Spring实例化bean的三种方法

1.用构造器来实例化

<bean id="hello2" class="com.hsit.hello.impl.ENhello" />

2.使用静态工厂方法实例化

要写一个bean，bean中定义一个静态方法，生成bean，配置factory-method指定静态方法，运行时容器就会自动调用静态方法生成实例

bean

package com.hsit.hello.impl;

import com.hsit.hello.IHello;

public class CHhello implements IHello {

    private String msg;

    public void sayHello() {
        System.out.println("中文" + msg);
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "Chinese";
    }

    public static CHhello createInstance() {
        System.out.println("jingtai");
        return new CHhello();
    }
}

配置文件

<bean id="hello1" class="com.hsit.hello.impl.CHhello" factory-method="createInstance" lazy-init="true">
    <!-- setter注入 -->
        <property name="msg" value="哈哈">
        </property>
    </bean>

3.使用实例工厂方法实例化

要写两个bean，一个是要实例化的bean，另一个是工厂bean。容器先实例化工厂bean，然后调用工厂bean配置项factory-method中指定的方法，在方法中实例化bean

工厂bean:

package com.hsit.hello.impl;

public class ENhelloFactory {

    public ENhello createInstance() {
        System.out.println("ENhello工厂");
        return new ENhello();
    }

    public ENhelloFactory() {
        System.out.println("chuanjian");
    }

}

要实例化的bean:

package com.hsit.hello.impl;

import com.hsit.hello.IHello;

public class ENhello implements IHello {

    @Override
    public void sayHello() {
        // TODO Auto-generated method stub
        System.out.println("hello");
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "我是ENhello";
    }
}

配置文件

<bean id="eHelloFactory" class="com.hsit.hello.impl.ENhelloFactory" />
<!-- factory-bean填上工厂bean的id，指定工厂bean的工厂方法生成实例，class属性不填 -->
<bean id="example" factory-bean="eHelloFactory" factory-method="createInstance"/>

测试代码

BeanFactory factory = new ClassPathXmlApplicationContext("applicationContext.xml");

        ENhello eNhello = (ENhello) factory.getBean("example");
        System.out.println(eNhello.toString());

         factory.getBean("hello1");