建对象，通过反射
public class Test03 {
    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {
        //获取Class对象
        Class c1 = Class.forName("reflection.User");

        //构造一个对象
        //User user =(User) c1.newInstance();
        //System.out.println(user);

        //通过构造器创建对象
        //Constructor constructor = c1.getDeclaredConstructor(String.class,int.class,int.class);
        //User user2 =(User) constructor.newInstance("小明", 001, 19);
        //System.out.println(user2);

        //通过反射调用普通方法
        User user3 =(User) c1.newInstance();
        //通过反射获得一个方法
        Method setName = c1.getDeclaredMethod("setName", String.class);

        //invoke : 激活的意思
        //(对象 , "方法的值")
        setName.invoke(user3,"小明");
        System.out.println(user3.getName());

        //通过反射操作属性
        User user4 =(User) c1.newInstance();
        Field name = c1.getDeclaredField("name");

        //不能直接操作私有属性，我们需要关闭程序的私有检测，属性或者方法的setAccessible(true);
        name.setAccessible(true);

        name.set(user4,"小明2");
        System.out.println(user4.getName());
    }
}

反射操作注解

package reflection;

import java.lang.annotation.*;
import java.lang.reflect.Field;

//反射操作注解
public class Test04 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("reflection.StudentNow");

        //通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        //获取注解的value的值
        TableNow tableNow =(TableNow) c1.getAnnotation(TableNow.class);
        String value = tableNow.value();
        System.out.println(value);

        //获得类指定注解(name属性)
        Field field = c1.getDeclaredField("name");
        FieldNow annotation = field.getAnnotation(FieldNow.class);
        System.out.println(annotation.columnName());
        System.out.println(annotation.type());
        System.out.println(annotation.length());
    }
}

@TableNow("db_student")
class StudentNow{
    @FieldNow(columnName = "db_id", type = "int", length = 10)
    private int id;
    @FieldNow(columnName = "db_age", type = "int", length = 10)
    private int age;
    @FieldNow(columnName = "db_name", type = "varchar", length = 3)
    private String name;

    public StudentNow() {
    }

    public StudentNow(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

//类名的注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface TableNow{
    String value();
}

//属性的注解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FieldNow{
    String columnName();
    String type();
    int length();
}