2021-12-19 实例化bean的方式

一、实例化bean的方式

1、通过构造方法的方式
2、通过静态方法的方式
3、通过实例化工厂的方式

下面通过代码过一个demo

• 通过构造方法的方式
  1)首先创建一个SpringBean 并提供一个构造方法如下所示

public class SpringBean {
    String name;
    int age;

    public SpringBean(){
        System.out.println("springbean create,by not params construct function");
    }

    public SpringBean(String name,int age){
        this.name=name;
        this.age=age;
        System.out.println("springbean create，by construct function");
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

2）applicationContext.xml 的创建方式如下所示

//一种是无参构造方法的方式
<bean id="springBean1" class="springioc6.SpringBean">
        <property name="name" value="mumu"></property>
        <property name="age" value="18"></property>
    </bean>
//另一种是通过有参构造方法的方式
<bean id="springBean2" class="springioc6.SpringBean">
     <constructor-arg name="name" value="mumu"></constructor-arg>
     <constructor-arg name="age" value="28"></constructor-arg>
 </bean>

• 通过静态方法的方式,此处的构建方式类似工厂模式，通过一个工厂的静态方法创建出一个对象。

public class SpringBeanFactory {

    /**
     * 不带参数的
     * @return
     */
    public static SpringBean getInstanceSpringBean(){
        SpringBean sbean=new SpringBean();
        return sbean;
    }

    /**
     * 带参数的
     * @return
     */
    public static SpringBean getInstanceSpringBeanWithParam(String name,int age){
        SpringBean sbean=new SpringBean();
        sbean.setName(name);
        sbean.setAge(age);
        return sbean;
    }
}

applicationContext.xml 的配置方法如下

 <bean id="springbeanfactory" class="springioc7.SpringBeanFactory" factory-method="getInstanceSpringBean">
        <property name="name" value="mouse"></property>
        <property name="age" value="23"></property>
    </bean>

    <bean id="springbeanfactoryParam" class="springioc7.SpringBeanFactory" factory-method="getInstanceSpringBeanWithParam">
        <constructor-arg name="name" value="line"></constructor-arg>
        <constructor-arg name="age" value="13"></constructor-arg>
    </bean>

• 通过实例化工厂的方式

public class SpringBeanFactory {

    /**
     * 不带参数的
     * @return
     */
    public  SpringBean getInstanceSpringBean(){
        SpringBean sbean=new SpringBean();
        return sbean;
    }

    /**
     * 带参数的
     * @return
     */
    public  SpringBean getInstanceSpringBeanWithParam(String name, int age){
        SpringBean sbean=new SpringBean(name,age);
        return sbean;
    }
}

applicationContext.xml 的配置如下 首先要有一个工厂bean 然后再通过这个工厂bean 中的方法获得想要创建的对象。 主要涉及的属性是 factory-bean和factory-method

 <bean id="factorySpring" class="springioc8.SpringBeanFactory"></bean>

    <bean id="springbeanfactory" factory-bean="factorySpring" factory-method="getInstanceSpringBean">
        <property name="name" value="glacss"></property>
        <property name="age" value="23"></property>
    </bean>

    <bean id="springbeanfactoryParam" factory-bean="factorySpring" factory-method="getInstanceSpringBeanWithParam">
        <constructor-arg name="name" value="flower"></constructor-arg>
        <constructor-arg name="age" value="10"></constructor-arg>
    </bean>