Spring中Bean实例化的几种方式

Bean实例化的几种方式

1. 类构造方法实例化
2. 工厂类静态方法实例化
3. 工厂类普通方法实例化

新建包BeanInstance

新建普通类UserService.java

package BeanInstance;

import java.text.MessageFormat;

public class UserService {

    public UserService(String username){
        System.out.println(MessageFormat.format("我是{0}！",username));
    }

    public void greeting(String nickname) {
        System.out.println(MessageFormat.format("你好，{0}！", nickname));
    }
}

新建单元测试类BeanTest.java

import org.junit.Test;

public class BeanTest {
}

类构造方法实例化

• 不通过配置文件配置Bean

进行单元测试BeanTest.java

    @Test
    public void classTest() {
        /**
         * 测试类直接实例化
         */

        UserService userService = new UserService("猫头鹰");

        userService.greeting("黑虎");
    }

• 通过配置文件beanInstance.xml

beanInstance.xml配置

    <bean id="userServiceByConstruct" class="BeanInstance.UserService">
        <constructor-arg name="username" value="夜莺"/>
    </bean>

进行单元测试BeanTest.java

    @Test
    public void beanConstructTest() {
        /**
         * 测试类构造方法进行Bean实例化
         */

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beanInstance.xml");

        UserService userService = (UserService) applicationContext.getBean("userServiceByConstruct");

        userService.greeting("黑虎");
    }

工厂类静态方法实例化Bean

• 不通过配置文件配置Bean

新建工厂类StaticBeanFactory.java，并添加静态方法

package BeanInstance;

public class StaticBeanFactory {
    public static UserService getUserService() {
        return new UserService("土狼");
    }
}

进行单元测试BeanTest.java

    @Test
    public void staticTest(){
        /**
         * 测试静态方法实例化
         */
        UserService userService=StaticBeanFactory.getUserService();

        userService.greeting("猎豹");
    }

• 通过配置文件beanInstance.xml

beanInstance.xml配置

    <bean id="userServiceByStatic" class="BeanInstance.StaticBeanFactory" factory-method="getUserService"/>

进行单元测试BeanTest.java

    @Test
    public void beanStaticTest() {
        /**
         * 测试静态方法进行Bean实例化
         */

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beanInstance.xml");

        UserService userService = (UserService) applicationContext.getBean("userServiceByStatic");

        userService.greeting("猎豹");
    }

工厂类普通方法实例化Bean

• 不通过配置文件配置Bean

新建工厂类InstanceBeanFactory.java，并添加静态方法

package BeanInstance;

public class InstanceBeanFactory {
    public UserService getUserService() {
        return new UserService("二狗子");
    }
}

• 通过配置文件beanInstance.xml

beanInstance.xml配置

    <bean id="instanceBeanFactory" class="BeanInstance.InstanceBeanFactory"/>
    <bean id="userServiceByInstance" class="BeanInstance.UserService" factory-bean="instanceBeanFactory"
          factory-method="getUserService"/>

进行单元测试BeanTest.java

    @Test
    public void beanInstanceTest() {
        /**
         * 测试实例方法进行Bean实例化
         */

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beanInstance.xml");

        UserService userService = (UserService) applicationContext.getBean("userServiceByInstance");

        userService.greeting("大英子");
    }

配置总结

beanInstance.xml关键点

类构造方法实例化Bean

有参构造使用标签进行参数注入：constructor-arg

工厂类静态方法实例化Bean

只需声明工厂类，但需指定factory-method为获取类实例的方法

工厂类普通方法实例化Bean

需声明类及其工厂类，类Bean指定factory-bean为其工厂类，指定factory-method为其获取实例的方法

源码下载

[email protected]:Angryshark128/Practice.git