spring创建bean的三种方式

1.空参构造方法：
空参构造方法是默认的，当在xml中配置bean的时候，当创建ioc容器的时候就会创建该bean。
(1)首先需要导入spring的三个核心依赖，core，bean，context。

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>5.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.10</version>
    </dependency>
</dependencies>

(2)xml配置文件对应的是domain中的实体类

 <bean id="people"  class="people"></bean>
@Data
public class people {
    private  String name;
    private int age;
    public  people(){
        System.out.println("我是空参构造方法");
    }

测试：

//        创建ioc容器
        ApplicationContext ap=new ClassPathXmlApplicationContext("application.xml");
        people p= ap.getBean("people",people.class);

2.1有参构造方法：constructor-arg 标签存在name index ref，通过这些设置有参构造函数的执行类型·.

import lombok.Data;

@Data
public class people {
    private  String name;
    private int age;
    public  people(){
        System.out.println("我是空参构造方法");
    }
    public  people(String name ,int age){

        System.out.println("我是有参构造方法one");
    }
    public  people(int age,String name ){

        System.out.println("我是有参构造方法tow");
    }
}
 <bean id="people2"  class="people">
        <constructor-arg index="0" value="zhang">  </constructor-arg>
        <constructor-arg index="1" value="123">  </constructor-arg>
    </bean>

2.实例工厂创建bean指的是通过工厂创建实例对象，首先需要创建工厂，在xml中也要配置工厂类。

public class peopleFactory {
    public  people  newinstence(){
        return  new people();
    }
}
 <bean id="factory" class="peopleFactory" ></bean>
    <bean id="people"  class="people" factory-bean="factory" factory-method="newinstence">
    </bean>

静态工厂，只是将工厂中的方法设置为static的，不需要创建工厂的bean

<bean id="people"   class="peopleFactory" factory-method="newinstence">
    </bean>
public class peopleFactory {
    public  static people  newinstence(){
        return  new people();
    }
}