Spring 中使用反射创建 Bean 实例的几种方式

public class MyBean {
    public MyBean() {
        System.out.println("MyBean created using default constructor.");
    }
}
public class CreateBeanWithReflection {
    public static void main(String[] args) throws Exception {
        // 使用 Class.newInstance() (已过时)
        Class<MyBean> clazz = MyBean.class;
        MyBean myBean = clazz.newInstance(); // 创建 MyBean 实例
    }
}

import java.lang.reflect.Constructor;
public class MyBean {
    private String name;
    private int age;
    // 无参构造函数
    public MyBean() {
        System.out.println("MyBean created using default constructor.");
    }
    // 带参数的构造函数
    public MyBean(String name, int age) {
        System.out.println("MyBean created using parameterized constructor.");
        this.name = name;
        this.age = age;
    }
    // 私有构造函数
    private MyBean(String name){
        System.out.println("MyBean created using private constructor");
        this.name = name;
    }
}
 public class CreateBeanWithReflection {
    public static void main(String[] args) throws Exception {
         Class<MyBean> clazz = MyBean.class;
        // 1. 使用无参构造函数
        Constructor<MyBean> defaultConstructor = clazz.getDeclaredConstructor();
        MyBean myBean1 = defaultConstructor.newInstance();
        // 2. 使用带参数的构造函数
        Constructor<MyBean> parameterizedConstructor = clazz.getDeclaredConstructor(String.class, int.class);
        MyBean myBean2 = parameterizedConstructor.newInstance("John", 30);
        // 3. 使用私有构造函数
        Constructor<MyBean> privateConstructor = clazz.getDeclaredConstructor(String.class);
        privateConstructor.setAccessible(true); // 设置可访问私有构造函数
        MyBean myBean3 = privateConstructor.newInstance("Private Bean");
    }
}

import java.lang.reflect.Method;
public class MyBean {
    private String message;
    private MyBean(String message) {
        this.message = message;
    }
    // 静态工厂方法
    public static MyBean createInstance(String message) {
        return new MyBean(message);
    }
    public String getMessage(){
        return  message;
    }
}
//工厂类
public class MyBeanFactory{
     public MyBean createMyBean(String message){
         return  new MyBean(message);
     }
}
public class CreateBeanWithReflection {
    public static void main(String[] args) throws Exception {
        // 1. 使用静态工厂方法
        Class<MyBean> clazz = MyBean.class;
        Method staticFactoryMethod = clazz.getDeclaredMethod("createInstance", String.class);
        MyBean myBean1 = (MyBean) staticFactoryMethod.invoke(null, "Hello from static factory method");
         System.out.println(myBean1.getMessage());
        // 2. 使用实例工厂方法
        MyBeanFactory factory = new MyBeanFactory(); // 创建工厂实例
        Method instanceFactoryMethod = MyBeanFactory.class.getDeclaredMethod("createMyBean", String.class);
        MyBean myBean2 = (MyBean) instanceFactoryMethod.invoke(factory, "Hello from instance factory method");
        System.out.println(myBean2.getMessage());
    }
}

import org.springframework.beans.BeanUtils;
public class MyBean {
    public MyBean() {
        System.out.println("MyBean created using default constructor.");
    }
}
public class CreateBeanWithReflection {
    public static void main(String[] args) throws Exception {
        // 使用 BeanUtils.instantiateClass()
        MyBean myBean = BeanUtils.instantiateClass(MyBean.class);
    }
}