bean的创建

文章目录

1. 1. 普通的bean创建
2. 2. FactoryBean创建Bean
3. 3. 其它方式创建Bean

spring在xml驱动的BeanFactory中创建bean的方式有很多种方式。

普通的bean创建

普通的bean创建方式一般是在xml文件中直接配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
	<!-- 配置一个简单的bean -->
    <bean id="mycar" class="com.study.pack.xml.factorybean.Car"></bean>
    
    <!-- 配置一个简单的bean,并为其加入name和price属性 -->
    <bean id="mycarB" class="com.study.pack.xml.factorybean.Car">
        <property name="name" value="宝马"/>
        <property name="price" value="2000"/>
    </bean>
</beans>

public class Test {
    public static void main(String[] args) {
        XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("factory-bean.xml"));
        Car carA = (Car)factory.getBean("mycarA");
        Car carB = (Car)factory.getBean("mycarB");
        System.out.println(carA);
        System.out.println(carB);
    }
    // 输出结果
    // null--0.0
	// 宝马--2000.0
}   

@Data
public class Car {
    private String name;
    private double price;

    @Override
    public String toString() {
        return this.name + "--" + this.price;
    }
}

FactoryBean创建Bean

FactoryBean创建bean的不同之处在于增加了一个FactoryBean实现类，该类负责相关bean的创建细节，而在xml中配置的也是该FactoryBean的信息。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
	<!-- 通过指定的FactoryBean创建Bean -->
    <bean id="car" class="com.study.pack.xml.factorybean.CarFactoryBean">
        <property name="message" value="比亚迪,20000"/>
    </bean>
</beans>

public class FactoryBeanTest {

    public static void main(String[] args) {
        XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("factory-bean.xml"));
        Car car = (Car) factory.getBean("car");
        // 加上&是只返回该FactoryBean实例
        CarFactoryBean carFactoryBean = (CarFactoryBean) factory.getBean("&car");
        System.out.println(car);
        System.out.println(carFactoryBean);
    }
    // 输出信息
    // 比亚迪--20000.0
    // 比亚迪,20000
}

public class CarFactoryBean implements FactoryBean<Car> {
	private String message;

    @Override
    public Car getObject() throws Exception {
        Car car = new Car();
        String[] messageArray = message.split(",");
        car.setName(messageArray[0]);
        car.setPrice(Double.parseDouble(messageArray[1]));
        return car;
    }

    @Override
    public Class<?> getObjectType() {
        return Car.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    @Override
    public String toString() {
        return this.message;
    }
}

其它方式创建Bean

除了以上两种创建方式之外，spring还可以通过工厂方法来创建实例，工厂方法创建bean实例分两种情况，一种是通过静态方法创建，另一种是通过非静态方法创建。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    
    <!-- 静态方法 -->
    <bean id="secondCar" class="com.study.pack.xml.factorybean.SimpleCarFactory" factory-method="getCar"/>
    
    <!-- 非静态方法 -->
    <bean id="firstCar" factory-bean="simpleCarFactory" factory-method="createCar"/>
    <bean id="simpleCarFactory" class="com.study.pack.xml.factorybean.SimpleCarFactory"/>
    
</beans>

public class Test {
    public static void main(String[] args) {
        XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("factory-bean.xml"));
        Car firstCar = (Car)factory.getBean("firstCar");
        Car secondCar = (Car)factory.getBean("secondCar");
        System.out.println(firstCar);
        System.out.println(secondCar);
    }
    // 输出
    //吉利--200.0
	//保时捷--150000.0
}

public class SimpleCarFactory {

    // 静态方法
    public static Car getCar() {
        Car car = new Car();
        car.setName("保时捷");
        car.setPrice(150000);
        return car;
    }

    // 非静态方法
    public Car createCar() {
        Car car = new Car();
        car.setName("吉利");
        car.setPrice(200);
        return car;
    }
}