Spring實例化bean的三種方法

1.用構造器來實例化

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

2.使用靜態工廠方法實例化

要寫一個bean，bean中定義一個靜態方法，生成bean，配置factory-method指定靜態方法，運行時容器就會自動調用靜態方法生成實例

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.使用實例工廠方法實例化

要寫兩個bean，一個是要實例化的bean，另外一個是工廠bean。容器先實例化工廠bean，而後調用工廠bean配置項factory-method中指定的方法，在方法中實例化bean

工廠bean:

package com.hsit.hello.impl;

public class ENhelloFactory {

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

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

}

要實例化的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填上工廠bean的id，指定工廠bean的工廠方法生成實例，class屬性不填 -->
<bean id="example" factory-bean="eHelloFactory" factory-method="createInstance"/>

測試代碼

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

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

         factory.getBean("hello1");