ioc创建对象

ioc创建对象

1.含有参构造时

User.java

public class User {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public void show(){
        System.out.println("name:"+name);
    }
}

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="user" class="com.liu.pojo.User">
        <property name="name" value="张三" />
    </bean>

</beans>

测试

public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
    User user = (User) context.getBean("user");
    user.show();
}

当有参构造存在时可直接通过class获取

2.不存在无参构造时

1.使用下标赋值

User.java为

public class User {
    private String name;

    public User(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public void show(){
        System.out.println("name:"+name);
    }
}

此时需要用constructor-arg

<bean id="user" class="com.liu.pojo.User">
    <constructor-arg index="0" value="张三" />
</bean>

2.通过类型创建，如有多个相同类型无法使用，不推荐

<bean id="user" class="com.liu.pojo.User">
    <constructor-arg type="java.lang.String" value="张三"/>
</bean>

3.直接通过参数名创建

<bean id="user" class="com.liu.pojo.User">
    <constructor-arg name="name" value="张三"/>
</bean>

总结：

在配置文件加载的时候，容器中管理的对象已经初始化了，切无论调用生成几个对象且都是同一个