Java - 注解应用 August 21，2019

package testannotation;

import  java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.FIELD,ElementType.CONSTRUCTOR,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)//运行时
public @interface MyAnnotation {
     String [] value();
}

package testannotation;

public class Person {
        private String name;
        private Integer age;
        private String sex;
        @MyAnnotation({"杨晓航","20","男"})
        public Person(){}

        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public Integer getAge() {
            return age;
        }
        public void setAge(Integer age) {
            this.age = age;
        }
        public String getSex() {
            return sex;
        }
        public void setSex(String sex) {
            this.sex = sex;
        }

}

public class User {
    private String username;
    private String password;
    private Float balance;

    @MyAnnotation({"杨晓航","123","10000"})
    public User(){}

    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Float getBalance() {
        return balance;
    }
    public void setBalance(Float balance) {
        this.balance = balance;
    }

}

package testannotation;
import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class MySpring {

    public Object getBean(String classname){
        Object obj = null;
        try {
            //1.先通过传递的类名获得对应的Class
            Class clazz = Class.forName(classname);
            //2.通过Class获取无参数的构造方法
            Constructor con = clazz.getConstructor();
            //3.构造方法创建一个对象
            obj = con.newInstance();

            //4.获取属性的值
            Annotation a = con.getAnnotation(MyAnnotation.class);
            //5.执行value方法
            Class clazz2 = a.getClass();
            Method method = clazz2.getMethod("value");
            String [] values = (String[]) method.invoke(a);
            //6.将values的值存入属性中
            //找寻属性对应的set方法赋值
            //获取传递的Class类全部的私有属性
            Field[] filelds = clazz.getDeclaredFields();
            for(int i = 0; i < filelds.length; i++){
                //获取属性的名字
                String fieldName = filelds[i].getName();
                String firstName = fieldName.toUpperCase().substring(0,1);
                String nextName = fieldName.substring(1);
                StringBuilder stringBuilder = new StringBuilder("set");
                stringBuilder.append(firstName);
                stringBuilder.append(nextName);
                //将值通过调用对应的set方法存入属性
                        //获取数据类型
                Class fieldType = filelds[i].getType();
                //方法名字，数据类型
                Method setMethod = clazz.getMethod(stringBuilder.toString(),fieldType);
                //需要将注解内读取到的String类型的值 转化成属性类型对应的值
                setMethod.invoke(obj,fieldType.getConstructor(String.class).newInstance(values[i]));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return obj;
    }
}

package testannotation;

public class TestMain {
    public static void main(String []args){
        MySpring ms = new MySpring();
        Person person = (Person) ms.getBean("testannotation.Person");
        System.out.println(person.getName()+"--"+person.getSex()+"--"+person.getAge());
        User user = (User) ms.getBean("testannotation.User");
        System.out.println(user.getBalance()+"--"+user.getPassword()+"--"+user.getUsername());
    }
}