Spring笔记之Bean实例的创建方式以及依赖配置

Bean实例的创建通常有如下3中方式：

1、通过构造方法创建Bean

package com.test;
public class Person {
	public Person() {
		System.out.println("Person 构造方法");
	}

	private Hobby hobby;

	public void setHobby(Hobby hobby) {
		System.out.println("通过依赖关系注入");
		this.hobby = hobby;
	}

	public void singASong() {
		System.out.println(hobby.doIt());
	}
}

interface Hobby {
	public String doIt();
}

class Sing implements Hobby {
	public Sing() {
		System.out.println("Sing 构造方法");
	}

	public String doIt() {
		return "I am singing.";
	}
}

 

package com.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTest {
	public static void main(String[] args) {
		ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
		Person p = ctx.getBean("person", Person.class);
		p.singASong();
	}
}

 

<?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"
	xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
				http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd
				http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">

<bean id="person" class="com.test.Person">
	<property name="hobby" ref="hobbySing"></property>
</bean>

<bean id="hobbySing" class="com.test.Sing"></bean>
	
</beans>

 2、使用静态工厂方法创建Bean

 

package com.test2;

public class PersonCreator {
	public static People createPerson(String type) {
		if (type.equals("chn")) {
			return new Chinese();
		}
		if (type.equals("jpn")) {
			return new Japanese();
		}

		return null;
	}
}

 

package com.test2;

public interface People {
	public void say();
}

class Chinese implements People {

	public void say() {
		System.out.println("I am Chinese.");
	}

}

class Japanese implements People {

	public void say() {
		System.out.println("I am Japanese.");
	}

}

 工厂方法一定要static

<?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"
	xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
				http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd
				http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">

	<!-- 静态工厂方法 -->
	<bean id="chinese" class="com.test2.PersonCreator" factory-method="createPerson">
		<constructor-arg value="chn" />
	</bean>
	<bean id="japanese" class="com.test2.PersonCreator" factory-method="createPerson">
		<constructor-arg value="jpn" />
	</bean>

</beans>

 

package com.test2;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
	public static void main(String[] args) {
		
		ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
		People chn = ctx.getBean("chinese", People.class);
		chn.say();
		People jpn = ctx.getBean("japanese", People.class);
		jpn.say();
		
	}
}

 输出：I am Chinese.

I am Japanese.

3、调用实例工厂方法创建Bean

注：实例工厂方法与静态工厂方法只有一点不同

静态工厂方法：只需使用工厂类即可，工厂方法必须static

实例工厂方法：必须使用工厂类的实例，工厂方法必须non-static

package com.test2;

public class PersonCreator {
	public People createPerson(String type) {
		if (type.equals("chn")) {
			return new Chinese();
		}
		if (type.equals("jpn")) {
			return new Japanese();
		}

		return null;
	}
}

 

package com.test2;

public interface People {
	public void say();
}

class Chinese implements People {

	public void say() {
		System.out.println("I am Chinese.");
	}

}

class Japanese implements People {

	public void say() {
		System.out.println("I am Japanese.");
	}

}

 

package com.test2;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
	public static void main(String[] args) {
		
		ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
		People chn = ctx.getBean("chinese", People.class);
		chn.say();
		People jpn = ctx.getBean("japanese", People.class);
		jpn.say();
		
	}
}

 

<?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"
	xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
				http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd
				http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
	
	<!-- 实例工厂方法 -->
	<bean id="creator" class="com.test2.PersonCreator"/>
	
	<bean id="chinese" factory-bean="creator" factory-method="createPerson">
		<constructor-arg value="chn" />
	</bean>
	
	<bean id="japanese" factory-bean="creator" factory-method="createPerson">
		<constructor-arg value="jpn" />
	</bean>

</beans>

 输出：

I am Chinese.

I am Japanese.

 

总结：大多数情况下，BeanFactory直接通过new关键字调用构造器来创建Bean实例，而class属性指定了Bean实例的实现类。因此，<bean .../>元素必须指定Bean实例的class属性，但这并不是唯一的实例化Bean的方法。

使用实例工厂方法创建Bean实例，以及使用子Bean方法创建Bean实例时，都可以不指定class属性。